Imported from /home/lorry/working-area/delta_berkeleydb/db-6.1.23.tar.gz.HEADdb-6.1.23master

1 files changed, 3412 insertions, 1335 deletions

diff --git a/lang/sql/sqlite/ext/fts3/fts3.c b/lang/sql/sqlite/ext/fts3/fts3.c
index 20da0516..44b7f431 100644
--- a/lang/sql/sqlite/ext/fts3/fts3.c
+++ b/lang/sql/sqlite/ext/fts3/fts3.c
@@ -70,7 +70,7 @@
 ** A doclist is stored like this:
 **
 ** array {
-**   varint docid;
+**   varint docid;          (delta from previous doclist)
 **   array {                (position list for column 0)
 **     varint position;     (2 more than the delta from previous position)
 **   }
@@ -101,8 +101,8 @@
 ** at D signals the start of a new column; the 1 at E indicates that the
 ** new column is column number 1.  There are two positions at 12 and 45
 ** (14-2 and 35-2+12).  The 0 at H indicate the end-of-document.  The
-** 234 at I is the next docid.  It has one position 72 (72-2) and then
-** terminates with the 0 at K.
+** 234 at I is the delta to next docid (357).  It has one position 70
+** (72-2) and then terminates with the 0 at K.
 **
 ** A "position-list" is the list of positions for multiple columns for
 ** a single docid.  A "column-list" is the set of positions for a single
@@ -286,20 +286,15 @@
 ** will eventually overtake the earlier data and knock it out.  The
 ** query logic likewise merges doclists so that newer data knocks out
 ** older data.
-**
-** TODO(shess) Provide a VACUUM type operation to clear out all
-** deletions and duplications.  This would basically be a forced merge
-** into a single segment.
 */
 
+#include "fts3Int.h"
 #if !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_FTS3)
 
 #if defined(SQLITE_ENABLE_FTS3) && !defined(SQLITE_CORE)
 # define SQLITE_CORE 1
 #endif
 
-#include "fts3Int.h"
-
 #include <assert.h>
 #include <stdlib.h>
 #include <stddef.h>
@@ -313,6 +308,11 @@
   SQLITE_EXTENSION_INIT1
 #endif
 
+static int fts3EvalNext(Fts3Cursor *pCsr);
+static int fts3EvalStart(Fts3Cursor *pCsr);
+static int fts3TermSegReaderCursor(
+    Fts3Cursor *, const char *, int, int, Fts3MultiSegReader **);
+
 /* 
 ** Write a 64-bit variable-length integer to memory starting at p[0].
 ** The length of data written will be between 1 and FTS3_VARINT_MAX bytes.
@@ -330,21 +330,37 @@ int sqlite3Fts3PutVarint(char *p, sqlite_int64 v){
   return (int) (q - (unsigned char *)p);
 }
 
+#define GETVARINT_STEP(v, ptr, shift, mask1, mask2, var, ret) \
+  v = (v & mask1) | ( (*ptr++) << shift );                    \
+  if( (v & mask2)==0 ){ var = v; return ret; }
+#define GETVARINT_INIT(v, ptr, shift, mask1, mask2, var, ret) \
+  v = (*ptr++);                                               \
+  if( (v & mask2)==0 ){ var = v; return ret; }
+
 /* 
 ** Read a 64-bit variable-length integer from memory starting at p[0].
 ** Return the number of bytes read, or 0 on error.
 ** The value is stored in *v.
 */
 int sqlite3Fts3GetVarint(const char *p, sqlite_int64 *v){
-  const unsigned char *q = (const unsigned char *) p;
-  sqlite_uint64 x = 0, y = 1;
-  while( (*q&0x80)==0x80 && q-(unsigned char *)p<FTS3_VARINT_MAX ){
-    x += y * (*q++ & 0x7f);
-    y <<= 7;
-  }
-  x += y * (*q++);
-  *v = (sqlite_int64) x;
-  return (int) (q - (unsigned char *)p);
+  const char *pStart = p;
+  u32 a;
+  u64 b;
+  int shift;
+
+  GETVARINT_INIT(a, p, 0,  0x00,     0x80, *v, 1);
+  GETVARINT_STEP(a, p, 7,  0x7F,     0x4000, *v, 2);
+  GETVARINT_STEP(a, p, 14, 0x3FFF,   0x200000, *v, 3);
+  GETVARINT_STEP(a, p, 21, 0x1FFFFF, 0x10000000, *v, 4);
+  b = (a & 0x0FFFFFFF );
+
+  for(shift=28; shift<=63; shift+=7){
+    u64 c = *p++;
+    b += (c&0x7F) << shift;
+    if( (c & 0x80)==0 ) break;
+  }
+  *v = b;
+  return (int)(p - pStart);
 }
 
 /*
@@ -352,10 +368,21 @@ int sqlite3Fts3GetVarint(const char *p, sqlite_int64 *v){
 ** 32-bit integer before it is returned.
 */
 int sqlite3Fts3GetVarint32(const char *p, int *pi){
- sqlite_int64 i;
- int ret = sqlite3Fts3GetVarint(p, &i);
- *pi = (int) i;
- return ret;
+  u32 a;
+
+#ifndef fts3GetVarint32
+  GETVARINT_INIT(a, p, 0,  0x00,     0x80, *pi, 1);
+#else
+  a = (*p++);
+  assert( a & 0x80 );
+#endif
+
+  GETVARINT_STEP(a, p, 7,  0x7F,     0x4000, *pi, 2);
+  GETVARINT_STEP(a, p, 14, 0x3FFF,   0x200000, *pi, 3);
+  GETVARINT_STEP(a, p, 21, 0x1FFFFF, 0x10000000, *pi, 4);
+  a = (a & 0x0FFFFFFF );
+  *pi = (int)(a | ((u32)(*p & 0x0F) << 28));
+  return 5;
 }
 
 /*
@@ -420,17 +447,31 @@ static void fts3GetDeltaVarint(char **pp, sqlite3_int64 *pVal){
 }
 
 /*
-** As long as *pp has not reached its end (pEnd), then do the same
-** as fts3GetDeltaVarint(): read a single varint and add it to *pVal.
-** But if we have reached the end of the varint, just set *pp=0 and
-** leave *pVal unchanged.
+** When this function is called, *pp points to the first byte following a
+** varint that is part of a doclist (or position-list, or any other list
+** of varints). This function moves *pp to point to the start of that varint,
+** and sets *pVal by the varint value.
+**
+** Argument pStart points to the first byte of the doclist that the
+** varint is part of.
 */
-static void fts3GetDeltaVarint2(char **pp, char *pEnd, sqlite3_int64 *pVal){
-  if( *pp>=pEnd ){
-    *pp = 0;
-  }else{
-    fts3GetDeltaVarint(pp, pVal);
-  }
+static void fts3GetReverseVarint(
+  char **pp, 
+  char *pStart, 
+  sqlite3_int64 *pVal
+){
+  sqlite3_int64 iVal;
+  char *p;
+
+  /* Pointer p now points at the first byte past the varint we are 
+  ** interested in. So, unless the doclist is corrupt, the 0x80 bit is
+  ** clear on character p[-1]. */
+  for(p = (*pp)-2; p>=pStart && *p&0x80; p--);
+  p++;
+  *pp = p;
+
+  sqlite3Fts3GetVarint(p, &iVal);
+  *pVal = iVal;
 }
 
 /*
@@ -450,6 +491,8 @@ static int fts3DisconnectMethod(sqlite3_vtab *pVtab){
   sqlite3_free(p->zSegmentsTbl);
   sqlite3_free(p->zReadExprlist);
   sqlite3_free(p->zWriteExprlist);
+  sqlite3_free(p->zContentTbl);
+  sqlite3_free(p->zLanguageid);
 
   /* Invoke the tokenizer destructor to free the tokenizer. */
   p->pTokenizer->pModule->xDestroy(p->pTokenizer);
@@ -489,16 +532,19 @@ static void fts3DbExec(
 ** The xDestroy() virtual table method.
 */
 static int fts3DestroyMethod(sqlite3_vtab *pVtab){
-  int rc = SQLITE_OK;              /* Return code */
   Fts3Table *p = (Fts3Table *)pVtab;
-  sqlite3 *db = p->db;
+  int rc = SQLITE_OK;              /* Return code */
+  const char *zDb = p->zDb;        /* Name of database (e.g. "main", "temp") */
+  sqlite3 *db = p->db;             /* Database handle */
 
   /* Drop the shadow tables */
-  fts3DbExec(&rc, db, "DROP TABLE IF EXISTS %Q.'%q_content'", p->zDb, p->zName);
-  fts3DbExec(&rc, db, "DROP TABLE IF EXISTS %Q.'%q_segments'", p->zDb,p->zName);
-  fts3DbExec(&rc, db, "DROP TABLE IF EXISTS %Q.'%q_segdir'", p->zDb, p->zName);
-  fts3DbExec(&rc, db, "DROP TABLE IF EXISTS %Q.'%q_docsize'", p->zDb, p->zName);
-  fts3DbExec(&rc, db, "DROP TABLE IF EXISTS %Q.'%q_stat'", p->zDb, p->zName);
+  if( p->zContentTbl==0 ){
+    fts3DbExec(&rc, db, "DROP TABLE IF EXISTS %Q.'%q_content'", zDb, p->zName);
+  }
+  fts3DbExec(&rc, db, "DROP TABLE IF EXISTS %Q.'%q_segments'", zDb,p->zName);
+  fts3DbExec(&rc, db, "DROP TABLE IF EXISTS %Q.'%q_segdir'", zDb, p->zName);
+  fts3DbExec(&rc, db, "DROP TABLE IF EXISTS %Q.'%q_docsize'", zDb, p->zName);
+  fts3DbExec(&rc, db, "DROP TABLE IF EXISTS %Q.'%q_stat'", zDb, p->zName);
 
   /* If everything has worked, invoke fts3DisconnectMethod() to free the
   ** memory associated with the Fts3Table structure and return SQLITE_OK.
@@ -523,6 +569,10 @@ static void fts3DeclareVtab(int *pRc, Fts3Table *p){
     int rc;                       /* Return code */
     char *zSql;                   /* SQL statement passed to declare_vtab() */
     char *zCols;                  /* List of user defined columns */
+    const char *zLanguageid;
+
+    zLanguageid = (p->zLanguageid ? p->zLanguageid : "__langid");
+    sqlite3_vtab_config(p->db, SQLITE_VTAB_CONSTRAINT_SUPPORT, 1);
 
     /* Create a list of user columns for the virtual table */
     zCols = sqlite3_mprintf("%Q, ", p->azColumn[0]);
@@ -532,7 +582,8 @@ static void fts3DeclareVtab(int *pRc, Fts3Table *p){
 
     /* Create the whole "CREATE TABLE" statement to pass to SQLite */
     zSql = sqlite3_mprintf(
-        "CREATE TABLE x(%s %Q HIDDEN, docid HIDDEN)", zCols, p->zName
+        "CREATE TABLE x(%s %Q HIDDEN, docid HIDDEN, %Q HIDDEN)", 
+        zCols, p->zName, zLanguageid
     );
     if( !zCols || !zSql ){
       rc = SQLITE_NOMEM;
@@ -547,6 +598,18 @@ static void fts3DeclareVtab(int *pRc, Fts3Table *p){
 }
 
 /*
+** Create the %_stat table if it does not already exist.
+*/
+void sqlite3Fts3CreateStatTable(int *pRc, Fts3Table *p){
+  fts3DbExec(pRc, p->db, 
+      "CREATE TABLE IF NOT EXISTS %Q.'%q_stat'"
+          "(id INTEGER PRIMARY KEY, value BLOB);",
+      p->zDb, p->zName
+  );
+  if( (*pRc)==SQLITE_OK ) p->bHasStat = 1;
+}
+
+/*
 ** Create the backing store tables (%_content, %_segments and %_segdir)
 ** required by the FTS3 table passed as the only argument. This is done
 ** as part of the vtab xCreate() method.
@@ -558,23 +621,31 @@ static void fts3DeclareVtab(int *pRc, Fts3Table *p){
 static int fts3CreateTables(Fts3Table *p){
   int rc = SQLITE_OK;             /* Return code */
   int i;                          /* Iterator variable */
-  char *zContentCols;             /* Columns of %_content table */
   sqlite3 *db = p->db;            /* The database connection */
 
-  /* Create a list of user columns for the content table */
-  zContentCols = sqlite3_mprintf("docid INTEGER PRIMARY KEY");
-  for(i=0; zContentCols && i<p->nColumn; i++){
-    char *z = p->azColumn[i];
-    zContentCols = sqlite3_mprintf("%z, 'c%d%q'", zContentCols, i, z);
+  if( p->zContentTbl==0 ){
+    const char *zLanguageid = p->zLanguageid;
+    char *zContentCols;           /* Columns of %_content table */
+
+    /* Create a list of user columns for the content table */
+    zContentCols = sqlite3_mprintf("docid INTEGER PRIMARY KEY");
+    for(i=0; zContentCols && i<p->nColumn; i++){
+      char *z = p->azColumn[i];
+      zContentCols = sqlite3_mprintf("%z, 'c%d%q'", zContentCols, i, z);
+    }
+    if( zLanguageid && zContentCols ){
+      zContentCols = sqlite3_mprintf("%z, langid", zContentCols, zLanguageid);
+    }
+    if( zContentCols==0 ) rc = SQLITE_NOMEM;
+  
+    /* Create the content table */
+    fts3DbExec(&rc, db, 
+       "CREATE TABLE %Q.'%q_content'(%s)",
+       p->zDb, p->zName, zContentCols
+    );
+    sqlite3_free(zContentCols);
   }
-  if( zContentCols==0 ) rc = SQLITE_NOMEM;
 
-  /* Create the content table */
-  fts3DbExec(&rc, db, 
-     "CREATE TABLE %Q.'%q_content'(%s)",
-     p->zDb, p->zName, zContentCols
-  );
-  sqlite3_free(zContentCols);
   /* Create other tables */
   fts3DbExec(&rc, db, 
       "CREATE TABLE %Q.'%q_segments'(blockid INTEGER PRIMARY KEY, block BLOB);",
@@ -598,11 +669,9 @@ static int fts3CreateTables(Fts3Table *p){
         p->zDb, p->zName
     );
   }
+  assert( p->bHasStat==p->bFts4 );
   if( p->bHasStat ){
-    fts3DbExec(&rc, db, 
-        "CREATE TABLE %Q.'%q_stat'(id INTEGER PRIMARY KEY, value BLOB);",
-        p->zDb, p->zName
-    );
+    sqlite3Fts3CreateStatTable(&rc, p);
   }
   return rc;
 }
@@ -629,6 +698,9 @@ static void fts3DatabasePageSize(int *pRc, Fts3Table *p){
         sqlite3_step(pStmt);
         p->nPgsz = sqlite3_column_int(pStmt, 0);
         rc = sqlite3_finalize(pStmt);
+      }else if( rc==SQLITE_AUTH ){
+        p->nPgsz = 1024;
+        rc = SQLITE_OK;
       }
     }
     assert( p->nPgsz>0 || rc!=SQLITE_OK );
@@ -681,6 +753,7 @@ static void fts3Appendf(
     char *z;
     va_start(ap, zFormat);
     z = sqlite3_vmprintf(zFormat, ap);
+    va_end(ap);
     if( z && *pz ){
       char *z2 = sqlite3_mprintf("%s%s", *pz, z);
       sqlite3_free(z);
@@ -705,7 +778,7 @@ static void fts3Appendf(
 static char *fts3QuoteId(char const *zInput){
   int nRet;
   char *zRet;
-  nRet = 2 + strlen(zInput)*2 + 1;
+  nRet = 2 + (int)strlen(zInput)*2 + 1;
   zRet = sqlite3_malloc(nRet);
   if( zRet ){
     int i;
@@ -722,8 +795,8 @@ static char *fts3QuoteId(char const *zInput){
 }
 
 /*
-** Return a list of comma separated SQL expressions that could be used
-** in a SELECT statement such as the following:
+** Return a list of comma separated SQL expressions and a FROM clause that 
+** could be used in a SELECT statement such as the following:
 **
 **     SELECT <list of expressions> FROM %_content AS x ...
 **
@@ -734,7 +807,7 @@ static char *fts3QuoteId(char const *zInput){
 ** table has the three user-defined columns "a", "b", and "c", the following
 ** string is returned:
 **
-**     "docid, unzip(x.'a'), unzip(x.'b'), unzip(x.'c')"
+**     "docid, unzip(x.'a'), unzip(x.'b'), unzip(x.'c') FROM %_content AS x"
 **
 ** The pointer returned points to a buffer allocated by sqlite3_malloc(). It
 ** is the responsibility of the caller to eventually free it.
@@ -750,16 +823,34 @@ static char *fts3ReadExprList(Fts3Table *p, const char *zFunc, int *pRc){
   char *zFunction;
   int i;
 
-  if( !zFunc ){
-    zFunction = "";
+  if( p->zContentTbl==0 ){
+    if( !zFunc ){
+      zFunction = "";
+    }else{
+      zFree = zFunction = fts3QuoteId(zFunc);
+    }
+    fts3Appendf(pRc, &zRet, "docid");
+    for(i=0; i<p->nColumn; i++){
+      fts3Appendf(pRc, &zRet, ",%s(x.'c%d%q')", zFunction, i, p->azColumn[i]);
+    }
+    if( p->zLanguageid ){
+      fts3Appendf(pRc, &zRet, ", x.%Q", "langid");
+    }
+    sqlite3_free(zFree);
   }else{
-    zFree = zFunction = fts3QuoteId(zFunc);
-  }
-  fts3Appendf(pRc, &zRet, "docid");
-  for(i=0; i<p->nColumn; i++){
-    fts3Appendf(pRc, &zRet, ",%s(x.'c%d%q')", zFunction, i, p->azColumn[i]);
+    fts3Appendf(pRc, &zRet, "rowid");
+    for(i=0; i<p->nColumn; i++){
+      fts3Appendf(pRc, &zRet, ", x.'%q'", p->azColumn[i]);
+    }
+    if( p->zLanguageid ){
+      fts3Appendf(pRc, &zRet, ", x.%Q", p->zLanguageid);
+    }
   }
-  sqlite3_free(zFree);
+  fts3Appendf(pRc, &zRet, " FROM '%q'.'%q%s' AS x", 
+      p->zDb,
+      (p->zContentTbl ? p->zContentTbl : p->zName),
+      (p->zContentTbl ? "" : "_content")
+  );
   return zRet;
 }
 
@@ -798,11 +889,180 @@ static char *fts3WriteExprList(Fts3Table *p, const char *zFunc, int *pRc){
   for(i=0; i<p->nColumn; i++){
     fts3Appendf(pRc, &zRet, ",%s(?)", zFunction);
   }
+  if( p->zLanguageid ){
+    fts3Appendf(pRc, &zRet, ", ?");
+  }
   sqlite3_free(zFree);
   return zRet;
 }
 
 /*
+** This function interprets the string at (*pp) as a non-negative integer
+** value. It reads the integer and sets *pnOut to the value read, then 
+** sets *pp to point to the byte immediately following the last byte of
+** the integer value.
+**
+** Only decimal digits ('0'..'9') may be part of an integer value. 
+**
+** If *pp does not being with a decimal digit SQLITE_ERROR is returned and
+** the output value undefined. Otherwise SQLITE_OK is returned.
+**
+** This function is used when parsing the "prefix=" FTS4 parameter.
+*/
+static int fts3GobbleInt(const char **pp, int *pnOut){
+  const char *p;                  /* Iterator pointer */
+  int nInt = 0;                   /* Output value */
+
+  for(p=*pp; p[0]>='0' && p[0]<='9'; p++){
+    nInt = nInt * 10 + (p[0] - '0');
+  }
+  if( p==*pp ) return SQLITE_ERROR;
+  *pnOut = nInt;
+  *pp = p;
+  return SQLITE_OK;
+}
+
+/*
+** This function is called to allocate an array of Fts3Index structures
+** representing the indexes maintained by the current FTS table. FTS tables
+** always maintain the main "terms" index, but may also maintain one or
+** more "prefix" indexes, depending on the value of the "prefix=" parameter
+** (if any) specified as part of the CREATE VIRTUAL TABLE statement.
+**
+** Argument zParam is passed the value of the "prefix=" option if one was
+** specified, or NULL otherwise.
+**
+** If no error occurs, SQLITE_OK is returned and *apIndex set to point to
+** the allocated array. *pnIndex is set to the number of elements in the
+** array. If an error does occur, an SQLite error code is returned.
+**
+** Regardless of whether or not an error is returned, it is the responsibility
+** of the caller to call sqlite3_free() on the output array to free it.
+*/
+static int fts3PrefixParameter(
+  const char *zParam,             /* ABC in prefix=ABC parameter to parse */
+  int *pnIndex,                   /* OUT: size of *apIndex[] array */
+  struct Fts3Index **apIndex      /* OUT: Array of indexes for this table */
+){
+  struct Fts3Index *aIndex;       /* Allocated array */
+  int nIndex = 1;                 /* Number of entries in array */
+
+  if( zParam && zParam[0] ){
+    const char *p;
+    nIndex++;
+    for(p=zParam; *p; p++){
+      if( *p==',' ) nIndex++;
+    }
+  }
+
+  aIndex = sqlite3_malloc(sizeof(struct Fts3Index) * nIndex);
+  *apIndex = aIndex;
+  *pnIndex = nIndex;
+  if( !aIndex ){
+    return SQLITE_NOMEM;
+  }
+
+  memset(aIndex, 0, sizeof(struct Fts3Index) * nIndex);
+  if( zParam ){
+    const char *p = zParam;
+    int i;
+    for(i=1; i<nIndex; i++){
+      int nPrefix;
+      if( fts3GobbleInt(&p, &nPrefix) ) return SQLITE_ERROR;
+      aIndex[i].nPrefix = nPrefix;
+      p++;
+    }
+  }
+
+  return SQLITE_OK;
+}
+
+/*
+** This function is called when initializing an FTS4 table that uses the
+** content=xxx option. It determines the number of and names of the columns
+** of the new FTS4 table.
+**
+** The third argument passed to this function is the value passed to the
+** config=xxx option (i.e. "xxx"). This function queries the database for
+** a table of that name. If found, the output variables are populated
+** as follows:
+**
+**   *pnCol:   Set to the number of columns table xxx has,
+**
+**   *pnStr:   Set to the total amount of space required to store a copy
+**             of each columns name, including the nul-terminator.
+**
+**   *pazCol:  Set to point to an array of *pnCol strings. Each string is
+**             the name of the corresponding column in table xxx. The array
+**             and its contents are allocated using a single allocation. It
+**             is the responsibility of the caller to free this allocation
+**             by eventually passing the *pazCol value to sqlite3_free().
+**
+** If the table cannot be found, an error code is returned and the output
+** variables are undefined. Or, if an OOM is encountered, SQLITE_NOMEM is
+** returned (and the output variables are undefined).
+*/
+static int fts3ContentColumns(
+  sqlite3 *db,                    /* Database handle */
+  const char *zDb,                /* Name of db (i.e. "main", "temp" etc.) */
+  const char *zTbl,               /* Name of content table */
+  const char ***pazCol,           /* OUT: Malloc'd array of column names */
+  int *pnCol,                     /* OUT: Size of array *pazCol */
+  int *pnStr                      /* OUT: Bytes of string content */
+){
+  int rc = SQLITE_OK;             /* Return code */
+  char *zSql;                     /* "SELECT *" statement on zTbl */  
+  sqlite3_stmt *pStmt = 0;        /* Compiled version of zSql */
+
+  zSql = sqlite3_mprintf("SELECT * FROM %Q.%Q", zDb, zTbl);
+  if( !zSql ){
+    rc = SQLITE_NOMEM;
+  }else{
+    rc = sqlite3_prepare(db, zSql, -1, &pStmt, 0);
+  }
+  sqlite3_free(zSql);
+
+  if( rc==SQLITE_OK ){
+    const char **azCol;           /* Output array */
+    int nStr = 0;                 /* Size of all column names (incl. 0x00) */
+    int nCol;                     /* Number of table columns */
+    int i;                        /* Used to iterate through columns */
+
+    /* Loop through the returned columns. Set nStr to the number of bytes of
+    ** space required to store a copy of each column name, including the
+    ** nul-terminator byte.  */
+    nCol = sqlite3_column_count(pStmt);
+    for(i=0; i<nCol; i++){
+      const char *zCol = sqlite3_column_name(pStmt, i);
+      nStr += (int)strlen(zCol) + 1;
+    }
+
+    /* Allocate and populate the array to return. */
+    azCol = (const char **)sqlite3_malloc(sizeof(char *) * nCol + nStr);
+    if( azCol==0 ){
+      rc = SQLITE_NOMEM;
+    }else{
+      char *p = (char *)&azCol[nCol];
+      for(i=0; i<nCol; i++){
+        const char *zCol = sqlite3_column_name(pStmt, i);
+        int n = (int)strlen(zCol)+1;
+        memcpy(p, zCol, n);
+        azCol[i] = p;
+        p += n;
+      }
+    }
+    sqlite3_finalize(pStmt);
+
+    /* Set the output variables. */
+    *pnCol = nCol;
+    *pnStr = nStr;
+    *pazCol = azCol;
+  }
+
+  return rc;
+}
+
+/*
 ** This function is the implementation of both the xConnect and xCreate
 ** methods of the FTS3 virtual table.
 **
@@ -834,12 +1094,22 @@ static int fts3InitVtab(
   int nDb;                        /* Bytes required to hold database name */
   int nName;                      /* Bytes required to hold table name */
   int isFts4 = (argv[0][3]=='4'); /* True for FTS4, false for FTS3 */
-  int bNoDocsize = 0;             /* True to omit %_docsize table */
   const char **aCol;              /* Array of column names */
   sqlite3_tokenizer *pTokenizer = 0;        /* Tokenizer for this table */
 
-  char *zCompress = 0;
-  char *zUncompress = 0;
+  int nIndex;                     /* Size of aIndex[] array */
+  struct Fts3Index *aIndex = 0;   /* Array of indexes for this table */
+
+  /* The results of parsing supported FTS4 key=value options: */
+  int bNoDocsize = 0;             /* True to omit %_docsize table */
+  int bDescIdx = 0;               /* True to store descending indexes */
+  char *zPrefix = 0;              /* Prefix parameter value (or NULL) */
+  char *zCompress = 0;            /* compress=? parameter (or NULL) */
+  char *zUncompress = 0;          /* uncompress=? parameter (or NULL) */
+  char *zContent = 0;             /* content=? parameter (or NULL) */
+  char *zLanguageid = 0;          /* languageid=? parameter (or NULL) */
+  char **azNotindexed = 0;        /* The set of notindexed= columns */
+  int nNotindexed = 0;            /* Size of azNotindexed[] array */
 
   assert( strlen(argv[0])==4 );
   assert( (sqlite3_strnicmp(argv[0], "fts4", 4)==0 && isFts4)
@@ -849,9 +1119,19 @@ static int fts3InitVtab(
   nDb = (int)strlen(argv[1]) + 1;
   nName = (int)strlen(argv[2]) + 1;
 
-  aCol = (const char **)sqlite3_malloc(sizeof(const char *) * (argc-2) );
-  if( !aCol ) return SQLITE_NOMEM;
-  memset((void *)aCol, 0, sizeof(const char *) * (argc-2));
+  nByte = sizeof(const char *) * (argc-2);
+  aCol = (const char **)sqlite3_malloc(nByte);
+  if( aCol ){
+    memset((void*)aCol, 0, nByte);
+    azNotindexed = (char **)sqlite3_malloc(nByte);
+  }
+  if( azNotindexed ){
+    memset(azNotindexed, 0, nByte);
+  }
+  if( !aCol || !azNotindexed ){
+    rc = SQLITE_NOMEM;
+    goto fts3_init_out;
+  }
 
   /* Loop through all of the arguments passed by the user to the FTS3/4
   ** module (i.e. all the column names and special arguments). This loop
@@ -880,28 +1160,92 @@ static int fts3InitVtab(
 
     /* Check if it is an FTS4 special argument. */
     else if( isFts4 && fts3IsSpecialColumn(z, &nKey, &zVal) ){
+      struct Fts4Option {
+        const char *zOpt;
+        int nOpt;
+      } aFts4Opt[] = {
+        { "matchinfo",   9 },     /* 0 -> MATCHINFO */
+        { "prefix",      6 },     /* 1 -> PREFIX */
+        { "compress",    8 },     /* 2 -> COMPRESS */
+        { "uncompress", 10 },     /* 3 -> UNCOMPRESS */
+        { "order",       5 },     /* 4 -> ORDER */
+        { "content",     7 },     /* 5 -> CONTENT */
+        { "languageid", 10 },     /* 6 -> LANGUAGEID */
+        { "notindexed", 10 }      /* 7 -> NOTINDEXED */
+      };
+
+      int iOpt;
       if( !zVal ){
         rc = SQLITE_NOMEM;
-        goto fts3_init_out;
-      }
-      if( nKey==9 && 0==sqlite3_strnicmp(z, "matchinfo", 9) ){
-        if( strlen(zVal)==4 && 0==sqlite3_strnicmp(zVal, "fts3", 4) ){
-          bNoDocsize = 1;
-        }else{
-          *pzErr = sqlite3_mprintf("unrecognized matchinfo: %s", zVal);
+      }else{
+        for(iOpt=0; iOpt<SizeofArray(aFts4Opt); iOpt++){
+          struct Fts4Option *pOp = &aFts4Opt[iOpt];
+          if( nKey==pOp->nOpt && !sqlite3_strnicmp(z, pOp->zOpt, pOp->nOpt) ){
+            break;
+          }
+        }
+        if( iOpt==SizeofArray(aFts4Opt) ){
+          *pzErr = sqlite3_mprintf("unrecognized parameter: %s", z);
           rc = SQLITE_ERROR;
+        }else{
+          switch( iOpt ){
+            case 0:               /* MATCHINFO */
+              if( strlen(zVal)!=4 || sqlite3_strnicmp(zVal, "fts3", 4) ){
+                *pzErr = sqlite3_mprintf("unrecognized matchinfo: %s", zVal);
+                rc = SQLITE_ERROR;
+              }
+              bNoDocsize = 1;
+              break;
+
+            case 1:               /* PREFIX */
+              sqlite3_free(zPrefix);
+              zPrefix = zVal;
+              zVal = 0;
+              break;
+
+            case 2:               /* COMPRESS */
+              sqlite3_free(zCompress);
+              zCompress = zVal;
+              zVal = 0;
+              break;
+
+            case 3:               /* UNCOMPRESS */
+              sqlite3_free(zUncompress);
+              zUncompress = zVal;
+              zVal = 0;
+              break;
+
+            case 4:               /* ORDER */
+              if( (strlen(zVal)!=3 || sqlite3_strnicmp(zVal, "asc", 3)) 
+               && (strlen(zVal)!=4 || sqlite3_strnicmp(zVal, "desc", 4)) 
+              ){
+                *pzErr = sqlite3_mprintf("unrecognized order: %s", zVal);
+                rc = SQLITE_ERROR;
+              }
+              bDescIdx = (zVal[0]=='d' || zVal[0]=='D');
+              break;
+
+            case 5:              /* CONTENT */
+              sqlite3_free(zContent);
+              zContent = zVal;
+              zVal = 0;
+              break;
+
+            case 6:              /* LANGUAGEID */
+              assert( iOpt==6 );
+              sqlite3_free(zLanguageid);
+              zLanguageid = zVal;
+              zVal = 0;
+              break;
+
+            case 7:              /* NOTINDEXED */
+              azNotindexed[nNotindexed++] = zVal;
+              zVal = 0;
+              break;
+          }
         }
-      }else if( nKey==8 && 0==sqlite3_strnicmp(z, "compress", 8) ){
-        zCompress = zVal;
-        zVal = 0;
-      }else if( nKey==10 && 0==sqlite3_strnicmp(z, "uncompress", 10) ){
-        zUncompress = zVal;
-        zVal = 0;
-      }else{
-        *pzErr = sqlite3_mprintf("unrecognized parameter: %s", z);
-        rc = SQLITE_ERROR;
+        sqlite3_free(zVal);
       }
-      sqlite3_free(zVal);
     }
 
     /* Otherwise, the argument is a column name. */
@@ -910,6 +1254,39 @@ static int fts3InitVtab(
       aCol[nCol++] = z;
     }
   }
+
+  /* If a content=xxx option was specified, the following:
+  **
+  **   1. Ignore any compress= and uncompress= options.
+  **
+  **   2. If no column names were specified as part of the CREATE VIRTUAL
+  **      TABLE statement, use all columns from the content table.
+  */
+  if( rc==SQLITE_OK && zContent ){
+    sqlite3_free(zCompress); 
+    sqlite3_free(zUncompress); 
+    zCompress = 0;
+    zUncompress = 0;
+    if( nCol==0 ){
+      sqlite3_free((void*)aCol); 
+      aCol = 0;
+      rc = fts3ContentColumns(db, argv[1], zContent, &aCol, &nCol, &nString);
+
+      /* If a languageid= option was specified, remove the language id
+      ** column from the aCol[] array. */ 
+      if( rc==SQLITE_OK && zLanguageid ){
+        int j;
+        for(j=0; j<nCol; j++){
+          if( sqlite3_stricmp(zLanguageid, aCol[j])==0 ){
+            int k;
+            for(k=j; k<nCol; k++) aCol[k] = aCol[k+1];
+            nCol--;
+            break;
+          }
+        }
+      }
+    }
+  }
   if( rc!=SQLITE_OK ) goto fts3_init_out;
 
   if( nCol==0 ){
@@ -925,10 +1302,18 @@ static int fts3InitVtab(
   }
   assert( pTokenizer );
 
+  rc = fts3PrefixParameter(zPrefix, &nIndex, &aIndex);
+  if( rc==SQLITE_ERROR ){
+    assert( zPrefix );
+    *pzErr = sqlite3_mprintf("error parsing prefix parameter: %s", zPrefix);
+  }
+  if( rc!=SQLITE_OK ) goto fts3_init_out;
 
   /* Allocate and populate the Fts3Table structure. */
-  nByte = sizeof(Fts3Table) +              /* Fts3Table */
+  nByte = sizeof(Fts3Table) +                  /* Fts3Table */
           nCol * sizeof(char *) +              /* azColumn */
+          nIndex * sizeof(struct Fts3Index) +  /* aIndex */
+          nCol * sizeof(u8) +                  /* abNotindexed */
           nName +                              /* zName */
           nDb +                                /* zDb */
           nString;                             /* Space for azColumn strings */
@@ -943,14 +1328,29 @@ static int fts3InitVtab(
   p->nPendingData = 0;
   p->azColumn = (char **)&p[1];
   p->pTokenizer = pTokenizer;
-  p->nNodeSize = 1000;
   p->nMaxPendingData = FTS3_MAX_PENDING_DATA;
   p->bHasDocsize = (isFts4 && bNoDocsize==0);
   p->bHasStat = isFts4;
-  fts3HashInit(&p->pendingTerms, FTS3_HASH_STRING, 1);
+  p->bFts4 = isFts4;
+  p->bDescIdx = bDescIdx;
+  p->bAutoincrmerge = 0xff;   /* 0xff means setting unknown */
+  p->zContentTbl = zContent;
+  p->zLanguageid = zLanguageid;
+  zContent = 0;
+  zLanguageid = 0;
+  TESTONLY( p->inTransaction = -1 );
+  TESTONLY( p->mxSavepoint = -1 );
+
+  p->aIndex = (struct Fts3Index *)&p->azColumn[nCol];
+  memcpy(p->aIndex, aIndex, sizeof(struct Fts3Index) * nIndex);
+  p->nIndex = nIndex;
+  for(i=0; i<nIndex; i++){
+    fts3HashInit(&p->aIndex[i].hPending, FTS3_HASH_STRING, 1);
+  }
+  p->abNotindexed = (u8 *)&p->aIndex[nIndex];
 
   /* Fill in the zName and zDb fields of the vtab structure. */
-  zCsr = (char *)&p->azColumn[nCol];
+  zCsr = (char *)&p->abNotindexed[nCol];
   p->zName = zCsr;
   memcpy(zCsr, argv[2], nName);
   zCsr += nName;
@@ -961,7 +1361,7 @@ static int fts3InitVtab(
   /* Fill in the azColumn array */
   for(iCol=0; iCol<nCol; iCol++){
     char *z; 
-    int n;
+    int n = 0;
     z = (char *)sqlite3Fts3NextToken(aCol[iCol], &n);
     memcpy(zCsr, z, n);
     zCsr[n] = '\0';
@@ -971,7 +1371,26 @@ static int fts3InitVtab(
     assert( zCsr <= &((char *)p)[nByte] );
   }
 
-  if( (zCompress==0)!=(zUncompress==0) ){
+  /* Fill in the abNotindexed array */
+  for(iCol=0; iCol<nCol; iCol++){
+    int n = (int)strlen(p->azColumn[iCol]);
+    for(i=0; i<nNotindexed; i++){
+      char *zNot = azNotindexed[i];
+      if( zNot && 0==sqlite3_strnicmp(p->azColumn[iCol], zNot, n) ){
+        p->abNotindexed[iCol] = 1;
+        sqlite3_free(zNot);
+        azNotindexed[i] = 0;
+      }
+    }
+  }
+  for(i=0; i<nNotindexed; i++){
+    if( azNotindexed[i] ){
+      *pzErr = sqlite3_mprintf("no such column: %s", azNotindexed[i]);
+      rc = SQLITE_ERROR;
+    }
+  }
+
+  if( rc==SQLITE_OK && (zCompress==0)!=(zUncompress==0) ){
     char const *zMiss = (zCompress==0 ? "compress" : "uncompress");
     rc = SQLITE_ERROR;
     *pzErr = sqlite3_mprintf("missing %s parameter in fts4 constructor", zMiss);
@@ -987,19 +1406,34 @@ static int fts3InitVtab(
     rc = fts3CreateTables(p);
   }
 
-  /* Figure out the page-size for the database. This is required in order to
-  ** estimate the cost of loading large doclists from the database (see 
-  ** function sqlite3Fts3SegReaderCost() for details).
+  /* Check to see if a legacy fts3 table has been "upgraded" by the
+  ** addition of a %_stat table so that it can use incremental merge.
   */
+  if( !isFts4 && !isCreate ){
+    int rc2 = SQLITE_OK;
+    fts3DbExec(&rc2, db, "SELECT 1 FROM %Q.'%q_stat' WHERE id=2",
+               p->zDb, p->zName);
+    if( rc2==SQLITE_OK ) p->bHasStat = 1;
+  }
+
+  /* Figure out the page-size for the database. This is required in order to
+  ** estimate the cost of loading large doclists from the database.  */
   fts3DatabasePageSize(&rc, p);
+  p->nNodeSize = p->nPgsz-35;
 
   /* Declare the table schema to SQLite. */
   fts3DeclareVtab(&rc, p);
 
 fts3_init_out:
+  sqlite3_free(zPrefix);
+  sqlite3_free(aIndex);
   sqlite3_free(zCompress);
   sqlite3_free(zUncompress);
+  sqlite3_free(zContent);
+  sqlite3_free(zLanguageid);
+  for(i=0; i<nNotindexed; i++) sqlite3_free(azNotindexed[i]);
   sqlite3_free((void *)aCol);
+  sqlite3_free((void *)azNotindexed);
   if( rc!=SQLITE_OK ){
     if( p ){
       fts3DisconnectMethod((sqlite3_vtab *)p);
@@ -1007,6 +1441,7 @@ fts3_init_out:
       pTokenizer->pModule->xDestroy(pTokenizer);
     }
   }else{
+    assert( p->pSegments==0 );
     *ppVTab = &p->base;
   }
   return rc;
@@ -1037,6 +1472,19 @@ static int fts3CreateMethod(
   return fts3InitVtab(1, db, pAux, argc, argv, ppVtab, pzErr);
 }
 
+/*
+** Set the pIdxInfo->estimatedRows variable to nRow. Unless this
+** extension is currently being used by a version of SQLite too old to
+** support estimatedRows. In that case this function is a no-op.
+*/
+static void fts3SetEstimatedRows(sqlite3_index_info *pIdxInfo, i64 nRow){
+#if SQLITE_VERSION_NUMBER>=3008002
+  if( sqlite3_libversion_number()>=3008002 ){
+    pIdxInfo->estimatedRows = nRow;
+  }
+#endif
+}
+
 /* 
 ** Implementation of the xBestIndex method for FTS3 tables. There
 ** are three possible strategies, in order of preference:
@@ -1050,20 +1498,39 @@ static int fts3BestIndexMethod(sqlite3_vtab *pVTab, sqlite3_index_info *pInfo){
   int i;                          /* Iterator variable */
   int iCons = -1;                 /* Index of constraint to use */
 
+  int iLangidCons = -1;           /* Index of langid=x constraint, if present */
+  int iDocidGe = -1;              /* Index of docid>=x constraint, if present */
+  int iDocidLe = -1;              /* Index of docid<=x constraint, if present */
+  int iIdx;
+
   /* By default use a full table scan. This is an expensive option,
   ** so search through the constraints to see if a more efficient 
   ** strategy is possible.
   */
   pInfo->idxNum = FTS3_FULLSCAN_SEARCH;
-  pInfo->estimatedCost = 500000;
+  pInfo->estimatedCost = 5000000;
   for(i=0; i<pInfo->nConstraint; i++){
+    int bDocid;                 /* True if this constraint is on docid */
     struct sqlite3_index_constraint *pCons = &pInfo->aConstraint[i];
-    if( pCons->usable==0 ) continue;
+    if( pCons->usable==0 ){
+      if( pCons->op==SQLITE_INDEX_CONSTRAINT_MATCH ){
+        /* There exists an unusable MATCH constraint. This means that if
+        ** the planner does elect to use the results of this call as part
+        ** of the overall query plan the user will see an "unable to use
+        ** function MATCH in the requested context" error. To discourage
+        ** this, return a very high cost here.  */
+        pInfo->idxNum = FTS3_FULLSCAN_SEARCH;
+        pInfo->estimatedCost = 1e50;
+        fts3SetEstimatedRows(pInfo, ((sqlite3_int64)1) << 50);
+        return SQLITE_OK;
+      }
+      continue;
+    }
+
+    bDocid = (pCons->iColumn<0 || pCons->iColumn==p->nColumn+1);
 
     /* A direct lookup on the rowid or docid column. Assign a cost of 1.0. */
-    if( pCons->op==SQLITE_INDEX_CONSTRAINT_EQ 
-     && (pCons->iColumn<0 || pCons->iColumn==p->nColumn+1 )
-    ){
+    if( iCons<0 && pCons->op==SQLITE_INDEX_CONSTRAINT_EQ && bDocid ){
       pInfo->idxNum = FTS3_DOCID_SEARCH;
       pInfo->estimatedCost = 1.0;
       iCons = i;
@@ -1084,14 +1551,64 @@ static int fts3BestIndexMethod(sqlite3_vtab *pVTab, sqlite3_index_info *pInfo){
       pInfo->idxNum = FTS3_FULLTEXT_SEARCH + pCons->iColumn;
       pInfo->estimatedCost = 2.0;
       iCons = i;
-      break;
+    }
+
+    /* Equality constraint on the langid column */
+    if( pCons->op==SQLITE_INDEX_CONSTRAINT_EQ 
+     && pCons->iColumn==p->nColumn + 2
+    ){
+      iLangidCons = i;
+    }
+
+    if( bDocid ){
+      switch( pCons->op ){
+        case SQLITE_INDEX_CONSTRAINT_GE:
+        case SQLITE_INDEX_CONSTRAINT_GT:
+          iDocidGe = i;
+          break;
+
+        case SQLITE_INDEX_CONSTRAINT_LE:
+        case SQLITE_INDEX_CONSTRAINT_LT:
+          iDocidLe = i;
+          break;
+      }
     }
   }
 
+  iIdx = 1;
   if( iCons>=0 ){
-    pInfo->aConstraintUsage[iCons].argvIndex = 1;
+    pInfo->aConstraintUsage[iCons].argvIndex = iIdx++;
     pInfo->aConstraintUsage[iCons].omit = 1;
   } 
+  if( iLangidCons>=0 ){
+    pInfo->idxNum |= FTS3_HAVE_LANGID;
+    pInfo->aConstraintUsage[iLangidCons].argvIndex = iIdx++;
+  } 
+  if( iDocidGe>=0 ){
+    pInfo->idxNum |= FTS3_HAVE_DOCID_GE;
+    pInfo->aConstraintUsage[iDocidGe].argvIndex = iIdx++;
+  } 
+  if( iDocidLe>=0 ){
+    pInfo->idxNum |= FTS3_HAVE_DOCID_LE;
+    pInfo->aConstraintUsage[iDocidLe].argvIndex = iIdx++;
+  } 
+
+  /* Regardless of the strategy selected, FTS can deliver rows in rowid (or
+  ** docid) order. Both ascending and descending are possible. 
+  */
+  if( pInfo->nOrderBy==1 ){
+    struct sqlite3_index_orderby *pOrder = &pInfo->aOrderBy[0];
+    if( pOrder->iColumn<0 || pOrder->iColumn==p->nColumn+1 ){
+      if( pOrder->desc ){
+        pInfo->idxStr = "DESC";
+      }else{
+        pInfo->idxStr = "ASC";
+      }
+      pInfo->orderByConsumed = 1;
+    }
+  }
+
+  assert( p->pSegments==0 );
   return SQLITE_OK;
 }
 
@@ -1127,39 +1644,69 @@ static int fts3CloseMethod(sqlite3_vtab_cursor *pCursor){
   sqlite3Fts3FreeDeferredTokens(pCsr);
   sqlite3_free(pCsr->aDoclist);
   sqlite3_free(pCsr->aMatchinfo);
+  assert( ((Fts3Table *)pCsr->base.pVtab)->pSegments==0 );
   sqlite3_free(pCsr);
   return SQLITE_OK;
 }
 
 /*
+** If pCsr->pStmt has not been prepared (i.e. if pCsr->pStmt==0), then
+** compose and prepare an SQL statement of the form:
+**
+**    "SELECT <columns> FROM %_content WHERE rowid = ?"
+**
+** (or the equivalent for a content=xxx table) and set pCsr->pStmt to
+** it. If an error occurs, return an SQLite error code.
+**
+** Otherwise, set *ppStmt to point to pCsr->pStmt and return SQLITE_OK.
+*/
+static int fts3CursorSeekStmt(Fts3Cursor *pCsr, sqlite3_stmt **ppStmt){
+  int rc = SQLITE_OK;
+  if( pCsr->pStmt==0 ){
+    Fts3Table *p = (Fts3Table *)pCsr->base.pVtab;
+    char *zSql;
+    zSql = sqlite3_mprintf("SELECT %s WHERE rowid = ?", p->zReadExprlist);
+    if( !zSql ) return SQLITE_NOMEM;
+    rc = sqlite3_prepare_v2(p->db, zSql, -1, &pCsr->pStmt, 0);
+    sqlite3_free(zSql);
+  }
+  *ppStmt = pCsr->pStmt;
+  return rc;
+}
+
+/*
 ** Position the pCsr->pStmt statement so that it is on the row
 ** of the %_content table that contains the last match.  Return
 ** SQLITE_OK on success.  
 */
 static int fts3CursorSeek(sqlite3_context *pContext, Fts3Cursor *pCsr){
+  int rc = SQLITE_OK;
   if( pCsr->isRequireSeek ){
-    pCsr->isRequireSeek = 0;
-    sqlite3_bind_int64(pCsr->pStmt, 1, pCsr->iPrevId);
-    if( SQLITE_ROW==sqlite3_step(pCsr->pStmt) ){
-      return SQLITE_OK;
-    }else{
-      int rc = sqlite3_reset(pCsr->pStmt);
-      if( rc==SQLITE_OK ){
-        /* If no row was found and no error has occured, then the %_content
-        ** table is missing a row that is present in the full-text index.
-        ** The data structures are corrupt.
-        */
-        rc = SQLITE_CORRUPT;
-      }
-      pCsr->isEof = 1;
-      if( pContext ){
-        sqlite3_result_error_code(pContext, rc);
+    sqlite3_stmt *pStmt = 0;
+
+    rc = fts3CursorSeekStmt(pCsr, &pStmt);
+    if( rc==SQLITE_OK ){
+      sqlite3_bind_int64(pCsr->pStmt, 1, pCsr->iPrevId);
+      pCsr->isRequireSeek = 0;
+      if( SQLITE_ROW==sqlite3_step(pCsr->pStmt) ){
+        return SQLITE_OK;
+      }else{
+        rc = sqlite3_reset(pCsr->pStmt);
+        if( rc==SQLITE_OK && ((Fts3Table *)pCsr->base.pVtab)->zContentTbl==0 ){
+          /* If no row was found and no error has occurred, then the %_content
+          ** table is missing a row that is present in the full-text index.
+          ** The data structures are corrupt.  */
+          rc = FTS_CORRUPT_VTAB;
+          pCsr->isEof = 1;
+        }
       }
-      return rc;
     }
-  }else{
-    return SQLITE_OK;
   }
+
+  if( rc!=SQLITE_OK && pContext ){
+    sqlite3_result_error_code(pContext, rc);
+  }
+  return rc;
 }
 
 /*
@@ -1209,7 +1756,7 @@ static int fts3ScanInteriorNode(
   zCsr += sqlite3Fts3GetVarint(zCsr, &iChild);
   zCsr += sqlite3Fts3GetVarint(zCsr, &iChild);
   if( zCsr>zEnd ){
-    return SQLITE_CORRUPT;
+    return FTS_CORRUPT_VTAB;
   }
   
   while( zCsr<zEnd && (piFirst || piLast) ){
@@ -1221,13 +1768,13 @@ static int fts3ScanInteriorNode(
     /* Load the next term on the node into zBuffer. Use realloc() to expand
     ** the size of zBuffer if required.  */
     if( !isFirstTerm ){
-      zCsr += sqlite3Fts3GetVarint32(zCsr, &nPrefix);
+      zCsr += fts3GetVarint32(zCsr, &nPrefix);
     }
     isFirstTerm = 0;
-    zCsr += sqlite3Fts3GetVarint32(zCsr, &nSuffix);
+    zCsr += fts3GetVarint32(zCsr, &nSuffix);
     
     if( nPrefix<0 || nSuffix<0 || &zCsr[nSuffix]>zEnd ){
-      rc = SQLITE_CORRUPT;
+      rc = FTS_CORRUPT_VTAB;
       goto finish_scan;
     }
     if( nPrefix+nSuffix>nAlloc ){
@@ -1240,6 +1787,7 @@ static int fts3ScanInteriorNode(
       }
       zBuffer = zNew;
     }
+    assert( zBuffer );
     memcpy(&zBuffer[nPrefix], zCsr, nSuffix);
     nBuffer = nPrefix + nSuffix;
     zCsr += nSuffix;
@@ -1311,7 +1859,7 @@ static int fts3SelectLeaf(
 
   assert( piLeaf || piLeaf2 );
 
-  sqlite3Fts3GetVarint32(zNode, &iHeight);
+  fts3GetVarint32(zNode, &iHeight);
   rc = fts3ScanInteriorNode(zTerm, nTerm, zNode, nNode, piLeaf, piLeaf2);
   assert( !piLeaf2 || !piLeaf || rc!=SQLITE_OK || (*piLeaf<=*piLeaf2) );
 
@@ -1320,7 +1868,7 @@ static int fts3SelectLeaf(
     int nBlob;                    /* Size of zBlob in bytes */
 
     if( piLeaf && piLeaf2 && (*piLeaf!=*piLeaf2) ){
-      rc = sqlite3Fts3ReadBlock(p, *piLeaf, &zBlob, &nBlob);
+      rc = sqlite3Fts3ReadBlock(p, *piLeaf, &zBlob, &nBlob, 0);
       if( rc==SQLITE_OK ){
         rc = fts3SelectLeaf(p, zTerm, nTerm, zBlob, nBlob, piLeaf, 0);
       }
@@ -1330,7 +1878,7 @@ static int fts3SelectLeaf(
     }
 
     if( rc==SQLITE_OK ){
-      rc = sqlite3Fts3ReadBlock(p, piLeaf ? *piLeaf : *piLeaf2, &zBlob, &nBlob);
+      rc = sqlite3Fts3ReadBlock(p, piLeaf?*piLeaf:*piLeaf2, &zBlob, &nBlob, 0);
     }
     if( rc==SQLITE_OK ){
       rc = fts3SelectLeaf(p, zTerm, nTerm, zBlob, nBlob, piLeaf, piLeaf2);
@@ -1513,11 +2061,11 @@ static void fts3PoslistMerge(
     int iCol1;         /* The current column index in pp1 */
     int iCol2;         /* The current column index in pp2 */
 
-    if( *p1==POS_COLUMN ) sqlite3Fts3GetVarint32(&p1[1], &iCol1);
+    if( *p1==POS_COLUMN ) fts3GetVarint32(&p1[1], &iCol1);
     else if( *p1==POS_END ) iCol1 = POSITION_LIST_END;
     else iCol1 = 0;
 
-    if( *p2==POS_COLUMN ) sqlite3Fts3GetVarint32(&p2[1], &iCol2);
+    if( *p2==POS_COLUMN ) fts3GetVarint32(&p2[1], &iCol2);
     else if( *p2==POS_END ) iCol2 = POSITION_LIST_END;
     else iCol2 = 0;
 
@@ -1568,8 +2116,6 @@ static void fts3PoslistMerge(
 }
 
 /*
-** nToken==1 searches for adjacent positions.
-**
 ** This function is used to merge two position lists into one. When it is
 ** called, *pp1 and *pp2 must both point to position lists. A position-list is
 ** the part of a doclist that follows each document id. For example, if a row
@@ -1589,6 +2135,8 @@ static void fts3PoslistMerge(
 ** *pp1 so that (pos(*pp2)>pos(*pp1) && pos(*pp2)-pos(*pp1)<=nToken). i.e.
 ** when the *pp1 token appears before the *pp2 token, but not more than nToken
 ** slots before it.
+**
+** e.g. nToken==1 searches for adjacent positions.
 */
 static int fts3PoslistPhraseMerge(
   char **pp,                      /* IN/OUT: Preallocated output buffer */
@@ -1598,7 +2146,7 @@ static int fts3PoslistPhraseMerge(
   char **pp1,                     /* IN/OUT: Left input list */
   char **pp2                      /* IN/OUT: Right input list */
 ){
-  char *p = (pp ? *pp : 0);
+  char *p = *pp;
   char *p1 = *pp1;
   char *p2 = *pp2;
   int iCol1 = 0;
@@ -1607,14 +2155,14 @@ static int fts3PoslistPhraseMerge(
   /* Never set both isSaveLeft and isExact for the same invocation. */
   assert( isSaveLeft==0 || isExact==0 );
 
-  assert( *p1!=0 && *p2!=0 );
+  assert( p!=0 && *p1!=0 && *p2!=0 );
   if( *p1==POS_COLUMN ){ 
     p1++;
-    p1 += sqlite3Fts3GetVarint32(p1, &iCol1);
+    p1 += fts3GetVarint32(p1, &iCol1);
   }
   if( *p2==POS_COLUMN ){ 
     p2++;
-    p2 += sqlite3Fts3GetVarint32(p2, &iCol2);
+    p2 += fts3GetVarint32(p2, &iCol2);
   }
 
   while( 1 ){
@@ -1624,7 +2172,7 @@ static int fts3PoslistPhraseMerge(
       sqlite3_int64 iPos1 = 0;
       sqlite3_int64 iPos2 = 0;
 
-      if( pp && iCol1 ){
+      if( iCol1 ){
         *p++ = POS_COLUMN;
         p += sqlite3Fts3PutVarint(p, iCol1);
       }
@@ -1639,16 +2187,10 @@ static int fts3PoslistPhraseMerge(
          || (isExact==0 && iPos2>iPos1 && iPos2<=iPos1+nToken) 
         ){
           sqlite3_int64 iSave;
-          if( !pp ){
-            fts3PoslistCopy(0, &p2);
-            fts3PoslistCopy(0, &p1);
-            *pp1 = p1;
-            *pp2 = p2;
-            return 1;
-          }
           iSave = isSaveLeft ? iPos1 : iPos2;
           fts3PutDeltaVarint(&p, &iPrev, iSave+2); iPrev -= 2;
           pSave = 0;
+          assert( p );
         }
         if( (!isSaveLeft && iPos2<=(iPos1+nToken)) || iPos2<=iPos1 ){
           if( (*p2&0xFE)==0 ) break;
@@ -1670,9 +2212,9 @@ static int fts3PoslistPhraseMerge(
       if( 0==*p1 || 0==*p2 ) break;
 
       p1++;
-      p1 += sqlite3Fts3GetVarint32(p1, &iCol1);
+      p1 += fts3GetVarint32(p1, &iCol1);
       p2++;
-      p2 += sqlite3Fts3GetVarint32(p2, &iCol2);
+      p2 += fts3GetVarint32(p2, &iCol2);
     }
 
     /* Advance pointer p1 or p2 (whichever corresponds to the smaller of
@@ -1684,12 +2226,12 @@ static int fts3PoslistPhraseMerge(
       fts3ColumnlistCopy(0, &p1);
       if( 0==*p1 ) break;
       p1++;
-      p1 += sqlite3Fts3GetVarint32(p1, &iCol1);
+      p1 += fts3GetVarint32(p1, &iCol1);
     }else{
       fts3ColumnlistCopy(0, &p2);
       if( 0==*p2 ) break;
       p2++;
-      p2 += sqlite3Fts3GetVarint32(p2, &iCol2);
+      p2 += fts3GetVarint32(p2, &iCol2);
     }
   }
 
@@ -1697,7 +2239,7 @@ static int fts3PoslistPhraseMerge(
   fts3PoslistCopy(0, &p1);
   *pp1 = p1;
   *pp2 = p2;
-  if( !pp || *pp==p ){
+  if( *pp==p ){
     return 0;
   }
   *p++ = 0x00;
@@ -1706,7 +2248,19 @@ static int fts3PoslistPhraseMerge(
 }
 
 /*
-** Merge two position-lists as required by the NEAR operator.
+** Merge two position-lists as required by the NEAR operator. The argument
+** position lists correspond to the left and right phrases of an expression 
+** like:
+**
+**     "phrase 1" NEAR "phrase number 2"
+**
+** Position list *pp1 corresponds to the left-hand side of the NEAR 
+** expression and *pp2 to the right. As usual, the indexes in the position 
+** lists are the offsets of the last token in each phrase (tokens "1" and "2" 
+** in the example above).
+**
+** The output position list - written to *pp - is a copy of *pp2 with those
+** entries that are not sufficiently NEAR entries in *pp1 removed.
 */
 static int fts3PoslistNearMerge(
   char **pp,                      /* Output buffer */
@@ -1719,226 +2273,325 @@ static int fts3PoslistNearMerge(
   char *p1 = *pp1;
   char *p2 = *pp2;
 
-  if( !pp ){
-    if( fts3PoslistPhraseMerge(0, nRight, 0, 0, pp1, pp2) ) return 1;
-    *pp1 = p1;
-    *pp2 = p2;
-    return fts3PoslistPhraseMerge(0, nLeft, 0, 0, pp2, pp1);
+  char *pTmp1 = aTmp;
+  char *pTmp2;
+  char *aTmp2;
+  int res = 1;
+
+  fts3PoslistPhraseMerge(&pTmp1, nRight, 0, 0, pp1, pp2);
+  aTmp2 = pTmp2 = pTmp1;
+  *pp1 = p1;
+  *pp2 = p2;
+  fts3PoslistPhraseMerge(&pTmp2, nLeft, 1, 0, pp2, pp1);
+  if( pTmp1!=aTmp && pTmp2!=aTmp2 ){
+    fts3PoslistMerge(pp, &aTmp, &aTmp2);
+  }else if( pTmp1!=aTmp ){
+    fts3PoslistCopy(pp, &aTmp);
+  }else if( pTmp2!=aTmp2 ){
+    fts3PoslistCopy(pp, &aTmp2);
+  }else{
+    res = 0;
+  }
+
+  return res;
+}
+
+/* 
+** An instance of this function is used to merge together the (potentially
+** large number of) doclists for each term that matches a prefix query.
+** See function fts3TermSelectMerge() for details.
+*/
+typedef struct TermSelect TermSelect;
+struct TermSelect {
+  char *aaOutput[16];             /* Malloc'd output buffers */
+  int anOutput[16];               /* Size each output buffer in bytes */
+};
+
+/*
+** This function is used to read a single varint from a buffer. Parameter
+** pEnd points 1 byte past the end of the buffer. When this function is
+** called, if *pp points to pEnd or greater, then the end of the buffer
+** has been reached. In this case *pp is set to 0 and the function returns.
+**
+** If *pp does not point to or past pEnd, then a single varint is read
+** from *pp. *pp is then set to point 1 byte past the end of the read varint.
+**
+** If bDescIdx is false, the value read is added to *pVal before returning.
+** If it is true, the value read is subtracted from *pVal before this 
+** function returns.
+*/
+static void fts3GetDeltaVarint3(
+  char **pp,                      /* IN/OUT: Point to read varint from */
+  char *pEnd,                     /* End of buffer */
+  int bDescIdx,                   /* True if docids are descending */
+  sqlite3_int64 *pVal             /* IN/OUT: Integer value */
+){
+  if( *pp>=pEnd ){
+    *pp = 0;
   }else{
-    char *pTmp1 = aTmp;
-    char *pTmp2;
-    char *aTmp2;
-    int res = 1;
-
-    fts3PoslistPhraseMerge(&pTmp1, nRight, 0, 0, pp1, pp2);
-    aTmp2 = pTmp2 = pTmp1;
-    *pp1 = p1;
-    *pp2 = p2;
-    fts3PoslistPhraseMerge(&pTmp2, nLeft, 1, 0, pp2, pp1);
-    if( pTmp1!=aTmp && pTmp2!=aTmp2 ){
-      fts3PoslistMerge(pp, &aTmp, &aTmp2);
-    }else if( pTmp1!=aTmp ){
-      fts3PoslistCopy(pp, &aTmp);
-    }else if( pTmp2!=aTmp2 ){
-      fts3PoslistCopy(pp, &aTmp2);
+    sqlite3_int64 iVal;
+    *pp += sqlite3Fts3GetVarint(*pp, &iVal);
+    if( bDescIdx ){
+      *pVal -= iVal;
     }else{
-      res = 0;
+      *pVal += iVal;
     }
+  }
+}
 
-    return res;
+/*
+** This function is used to write a single varint to a buffer. The varint
+** is written to *pp. Before returning, *pp is set to point 1 byte past the
+** end of the value written.
+**
+** If *pbFirst is zero when this function is called, the value written to
+** the buffer is that of parameter iVal. 
+**
+** If *pbFirst is non-zero when this function is called, then the value 
+** written is either (iVal-*piPrev) (if bDescIdx is zero) or (*piPrev-iVal)
+** (if bDescIdx is non-zero).
+**
+** Before returning, this function always sets *pbFirst to 1 and *piPrev
+** to the value of parameter iVal.
+*/
+static void fts3PutDeltaVarint3(
+  char **pp,                      /* IN/OUT: Output pointer */
+  int bDescIdx,                   /* True for descending docids */
+  sqlite3_int64 *piPrev,          /* IN/OUT: Previous value written to list */
+  int *pbFirst,                   /* IN/OUT: True after first int written */
+  sqlite3_int64 iVal              /* Write this value to the list */
+){
+  sqlite3_int64 iWrite;
+  if( bDescIdx==0 || *pbFirst==0 ){
+    iWrite = iVal - *piPrev;
+  }else{
+    iWrite = *piPrev - iVal;
   }
+  assert( *pbFirst || *piPrev==0 );
+  assert( *pbFirst==0 || iWrite>0 );
+  *pp += sqlite3Fts3PutVarint(*pp, iWrite);
+  *piPrev = iVal;
+  *pbFirst = 1;
 }
 
+
 /*
-** Values that may be used as the first parameter to fts3DoclistMerge().
+** This macro is used by various functions that merge doclists. The two
+** arguments are 64-bit docid values. If the value of the stack variable
+** bDescDoclist is 0 when this macro is invoked, then it returns (i1-i2). 
+** Otherwise, (i2-i1).
+**
+** Using this makes it easier to write code that can merge doclists that are
+** sorted in either ascending or descending order.
 */
-#define MERGE_NOT        2        /* D + D -> D */
-#define MERGE_AND        3        /* D + D -> D */
-#define MERGE_OR         4        /* D + D -> D */
-#define MERGE_POS_OR     5        /* P + P -> P */
-#define MERGE_PHRASE     6        /* P + P -> D */
-#define MERGE_POS_PHRASE 7        /* P + P -> P */
-#define MERGE_NEAR       8        /* P + P -> D */
-#define MERGE_POS_NEAR   9        /* P + P -> P */
+#define DOCID_CMP(i1, i2) ((bDescDoclist?-1:1) * (i1-i2))
 
 /*
-** Merge the two doclists passed in buffer a1 (size n1 bytes) and a2
-** (size n2 bytes). The output is written to pre-allocated buffer aBuffer,
-** which is guaranteed to be large enough to hold the results. The number
-** of bytes written to aBuffer is stored in *pnBuffer before returning.
+** This function does an "OR" merge of two doclists (output contains all
+** positions contained in either argument doclist). If the docids in the 
+** input doclists are sorted in ascending order, parameter bDescDoclist
+** should be false. If they are sorted in ascending order, it should be
+** passed a non-zero value.
+**
+** If no error occurs, *paOut is set to point at an sqlite3_malloc'd buffer
+** containing the output doclist and SQLITE_OK is returned. In this case
+** *pnOut is set to the number of bytes in the output doclist.
 **
-** If successful, SQLITE_OK is returned. Otherwise, if a malloc error
-** occurs while allocating a temporary buffer as part of the merge operation,
-** SQLITE_NOMEM is returned.
+** If an error occurs, an SQLite error code is returned. The output values
+** are undefined in this case.
 */
-static int fts3DoclistMerge(
-  int mergetype,                  /* One of the MERGE_XXX constants */
-  int nParam1,                    /* Used by MERGE_NEAR and MERGE_POS_NEAR */
-  int nParam2,                    /* Used by MERGE_NEAR and MERGE_POS_NEAR */
-  char *aBuffer,                  /* Pre-allocated output buffer */
-  int *pnBuffer,                  /* OUT: Bytes written to aBuffer */
-  char *a1,                       /* Buffer containing first doclist */
-  int n1,                         /* Size of buffer a1 */
-  char *a2,                       /* Buffer containing second doclist */
-  int n2,                         /* Size of buffer a2 */
-  int *pnDoc                      /* OUT: Number of docids in output */
+static int fts3DoclistOrMerge(
+  int bDescDoclist,               /* True if arguments are desc */
+  char *a1, int n1,               /* First doclist */
+  char *a2, int n2,               /* Second doclist */
+  char **paOut, int *pnOut        /* OUT: Malloc'd doclist */
 ){
   sqlite3_int64 i1 = 0;
   sqlite3_int64 i2 = 0;
   sqlite3_int64 iPrev = 0;
-
-  char *p = aBuffer;
-  char *p1 = a1;
-  char *p2 = a2;
   char *pEnd1 = &a1[n1];
   char *pEnd2 = &a2[n2];
-  int nDoc = 0;
+  char *p1 = a1;
+  char *p2 = a2;
+  char *p;
+  char *aOut;
+  int bFirstOut = 0;
 
-  assert( mergetype==MERGE_OR     || mergetype==MERGE_POS_OR 
-       || mergetype==MERGE_AND    || mergetype==MERGE_NOT
-       || mergetype==MERGE_PHRASE || mergetype==MERGE_POS_PHRASE
-       || mergetype==MERGE_NEAR   || mergetype==MERGE_POS_NEAR
-  );
+  *paOut = 0;
+  *pnOut = 0;
 
-  if( !aBuffer ){
-    *pnBuffer = 0;
-    return SQLITE_NOMEM;
+  /* Allocate space for the output. Both the input and output doclists
+  ** are delta encoded. If they are in ascending order (bDescDoclist==0),
+  ** then the first docid in each list is simply encoded as a varint. For
+  ** each subsequent docid, the varint stored is the difference between the
+  ** current and previous docid (a positive number - since the list is in
+  ** ascending order).
+  **
+  ** The first docid written to the output is therefore encoded using the 
+  ** same number of bytes as it is in whichever of the input lists it is
+  ** read from. And each subsequent docid read from the same input list 
+  ** consumes either the same or less bytes as it did in the input (since
+  ** the difference between it and the previous value in the output must
+  ** be a positive value less than or equal to the delta value read from 
+  ** the input list). The same argument applies to all but the first docid
+  ** read from the 'other' list. And to the contents of all position lists
+  ** that will be copied and merged from the input to the output.
+  **
+  ** However, if the first docid copied to the output is a negative number,
+  ** then the encoding of the first docid from the 'other' input list may
+  ** be larger in the output than it was in the input (since the delta value
+  ** may be a larger positive integer than the actual docid).
+  **
+  ** The space required to store the output is therefore the sum of the
+  ** sizes of the two inputs, plus enough space for exactly one of the input
+  ** docids to grow. 
+  **
+  ** A symetric argument may be made if the doclists are in descending 
+  ** order.
+  */
+  aOut = sqlite3_malloc(n1+n2+FTS3_VARINT_MAX-1);
+  if( !aOut ) return SQLITE_NOMEM;
+
+  p = aOut;
+  fts3GetDeltaVarint3(&p1, pEnd1, 0, &i1);
+  fts3GetDeltaVarint3(&p2, pEnd2, 0, &i2);
+  while( p1 || p2 ){
+    sqlite3_int64 iDiff = DOCID_CMP(i1, i2);
+
+    if( p2 && p1 && iDiff==0 ){
+      fts3PutDeltaVarint3(&p, bDescDoclist, &iPrev, &bFirstOut, i1);
+      fts3PoslistMerge(&p, &p1, &p2);
+      fts3GetDeltaVarint3(&p1, pEnd1, bDescDoclist, &i1);
+      fts3GetDeltaVarint3(&p2, pEnd2, bDescDoclist, &i2);
+    }else if( !p2 || (p1 && iDiff<0) ){
+      fts3PutDeltaVarint3(&p, bDescDoclist, &iPrev, &bFirstOut, i1);
+      fts3PoslistCopy(&p, &p1);
+      fts3GetDeltaVarint3(&p1, pEnd1, bDescDoclist, &i1);
+    }else{
+      fts3PutDeltaVarint3(&p, bDescDoclist, &iPrev, &bFirstOut, i2);
+      fts3PoslistCopy(&p, &p2);
+      fts3GetDeltaVarint3(&p2, pEnd2, bDescDoclist, &i2);
+    }
   }
 
-  /* Read the first docid from each doclist */
-  fts3GetDeltaVarint2(&p1, pEnd1, &i1);
-  fts3GetDeltaVarint2(&p2, pEnd2, &i2);
-
-  switch( mergetype ){
-    case MERGE_OR:
-    case MERGE_POS_OR:
-      while( p1 || p2 ){
-        if( p2 && p1 && i1==i2 ){
-          fts3PutDeltaVarint(&p, &iPrev, i1);
-          if( mergetype==MERGE_POS_OR ) fts3PoslistMerge(&p, &p1, &p2);
-          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
-          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
-        }else if( !p2 || (p1 && i1<i2) ){
-          fts3PutDeltaVarint(&p, &iPrev, i1);
-          if( mergetype==MERGE_POS_OR ) fts3PoslistCopy(&p, &p1);
-          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
-        }else{
-          fts3PutDeltaVarint(&p, &iPrev, i2);
-          if( mergetype==MERGE_POS_OR ) fts3PoslistCopy(&p, &p2);
-          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
-        }
-      }
-      break;
-
-    case MERGE_AND:
-      while( p1 && p2 ){
-        if( i1==i2 ){
-          fts3PutDeltaVarint(&p, &iPrev, i1);
-          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
-          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
-          nDoc++;
-        }else if( i1<i2 ){
-          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
-        }else{
-          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
-        }
-      }
-      break;
+  *paOut = aOut;
+  *pnOut = (int)(p-aOut);
+  assert( *pnOut<=n1+n2+FTS3_VARINT_MAX-1 );
+  return SQLITE_OK;
+}
 
-    case MERGE_NOT:
-      while( p1 ){
-        if( p2 && i1==i2 ){
-          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
-          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
-        }else if( !p2 || i1<i2 ){
-          fts3PutDeltaVarint(&p, &iPrev, i1);
-          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
-        }else{
-          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
-        }
-      }
-      break;
+/*
+** This function does a "phrase" merge of two doclists. In a phrase merge,
+** the output contains a copy of each position from the right-hand input
+** doclist for which there is a position in the left-hand input doclist
+** exactly nDist tokens before it.
+**
+** If the docids in the input doclists are sorted in ascending order,
+** parameter bDescDoclist should be false. If they are sorted in ascending 
+** order, it should be passed a non-zero value.
+**
+** The right-hand input doclist is overwritten by this function.
+*/
+static void fts3DoclistPhraseMerge(
+  int bDescDoclist,               /* True if arguments are desc */
+  int nDist,                      /* Distance from left to right (1=adjacent) */
+  char *aLeft, int nLeft,         /* Left doclist */
+  char *aRight, int *pnRight      /* IN/OUT: Right/output doclist */
+){
+  sqlite3_int64 i1 = 0;
+  sqlite3_int64 i2 = 0;
+  sqlite3_int64 iPrev = 0;
+  char *pEnd1 = &aLeft[nLeft];
+  char *pEnd2 = &aRight[*pnRight];
+  char *p1 = aLeft;
+  char *p2 = aRight;
+  char *p;
+  int bFirstOut = 0;
+  char *aOut = aRight;
+
+  assert( nDist>0 );
+
+  p = aOut;
+  fts3GetDeltaVarint3(&p1, pEnd1, 0, &i1);
+  fts3GetDeltaVarint3(&p2, pEnd2, 0, &i2);
+
+  while( p1 && p2 ){
+    sqlite3_int64 iDiff = DOCID_CMP(i1, i2);
+    if( iDiff==0 ){
+      char *pSave = p;
+      sqlite3_int64 iPrevSave = iPrev;
+      int bFirstOutSave = bFirstOut;
 
-    case MERGE_POS_PHRASE:
-    case MERGE_PHRASE: {
-      char **ppPos = (mergetype==MERGE_PHRASE ? 0 : &p);
-      while( p1 && p2 ){
-        if( i1==i2 ){
-          char *pSave = p;
-          sqlite3_int64 iPrevSave = iPrev;
-          fts3PutDeltaVarint(&p, &iPrev, i1);
-          if( 0==fts3PoslistPhraseMerge(ppPos, nParam1, 0, 1, &p1, &p2) ){
-            p = pSave;
-            iPrev = iPrevSave;
-          }else{
-            nDoc++;
-          }
-          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
-          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
-        }else if( i1<i2 ){
-          fts3PoslistCopy(0, &p1);
-          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
-        }else{
-          fts3PoslistCopy(0, &p2);
-          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
-        }
+      fts3PutDeltaVarint3(&p, bDescDoclist, &iPrev, &bFirstOut, i1);
+      if( 0==fts3PoslistPhraseMerge(&p, nDist, 0, 1, &p1, &p2) ){
+        p = pSave;
+        iPrev = iPrevSave;
+        bFirstOut = bFirstOutSave;
       }
-      break;
+      fts3GetDeltaVarint3(&p1, pEnd1, bDescDoclist, &i1);
+      fts3GetDeltaVarint3(&p2, pEnd2, bDescDoclist, &i2);
+    }else if( iDiff<0 ){
+      fts3PoslistCopy(0, &p1);
+      fts3GetDeltaVarint3(&p1, pEnd1, bDescDoclist, &i1);
+    }else{
+      fts3PoslistCopy(0, &p2);
+      fts3GetDeltaVarint3(&p2, pEnd2, bDescDoclist, &i2);
     }
+  }
 
-    default: assert( mergetype==MERGE_POS_NEAR || mergetype==MERGE_NEAR ); {
-      char *aTmp = 0;
-      char **ppPos = 0;
-
-      if( mergetype==MERGE_POS_NEAR ){
-        ppPos = &p;
-        aTmp = sqlite3_malloc(2*(n1+n2+1));
-        if( !aTmp ){
-          return SQLITE_NOMEM;
-        }
-      }
-
-      while( p1 && p2 ){
-        if( i1==i2 ){
-          char *pSave = p;
-          sqlite3_int64 iPrevSave = iPrev;
-          fts3PutDeltaVarint(&p, &iPrev, i1);
+  *pnRight = (int)(p - aOut);
+}
 
-          if( !fts3PoslistNearMerge(ppPos, aTmp, nParam1, nParam2, &p1, &p2) ){
-            iPrev = iPrevSave;
-            p = pSave;
-          }
+/*
+** Argument pList points to a position list nList bytes in size. This
+** function checks to see if the position list contains any entries for
+** a token in position 0 (of any column). If so, it writes argument iDelta
+** to the output buffer pOut, followed by a position list consisting only
+** of the entries from pList at position 0, and terminated by an 0x00 byte.
+** The value returned is the number of bytes written to pOut (if any).
+*/
+int sqlite3Fts3FirstFilter(
+  sqlite3_int64 iDelta,           /* Varint that may be written to pOut */
+  char *pList,                    /* Position list (no 0x00 term) */
+  int nList,                      /* Size of pList in bytes */
+  char *pOut                      /* Write output here */
+){
+  int nOut = 0;
+  int bWritten = 0;               /* True once iDelta has been written */
+  char *p = pList;
+  char *pEnd = &pList[nList];
+
+  if( *p!=0x01 ){
+    if( *p==0x02 ){
+      nOut += sqlite3Fts3PutVarint(&pOut[nOut], iDelta);
+      pOut[nOut++] = 0x02;
+      bWritten = 1;
+    }
+    fts3ColumnlistCopy(0, &p);
+  }
 
-          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
-          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
-        }else if( i1<i2 ){
-          fts3PoslistCopy(0, &p1);
-          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
-        }else{
-          fts3PoslistCopy(0, &p2);
-          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
-        }
+  while( p<pEnd && *p==0x01 ){
+    sqlite3_int64 iCol;
+    p++;
+    p += sqlite3Fts3GetVarint(p, &iCol);
+    if( *p==0x02 ){
+      if( bWritten==0 ){
+        nOut += sqlite3Fts3PutVarint(&pOut[nOut], iDelta);
+        bWritten = 1;
       }
-      sqlite3_free(aTmp);
-      break;
+      pOut[nOut++] = 0x01;
+      nOut += sqlite3Fts3PutVarint(&pOut[nOut], iCol);
+      pOut[nOut++] = 0x02;
     }
+    fts3ColumnlistCopy(0, &p);
+  }
+  if( bWritten ){
+    pOut[nOut++] = 0x00;
   }
 
-  if( pnDoc ) *pnDoc = nDoc;
-  *pnBuffer = (int)(p-aBuffer);
-  return SQLITE_OK;
+  return nOut;
 }
 
-/* 
-** A pointer to an instance of this structure is used as the context 
-** argument to sqlite3Fts3SegReaderIterate()
-*/
-typedef struct TermSelect TermSelect;
-struct TermSelect {
-  int isReqPos;
-  char *aaOutput[16];             /* Malloc'd output buffer */
-  int anOutput[16];               /* Size of output in bytes */
-};
 
 /*
 ** Merge all doclists in the TermSelect.aaOutput[] array into a single
@@ -1949,8 +2602,7 @@ struct TermSelect {
 ** the responsibility of the caller to free any doclists left in the
 ** TermSelect.aaOutput[] array.
 */
-static int fts3TermSelectMerge(TermSelect *pTS){
-  int mergetype = (pTS->isReqPos ? MERGE_POS_OR : MERGE_OR);
+static int fts3TermSelectFinishMerge(Fts3Table *p, TermSelect *pTS){
   char *aOut = 0;
   int nOut = 0;
   int i;
@@ -1965,15 +2617,17 @@ static int fts3TermSelectMerge(TermSelect *pTS){
         nOut = pTS->anOutput[i];
         pTS->aaOutput[i] = 0;
       }else{
-        int nNew = nOut + pTS->anOutput[i];
-        char *aNew = sqlite3_malloc(nNew);
-        if( !aNew ){
+        int nNew;
+        char *aNew;
+
+        int rc = fts3DoclistOrMerge(p->bDescIdx, 
+            pTS->aaOutput[i], pTS->anOutput[i], aOut, nOut, &aNew, &nNew
+        );
+        if( rc!=SQLITE_OK ){
           sqlite3_free(aOut);
-          return SQLITE_NOMEM;
+          return rc;
         }
-        fts3DoclistMerge(mergetype, 0, 0,
-            aNew, &nNew, pTS->aaOutput[i], pTS->anOutput[i], aOut, nOut, 0
-        );
+
         sqlite3_free(pTS->aaOutput[i]);
         sqlite3_free(aOut);
         pTS->aaOutput[i] = 0;
@@ -1989,29 +2643,28 @@ static int fts3TermSelectMerge(TermSelect *pTS){
 }
 
 /*
-** This function is used as the sqlite3Fts3SegReaderIterate() callback when
-** querying the full-text index for a doclist associated with a term or
-** term-prefix.
+** Merge the doclist aDoclist/nDoclist into the TermSelect object passed
+** as the first argument. The merge is an "OR" merge (see function
+** fts3DoclistOrMerge() for details).
+**
+** This function is called with the doclist for each term that matches
+** a queried prefix. It merges all these doclists into one, the doclist
+** for the specified prefix. Since there can be a very large number of
+** doclists to merge, the merging is done pair-wise using the TermSelect
+** object.
+**
+** This function returns SQLITE_OK if the merge is successful, or an
+** SQLite error code (SQLITE_NOMEM) if an error occurs.
 */
-static int fts3TermSelectCb(
-  Fts3Table *p,                   /* Virtual table object */
-  void *pContext,                 /* Pointer to TermSelect structure */
-  char *zTerm,
-  int nTerm,
-  char *aDoclist,
-  int nDoclist
+static int fts3TermSelectMerge(
+  Fts3Table *p,                   /* FTS table handle */
+  TermSelect *pTS,                /* TermSelect object to merge into */
+  char *aDoclist,                 /* Pointer to doclist */
+  int nDoclist                    /* Size of aDoclist in bytes */
 ){
-  TermSelect *pTS = (TermSelect *)pContext;
-
-  UNUSED_PARAMETER(p);
-  UNUSED_PARAMETER(zTerm);
-  UNUSED_PARAMETER(nTerm);
-
   if( pTS->aaOutput[0]==0 ){
     /* If this is the first term selected, copy the doclist to the output
-    ** buffer using memcpy(). TODO: Add a way to transfer control of the
-    ** aDoclist buffer from the caller so as to avoid the memcpy().
-    */
+    ** buffer using memcpy(). */
     pTS->aaOutput[0] = sqlite3_malloc(nDoclist);
     pTS->anOutput[0] = nDoclist;
     if( pTS->aaOutput[0] ){
@@ -2020,126 +2673,108 @@ static int fts3TermSelectCb(
       return SQLITE_NOMEM;
     }
   }else{
-    int mergetype = (pTS->isReqPos ? MERGE_POS_OR : MERGE_OR);
     char *aMerge = aDoclist;
     int nMerge = nDoclist;
     int iOut;
 
     for(iOut=0; iOut<SizeofArray(pTS->aaOutput); iOut++){
-      char *aNew;
-      int nNew;
       if( pTS->aaOutput[iOut]==0 ){
         assert( iOut>0 );
         pTS->aaOutput[iOut] = aMerge;
         pTS->anOutput[iOut] = nMerge;
         break;
-      }
+      }else{
+        char *aNew;
+        int nNew;
 
-      nNew = nMerge + pTS->anOutput[iOut];
-      aNew = sqlite3_malloc(nNew);
-      if( !aNew ){
-        if( aMerge!=aDoclist ){
-          sqlite3_free(aMerge);
+        int rc = fts3DoclistOrMerge(p->bDescIdx, aMerge, nMerge, 
+            pTS->aaOutput[iOut], pTS->anOutput[iOut], &aNew, &nNew
+        );
+        if( rc!=SQLITE_OK ){
+          if( aMerge!=aDoclist ) sqlite3_free(aMerge);
+          return rc;
         }
-        return SQLITE_NOMEM;
-      }
-      fts3DoclistMerge(mergetype, 0, 0, aNew, &nNew, 
-          pTS->aaOutput[iOut], pTS->anOutput[iOut], aMerge, nMerge, 0
-      );
-
-      if( iOut>0 ) sqlite3_free(aMerge);
-      sqlite3_free(pTS->aaOutput[iOut]);
-      pTS->aaOutput[iOut] = 0;
 
-      aMerge = aNew;
-      nMerge = nNew;
-      if( (iOut+1)==SizeofArray(pTS->aaOutput) ){
-        pTS->aaOutput[iOut] = aMerge;
-        pTS->anOutput[iOut] = nMerge;
+        if( aMerge!=aDoclist ) sqlite3_free(aMerge);
+        sqlite3_free(pTS->aaOutput[iOut]);
+        pTS->aaOutput[iOut] = 0;
+  
+        aMerge = aNew;
+        nMerge = nNew;
+        if( (iOut+1)==SizeofArray(pTS->aaOutput) ){
+          pTS->aaOutput[iOut] = aMerge;
+          pTS->anOutput[iOut] = nMerge;
+        }
       }
     }
   }
   return SQLITE_OK;
 }
 
-static int fts3DeferredTermSelect(
-  Fts3DeferredToken *pToken,      /* Phrase token */
-  int isTermPos,                  /* True to include positions */
-  int *pnOut,                     /* OUT: Size of list */
-  char **ppOut                    /* OUT: Body of list */
+/*
+** Append SegReader object pNew to the end of the pCsr->apSegment[] array.
+*/
+static int fts3SegReaderCursorAppend(
+  Fts3MultiSegReader *pCsr, 
+  Fts3SegReader *pNew
 ){
-  char *aSource;
-  int nSource;
-
-  aSource = sqlite3Fts3DeferredDoclist(pToken, &nSource);
-  if( !aSource ){
-    *pnOut = 0;
-    *ppOut = 0;
-  }else if( isTermPos ){
-    *ppOut = sqlite3_malloc(nSource);
-    if( !*ppOut ) return SQLITE_NOMEM;
-    memcpy(*ppOut, aSource, nSource);
-    *pnOut = nSource;
-  }else{
-    sqlite3_int64 docid;
-    *pnOut = sqlite3Fts3GetVarint(aSource, &docid);
-    *ppOut = sqlite3_malloc(*pnOut);
-    if( !*ppOut ) return SQLITE_NOMEM;
-    sqlite3Fts3PutVarint(*ppOut, docid);
+  if( (pCsr->nSegment%16)==0 ){
+    Fts3SegReader **apNew;
+    int nByte = (pCsr->nSegment + 16)*sizeof(Fts3SegReader*);
+    apNew = (Fts3SegReader **)sqlite3_realloc(pCsr->apSegment, nByte);
+    if( !apNew ){
+      sqlite3Fts3SegReaderFree(pNew);
+      return SQLITE_NOMEM;
+    }
+    pCsr->apSegment = apNew;
   }
-
+  pCsr->apSegment[pCsr->nSegment++] = pNew;
   return SQLITE_OK;
 }
 
-int sqlite3Fts3SegReaderCursor(
+/*
+** Add seg-reader objects to the Fts3MultiSegReader object passed as the
+** 8th argument.
+**
+** This function returns SQLITE_OK if successful, or an SQLite error code
+** otherwise.
+*/
+static int fts3SegReaderCursor(
   Fts3Table *p,                   /* FTS3 table handle */
+  int iLangid,                    /* Language id */
+  int iIndex,                     /* Index to search (from 0 to p->nIndex-1) */
   int iLevel,                     /* Level of segments to scan */
   const char *zTerm,              /* Term to query for */
   int nTerm,                      /* Size of zTerm in bytes */
   int isPrefix,                   /* True for a prefix search */
   int isScan,                     /* True to scan from zTerm to EOF */
-  Fts3SegReaderCursor *pCsr       /* Cursor object to populate */
+  Fts3MultiSegReader *pCsr        /* Cursor object to populate */
 ){
-  int rc = SQLITE_OK;
-  int rc2;
-  int iAge = 0;
-  sqlite3_stmt *pStmt = 0;
-  Fts3SegReader *pPending = 0;
-
-  assert( iLevel==FTS3_SEGCURSOR_ALL 
-      ||  iLevel==FTS3_SEGCURSOR_PENDING 
-      ||  iLevel>=0
-  );
-  assert( FTS3_SEGCURSOR_PENDING<0 );
-  assert( FTS3_SEGCURSOR_ALL<0 );
-  assert( iLevel==FTS3_SEGCURSOR_ALL || (zTerm==0 && isPrefix==1) );
-  assert( isPrefix==0 || isScan==0 );
-
-
-  memset(pCsr, 0, sizeof(Fts3SegReaderCursor));
-
-  /* If iLevel is less than 0, include a seg-reader for the pending-terms. */
-  assert( isScan==0 || fts3HashCount(&p->pendingTerms)==0 );
-  if( iLevel<0 && isScan==0 ){
-    rc = sqlite3Fts3SegReaderPending(p, zTerm, nTerm, isPrefix, &pPending);
-    if( rc==SQLITE_OK && pPending ){
-      int nByte = (sizeof(Fts3SegReader *) * 16);
-      pCsr->apSegment = (Fts3SegReader **)sqlite3_malloc(nByte);
-      if( pCsr->apSegment==0 ){
-        rc = SQLITE_NOMEM;
-      }else{
-        pCsr->apSegment[0] = pPending;
-        pCsr->nSegment = 1;
-        pPending = 0;
-      }
+  int rc = SQLITE_OK;             /* Error code */
+  sqlite3_stmt *pStmt = 0;        /* Statement to iterate through segments */
+  int rc2;                        /* Result of sqlite3_reset() */
+
+  /* If iLevel is less than 0 and this is not a scan, include a seg-reader 
+  ** for the pending-terms. If this is a scan, then this call must be being
+  ** made by an fts4aux module, not an FTS table. In this case calling
+  ** Fts3SegReaderPending might segfault, as the data structures used by 
+  ** fts4aux are not completely populated. So it's easiest to filter these
+  ** calls out here.  */
+  if( iLevel<0 && p->aIndex ){
+    Fts3SegReader *pSeg = 0;
+    rc = sqlite3Fts3SegReaderPending(p, iIndex, zTerm, nTerm, isPrefix, &pSeg);
+    if( rc==SQLITE_OK && pSeg ){
+      rc = fts3SegReaderCursorAppend(pCsr, pSeg);
     }
   }
 
   if( iLevel!=FTS3_SEGCURSOR_PENDING ){
     if( rc==SQLITE_OK ){
-      rc = sqlite3Fts3AllSegdirs(p, iLevel, &pStmt);
+      rc = sqlite3Fts3AllSegdirs(p, iLangid, iIndex, iLevel, &pStmt);
     }
+
     while( rc==SQLITE_OK && SQLITE_ROW==(rc = sqlite3_step(pStmt)) ){
+      Fts3SegReader *pSeg = 0;
 
       /* Read the values returned by the SELECT into local variables. */
       sqlite3_int64 iStartBlock = sqlite3_column_int64(pStmt, 1);
@@ -2148,18 +2783,6 @@ int sqlite3Fts3SegReaderCursor(
       int nRoot = sqlite3_column_bytes(pStmt, 4);
       char const *zRoot = sqlite3_column_blob(pStmt, 4);
 
-      /* If nSegment is a multiple of 16 the array needs to be extended. */
-      if( (pCsr->nSegment%16)==0 ){
-        Fts3SegReader **apNew;
-        int nByte = (pCsr->nSegment + 16)*sizeof(Fts3SegReader*);
-        apNew = (Fts3SegReader **)sqlite3_realloc(pCsr->apSegment, nByte);
-        if( !apNew ){
-          rc = SQLITE_NOMEM;
-          goto finished;
-        }
-        pCsr->apSegment = apNew;
-      }
-
       /* If zTerm is not NULL, and this segment is not stored entirely on its
       ** root node, the range of leaves scanned can be reduced. Do this. */
       if( iStartBlock && zTerm ){
@@ -2169,88 +2792,168 @@ int sqlite3Fts3SegReaderCursor(
         if( isPrefix==0 && isScan==0 ) iLeavesEndBlock = iStartBlock;
       }
  
-      rc = sqlite3Fts3SegReaderNew(iAge, iStartBlock, iLeavesEndBlock,
-          iEndBlock, zRoot, nRoot, &pCsr->apSegment[pCsr->nSegment]
+      rc = sqlite3Fts3SegReaderNew(pCsr->nSegment+1, 
+          (isPrefix==0 && isScan==0),
+          iStartBlock, iLeavesEndBlock, 
+          iEndBlock, zRoot, nRoot, &pSeg
       );
       if( rc!=SQLITE_OK ) goto finished;
-      pCsr->nSegment++;
-      iAge++;
+      rc = fts3SegReaderCursorAppend(pCsr, pSeg);
     }
   }
 
  finished:
   rc2 = sqlite3_reset(pStmt);
   if( rc==SQLITE_DONE ) rc = rc2;
-  sqlite3Fts3SegReaderFree(pPending);
 
   return rc;
 }
 
+/*
+** Set up a cursor object for iterating through a full-text index or a 
+** single level therein.
+*/
+int sqlite3Fts3SegReaderCursor(
+  Fts3Table *p,                   /* FTS3 table handle */
+  int iLangid,                    /* Language-id to search */
+  int iIndex,                     /* Index to search (from 0 to p->nIndex-1) */
+  int iLevel,                     /* Level of segments to scan */
+  const char *zTerm,              /* Term to query for */
+  int nTerm,                      /* Size of zTerm in bytes */
+  int isPrefix,                   /* True for a prefix search */
+  int isScan,                     /* True to scan from zTerm to EOF */
+  Fts3MultiSegReader *pCsr       /* Cursor object to populate */
+){
+  assert( iIndex>=0 && iIndex<p->nIndex );
+  assert( iLevel==FTS3_SEGCURSOR_ALL
+      ||  iLevel==FTS3_SEGCURSOR_PENDING 
+      ||  iLevel>=0
+  );
+  assert( iLevel<FTS3_SEGDIR_MAXLEVEL );
+  assert( FTS3_SEGCURSOR_ALL<0 && FTS3_SEGCURSOR_PENDING<0 );
+  assert( isPrefix==0 || isScan==0 );
+
+  memset(pCsr, 0, sizeof(Fts3MultiSegReader));
+  return fts3SegReaderCursor(
+      p, iLangid, iIndex, iLevel, zTerm, nTerm, isPrefix, isScan, pCsr
+  );
+}
+
+/*
+** In addition to its current configuration, have the Fts3MultiSegReader
+** passed as the 4th argument also scan the doclist for term zTerm/nTerm.
+**
+** SQLITE_OK is returned if no error occurs, otherwise an SQLite error code.
+*/
+static int fts3SegReaderCursorAddZero(
+  Fts3Table *p,                   /* FTS virtual table handle */
+  int iLangid,
+  const char *zTerm,              /* Term to scan doclist of */
+  int nTerm,                      /* Number of bytes in zTerm */
+  Fts3MultiSegReader *pCsr        /* Fts3MultiSegReader to modify */
+){
+  return fts3SegReaderCursor(p, 
+      iLangid, 0, FTS3_SEGCURSOR_ALL, zTerm, nTerm, 0, 0,pCsr
+  );
+}
 
+/*
+** Open an Fts3MultiSegReader to scan the doclist for term zTerm/nTerm. Or,
+** if isPrefix is true, to scan the doclist for all terms for which 
+** zTerm/nTerm is a prefix. If successful, return SQLITE_OK and write
+** a pointer to the new Fts3MultiSegReader to *ppSegcsr. Otherwise, return
+** an SQLite error code.
+**
+** It is the responsibility of the caller to free this object by eventually
+** passing it to fts3SegReaderCursorFree() 
+**
+** SQLITE_OK is returned if no error occurs, otherwise an SQLite error code.
+** Output parameter *ppSegcsr is set to 0 if an error occurs.
+*/
 static int fts3TermSegReaderCursor(
   Fts3Cursor *pCsr,               /* Virtual table cursor handle */
   const char *zTerm,              /* Term to query for */
   int nTerm,                      /* Size of zTerm in bytes */
   int isPrefix,                   /* True for a prefix search */
-  Fts3SegReaderCursor **ppSegcsr  /* OUT: Allocated seg-reader cursor */
+  Fts3MultiSegReader **ppSegcsr   /* OUT: Allocated seg-reader cursor */
 ){
-  Fts3SegReaderCursor *pSegcsr;   /* Object to allocate and return */
+  Fts3MultiSegReader *pSegcsr;    /* Object to allocate and return */
   int rc = SQLITE_NOMEM;          /* Return code */
 
-  pSegcsr = sqlite3_malloc(sizeof(Fts3SegReaderCursor));
+  pSegcsr = sqlite3_malloc(sizeof(Fts3MultiSegReader));
   if( pSegcsr ){
-    Fts3Table *p = (Fts3Table *)pCsr->base.pVtab;
     int i;
-    int nCost = 0;
-    rc = sqlite3Fts3SegReaderCursor(
-        p, FTS3_SEGCURSOR_ALL, zTerm, nTerm, isPrefix, 0, pSegcsr);
-  
-    for(i=0; rc==SQLITE_OK && i<pSegcsr->nSegment; i++){
-      rc = sqlite3Fts3SegReaderCost(pCsr, pSegcsr->apSegment[i], &nCost);
+    int bFound = 0;               /* True once an index has been found */
+    Fts3Table *p = (Fts3Table *)pCsr->base.pVtab;
+
+    if( isPrefix ){
+      for(i=1; bFound==0 && i<p->nIndex; i++){
+        if( p->aIndex[i].nPrefix==nTerm ){
+          bFound = 1;
+          rc = sqlite3Fts3SegReaderCursor(p, pCsr->iLangid, 
+              i, FTS3_SEGCURSOR_ALL, zTerm, nTerm, 0, 0, pSegcsr
+          );
+          pSegcsr->bLookup = 1;
+        }
+      }
+
+      for(i=1; bFound==0 && i<p->nIndex; i++){
+        if( p->aIndex[i].nPrefix==nTerm+1 ){
+          bFound = 1;
+          rc = sqlite3Fts3SegReaderCursor(p, pCsr->iLangid, 
+              i, FTS3_SEGCURSOR_ALL, zTerm, nTerm, 1, 0, pSegcsr
+          );
+          if( rc==SQLITE_OK ){
+            rc = fts3SegReaderCursorAddZero(
+                p, pCsr->iLangid, zTerm, nTerm, pSegcsr
+            );
+          }
+        }
+      }
+    }
+
+    if( bFound==0 ){
+      rc = sqlite3Fts3SegReaderCursor(p, pCsr->iLangid, 
+          0, FTS3_SEGCURSOR_ALL, zTerm, nTerm, isPrefix, 0, pSegcsr
+      );
+      pSegcsr->bLookup = !isPrefix;
     }
-    pSegcsr->nCost = nCost;
   }
 
   *ppSegcsr = pSegcsr;
   return rc;
 }
 
-static void fts3SegReaderCursorFree(Fts3SegReaderCursor *pSegcsr){
+/*
+** Free an Fts3MultiSegReader allocated by fts3TermSegReaderCursor().
+*/
+static void fts3SegReaderCursorFree(Fts3MultiSegReader *pSegcsr){
   sqlite3Fts3SegReaderFinish(pSegcsr);
   sqlite3_free(pSegcsr);
 }
 
 /*
-** This function retreives the doclist for the specified term (or term
-** prefix) from the database. 
-**
-** The returned doclist may be in one of two formats, depending on the 
-** value of parameter isReqPos. If isReqPos is zero, then the doclist is
-** a sorted list of delta-compressed docids (a bare doclist). If isReqPos
-** is non-zero, then the returned list is in the same format as is stored 
-** in the database without the found length specifier at the start of on-disk
-** doclists.
+** This function retrieves the doclist for the specified term (or term
+** prefix) from the database.
 */
 static int fts3TermSelect(
   Fts3Table *p,                   /* Virtual table handle */
   Fts3PhraseToken *pTok,          /* Token to query for */
   int iColumn,                    /* Column to query (or -ve for all columns) */
-  int isReqPos,                   /* True to include position lists in output */
   int *pnOut,                     /* OUT: Size of buffer at *ppOut */
   char **ppOut                    /* OUT: Malloced result buffer */
 ){
   int rc;                         /* Return code */
-  Fts3SegReaderCursor *pSegcsr;   /* Seg-reader cursor for this term */
-  TermSelect tsc;                 /* Context object for fts3TermSelectCb() */
+  Fts3MultiSegReader *pSegcsr;    /* Seg-reader cursor for this term */
+  TermSelect tsc;                 /* Object for pair-wise doclist merging */
   Fts3SegFilter filter;           /* Segment term filter configuration */
 
   pSegcsr = pTok->pSegcsr;
   memset(&tsc, 0, sizeof(TermSelect));
-  tsc.isReqPos = isReqPos;
 
-  filter.flags = FTS3_SEGMENT_IGNORE_EMPTY 
+  filter.flags = FTS3_SEGMENT_IGNORE_EMPTY | FTS3_SEGMENT_REQUIRE_POS
         | (pTok->isPrefix ? FTS3_SEGMENT_PREFIX : 0)
-        | (isReqPos ? FTS3_SEGMENT_REQUIRE_POS : 0)
+        | (pTok->bFirst ? FTS3_SEGMENT_FIRST : 0)
         | (iColumn<p->nColumn ? FTS3_SEGMENT_COLUMN_FILTER : 0);
   filter.iCol = iColumn;
   filter.zTerm = pTok->z;
@@ -2260,13 +2963,11 @@ static int fts3TermSelect(
   while( SQLITE_OK==rc
       && SQLITE_ROW==(rc = sqlite3Fts3SegReaderStep(p, pSegcsr)) 
   ){
-    rc = fts3TermSelectCb(p, (void *)&tsc, 
-        pSegcsr->zTerm, pSegcsr->nTerm, pSegcsr->aDoclist, pSegcsr->nDoclist
-    );
+    rc = fts3TermSelectMerge(p, &tsc, pSegcsr->aDoclist, pSegcsr->nDoclist);
   }
 
   if( rc==SQLITE_OK ){
-    rc = fts3TermSelectMerge(&tsc);
+    rc = fts3TermSelectFinishMerge(p, &tsc);
   }
   if( rc==SQLITE_OK ){
     *ppOut = tsc.aaOutput[0];
@@ -2292,24 +2993,15 @@ static int fts3TermSelect(
 ** that the doclist is simply a list of docids stored as delta encoded 
 ** varints.
 */
-static int fts3DoclistCountDocids(int isPoslist, char *aList, int nList){
+static int fts3DoclistCountDocids(char *aList, int nList){
   int nDoc = 0;                   /* Return value */
   if( aList ){
     char *aEnd = &aList[nList];   /* Pointer to one byte after EOF */
     char *p = aList;              /* Cursor */
-    if( !isPoslist ){
-      /* The number of docids in the list is the same as the number of 
-      ** varints. In FTS3 a varint consists of a single byte with the 0x80 
-      ** bit cleared and zero or more bytes with the 0x80 bit set. So to
-      ** count the varints in the buffer, just count the number of bytes
-      ** with the 0x80 bit clear.  */
-      while( p<aEnd ) nDoc += (((*p++)&0x80)==0);
-    }else{
-      while( p<aEnd ){
-        nDoc++;
-        while( (*p++)&0x80 );     /* Skip docid varint */
-        fts3PoslistCopy(0, &p);   /* Skip over position list */
-      }
+    while( p<aEnd ){
+      nDoc++;
+      while( (*p++)&0x80 );     /* Skip docid varint */
+      fts3PoslistCopy(0, &p);   /* Skip over position list */
     }
   }
 
@@ -2317,697 +3009,59 @@ static int fts3DoclistCountDocids(int isPoslist, char *aList, int nList){
 }
 
 /*
-** Call sqlite3Fts3DeferToken() for each token in the expression pExpr.
-*/
-static int fts3DeferExpression(Fts3Cursor *pCsr, Fts3Expr *pExpr){
-  int rc = SQLITE_OK;
-  if( pExpr ){
-    rc = fts3DeferExpression(pCsr, pExpr->pLeft);
-    if( rc==SQLITE_OK ){
-      rc = fts3DeferExpression(pCsr, pExpr->pRight);
-    }
-    if( pExpr->eType==FTSQUERY_PHRASE ){
-      int iCol = pExpr->pPhrase->iColumn;
-      int i;
-      for(i=0; rc==SQLITE_OK && i<pExpr->pPhrase->nToken; i++){
-        Fts3PhraseToken *pToken = &pExpr->pPhrase->aToken[i];
-        if( pToken->pDeferred==0 ){
-          rc = sqlite3Fts3DeferToken(pCsr, pToken, iCol);
-        }
-      }
-    }
-  }
-  return rc;
-}
-
-/*
-** This function removes the position information from a doclist. When
-** called, buffer aList (size *pnList bytes) contains a doclist that includes
-** position information. This function removes the position information so
-** that aList contains only docids, and adjusts *pnList to reflect the new
-** (possibly reduced) size of the doclist.
-*/
-static void fts3DoclistStripPositions(
-  char *aList,                    /* IN/OUT: Buffer containing doclist */
-  int *pnList                     /* IN/OUT: Size of doclist in bytes */
-){
-  if( aList ){
-    char *aEnd = &aList[*pnList]; /* Pointer to one byte after EOF */
-    char *p = aList;              /* Input cursor */
-    char *pOut = aList;           /* Output cursor */
-  
-    while( p<aEnd ){
-      sqlite3_int64 delta;
-      p += sqlite3Fts3GetVarint(p, &delta);
-      fts3PoslistCopy(0, &p);
-      pOut += sqlite3Fts3PutVarint(pOut, delta);
-    }
-
-    *pnList = (int)(pOut - aList);
-  }
-}
-
-/* 
-** Return a DocList corresponding to the phrase *pPhrase.
+** Advance the cursor to the next row in the %_content table that
+** matches the search criteria.  For a MATCH search, this will be
+** the next row that matches. For a full-table scan, this will be
+** simply the next row in the %_content table.  For a docid lookup,
+** this routine simply sets the EOF flag.
 **
-** If this function returns SQLITE_OK, but *pnOut is set to a negative value,
-** then no tokens in the phrase were looked up in the full-text index. This
-** is only possible when this function is called from within xFilter(). The
-** caller should assume that all documents match the phrase. The actual
-** filtering will take place in xNext().
+** Return SQLITE_OK if nothing goes wrong.  SQLITE_OK is returned
+** even if we reach end-of-file.  The fts3EofMethod() will be called
+** subsequently to determine whether or not an EOF was hit.
 */
-static int fts3PhraseSelect(
-  Fts3Cursor *pCsr,               /* Virtual table cursor handle */
-  Fts3Phrase *pPhrase,            /* Phrase to return a doclist for */
-  int isReqPos,                   /* True if output should contain positions */
-  char **paOut,                   /* OUT: Pointer to malloc'd result buffer */
-  int *pnOut                      /* OUT: Size of buffer at *paOut */
-){
-  char *pOut = 0;
-  int nOut = 0;
-  int rc = SQLITE_OK;
-  int ii;
-  int iCol = pPhrase->iColumn;
-  int isTermPos = (pPhrase->nToken>1 || isReqPos);
-  Fts3Table *p = (Fts3Table *)pCsr->base.pVtab;
-  int isFirst = 1;
-
-  int iPrevTok = 0;
-  int nDoc = 0;
-
-  /* If this is an xFilter() evaluation, create a segment-reader for each
-  ** phrase token. Or, if this is an xNext() or snippet/offsets/matchinfo
-  ** evaluation, only create segment-readers if there are no Fts3DeferredToken
-  ** objects attached to the phrase-tokens.
-  */
-  for(ii=0; ii<pPhrase->nToken; ii++){
-    Fts3PhraseToken *pTok = &pPhrase->aToken[ii];
-    if( pTok->pSegcsr==0 ){
-      if( (pCsr->eEvalmode==FTS3_EVAL_FILTER)
-       || (pCsr->eEvalmode==FTS3_EVAL_NEXT && pCsr->pDeferred==0) 
-       || (pCsr->eEvalmode==FTS3_EVAL_MATCHINFO && pTok->bFulltext) 
-      ){
-        rc = fts3TermSegReaderCursor(
-            pCsr, pTok->z, pTok->n, pTok->isPrefix, &pTok->pSegcsr
-        );
-        if( rc!=SQLITE_OK ) return rc;
-      }
-    }
-  }
-
-  for(ii=0; ii<pPhrase->nToken; ii++){
-    Fts3PhraseToken *pTok;        /* Token to find doclist for */
-    int iTok = 0;                 /* The token being queried this iteration */
-    char *pList = 0;              /* Pointer to token doclist */
-    int nList = 0;                /* Size of buffer at pList */
-
-    /* Select a token to process. If this is an xFilter() call, then tokens 
-    ** are processed in order from least to most costly. Otherwise, tokens 
-    ** are processed in the order in which they occur in the phrase.
-    */
-    if( pCsr->eEvalmode==FTS3_EVAL_MATCHINFO ){
-      assert( isReqPos );
-      iTok = ii;
-      pTok = &pPhrase->aToken[iTok];
-      if( pTok->bFulltext==0 ) continue;
-    }else if( pCsr->eEvalmode==FTS3_EVAL_NEXT || isReqPos ){
-      iTok = ii;
-      pTok = &pPhrase->aToken[iTok];
-    }else{
-      int nMinCost = 0x7FFFFFFF;
-      int jj;
-
-      /* Find the remaining token with the lowest cost. */
-      for(jj=0; jj<pPhrase->nToken; jj++){
-        Fts3SegReaderCursor *pSegcsr = pPhrase->aToken[jj].pSegcsr;
-        if( pSegcsr && pSegcsr->nCost<nMinCost ){
-          iTok = jj;
-          nMinCost = pSegcsr->nCost;
-        }
-      }
-      pTok = &pPhrase->aToken[iTok];
-
-      /* This branch is taken if it is determined that loading the doclist
-      ** for the next token would require more IO than loading all documents
-      ** currently identified by doclist pOut/nOut. No further doclists will
-      ** be loaded from the full-text index for this phrase.
-      */
-      if( nMinCost>nDoc && ii>0 ){
-        rc = fts3DeferExpression(pCsr, pCsr->pExpr);
-        break;
-      }
-    }
-
-    if( pCsr->eEvalmode==FTS3_EVAL_NEXT && pTok->pDeferred ){
-      rc = fts3DeferredTermSelect(pTok->pDeferred, isTermPos, &nList, &pList);
-    }else{
-      if( pTok->pSegcsr ){
-        rc = fts3TermSelect(p, pTok, iCol, isTermPos, &nList, &pList);
-      }
-      pTok->bFulltext = 1;
-    }
-    assert( rc!=SQLITE_OK || pCsr->eEvalmode || pTok->pSegcsr==0 );
-    if( rc!=SQLITE_OK ) break;
-
-    if( isFirst ){
-      pOut = pList;
-      nOut = nList;
-      if( pCsr->eEvalmode==FTS3_EVAL_FILTER && pPhrase->nToken>1 ){
-        nDoc = fts3DoclistCountDocids(1, pOut, nOut);
-      }
-      isFirst = 0;
-      iPrevTok = iTok;
+static int fts3NextMethod(sqlite3_vtab_cursor *pCursor){
+  int rc;
+  Fts3Cursor *pCsr = (Fts3Cursor *)pCursor;
+  if( pCsr->eSearch==FTS3_DOCID_SEARCH || pCsr->eSearch==FTS3_FULLSCAN_SEARCH ){
+    if( SQLITE_ROW!=sqlite3_step(pCsr->pStmt) ){
+      pCsr->isEof = 1;
+      rc = sqlite3_reset(pCsr->pStmt);
     }else{
-      /* Merge the new term list and the current output. */
-      char *aLeft, *aRight;
-      int nLeft, nRight;
-      int nDist;
-      int mt;
-
-      /* If this is the final token of the phrase, and positions were not
-      ** requested by the caller, use MERGE_PHRASE instead of POS_PHRASE.
-      ** This drops the position information from the output list.
-      */
-      mt = MERGE_POS_PHRASE;
-      if( ii==pPhrase->nToken-1 && !isReqPos ) mt = MERGE_PHRASE;
-
-      assert( iPrevTok!=iTok );
-      if( iPrevTok<iTok ){
-        aLeft = pOut;
-        nLeft = nOut;
-        aRight = pList;
-        nRight = nList;
-        nDist = iTok-iPrevTok;
-        iPrevTok = iTok;
-      }else{
-        aRight = pOut;
-        nRight = nOut;
-        aLeft = pList;
-        nLeft = nList;
-        nDist = iPrevTok-iTok;
-      }
-      pOut = aRight;
-      fts3DoclistMerge(
-          mt, nDist, 0, pOut, &nOut, aLeft, nLeft, aRight, nRight, &nDoc
-      );
-      sqlite3_free(aLeft);
-    }
-    assert( nOut==0 || pOut!=0 );
-  }
-
-  if( rc==SQLITE_OK ){
-    if( ii!=pPhrase->nToken ){
-      assert( pCsr->eEvalmode==FTS3_EVAL_FILTER && isReqPos==0 );
-      fts3DoclistStripPositions(pOut, &nOut);
+      pCsr->iPrevId = sqlite3_column_int64(pCsr->pStmt, 0);
+      rc = SQLITE_OK;
     }
-    *paOut = pOut;
-    *pnOut = nOut;
   }else{
-    sqlite3_free(pOut);
+    rc = fts3EvalNext((Fts3Cursor *)pCursor);
   }
+  assert( ((Fts3Table *)pCsr->base.pVtab)->pSegments==0 );
   return rc;
 }
 
 /*
-** This function merges two doclists according to the requirements of a
-** NEAR operator.
-**
-** Both input doclists must include position information. The output doclist 
-** includes position information if the first argument to this function
-** is MERGE_POS_NEAR, or does not if it is MERGE_NEAR.
-*/
-static int fts3NearMerge(
-  int mergetype,                  /* MERGE_POS_NEAR or MERGE_NEAR */
-  int nNear,                      /* Parameter to NEAR operator */
-  int nTokenLeft,                 /* Number of tokens in LHS phrase arg */
-  char *aLeft,                    /* Doclist for LHS (incl. positions) */
-  int nLeft,                      /* Size of LHS doclist in bytes */
-  int nTokenRight,                /* As nTokenLeft */
-  char *aRight,                   /* As aLeft */
-  int nRight,                     /* As nRight */
-  char **paOut,                   /* OUT: Results of merge (malloced) */
-  int *pnOut                      /* OUT: Sized of output buffer */
-){
-  char *aOut;                     /* Buffer to write output doclist to */
-  int rc;                         /* Return code */
-
-  assert( mergetype==MERGE_POS_NEAR || MERGE_NEAR );
-
-  aOut = sqlite3_malloc(nLeft+nRight+1);
-  if( aOut==0 ){
-    rc = SQLITE_NOMEM;
-  }else{
-    rc = fts3DoclistMerge(mergetype, nNear+nTokenRight, nNear+nTokenLeft, 
-      aOut, pnOut, aLeft, nLeft, aRight, nRight, 0
-    );
-    if( rc!=SQLITE_OK ){
-      sqlite3_free(aOut);
-      aOut = 0;
-    }
-  }
-
-  *paOut = aOut;
-  return rc;
-}
-
-/*
-** This function is used as part of the processing for the snippet() and
-** offsets() functions.
+** The following are copied from sqliteInt.h.
 **
-** Both pLeft and pRight are expression nodes of type FTSQUERY_PHRASE. Both
-** have their respective doclists (including position information) loaded
-** in Fts3Expr.aDoclist/nDoclist. This function removes all entries from
-** each doclist that are not within nNear tokens of a corresponding entry
-** in the other doclist.
-*/
-int sqlite3Fts3ExprNearTrim(Fts3Expr *pLeft, Fts3Expr *pRight, int nNear){
-  int rc;                         /* Return code */
-
-  assert( pLeft->eType==FTSQUERY_PHRASE );
-  assert( pRight->eType==FTSQUERY_PHRASE );
-  assert( pLeft->isLoaded && pRight->isLoaded );
-
-  if( pLeft->aDoclist==0 || pRight->aDoclist==0 ){
-    sqlite3_free(pLeft->aDoclist);
-    sqlite3_free(pRight->aDoclist);
-    pRight->aDoclist = 0;
-    pLeft->aDoclist = 0;
-    rc = SQLITE_OK;
-  }else{
-    char *aOut;                   /* Buffer in which to assemble new doclist */
-    int nOut;                     /* Size of buffer aOut in bytes */
-
-    rc = fts3NearMerge(MERGE_POS_NEAR, nNear, 
-        pLeft->pPhrase->nToken, pLeft->aDoclist, pLeft->nDoclist,
-        pRight->pPhrase->nToken, pRight->aDoclist, pRight->nDoclist,
-        &aOut, &nOut
-    );
-    if( rc!=SQLITE_OK ) return rc;
-    sqlite3_free(pRight->aDoclist);
-    pRight->aDoclist = aOut;
-    pRight->nDoclist = nOut;
-
-    rc = fts3NearMerge(MERGE_POS_NEAR, nNear, 
-        pRight->pPhrase->nToken, pRight->aDoclist, pRight->nDoclist,
-        pLeft->pPhrase->nToken, pLeft->aDoclist, pLeft->nDoclist,
-        &aOut, &nOut
-    );
-    sqlite3_free(pLeft->aDoclist);
-    pLeft->aDoclist = aOut;
-    pLeft->nDoclist = nOut;
-  }
-  return rc;
-}
-
-
-/*
-** Allocate an Fts3SegReaderArray for each token in the expression pExpr. 
-** The allocated objects are stored in the Fts3PhraseToken.pArray member
-** variables of each token structure.
-*/
-static int fts3ExprAllocateSegReaders(
-  Fts3Cursor *pCsr,               /* FTS3 table */
-  Fts3Expr *pExpr,                /* Expression to create seg-readers for */
-  int *pnExpr                     /* OUT: Number of AND'd expressions */
-){
-  int rc = SQLITE_OK;             /* Return code */
-
-  assert( pCsr->eEvalmode==FTS3_EVAL_FILTER );
-  if( pnExpr && pExpr->eType!=FTSQUERY_AND ){
-    (*pnExpr)++;
-    pnExpr = 0;
-  }
-
-  if( pExpr->eType==FTSQUERY_PHRASE ){
-    Fts3Phrase *pPhrase = pExpr->pPhrase;
-    int ii;
-
-    for(ii=0; rc==SQLITE_OK && ii<pPhrase->nToken; ii++){
-      Fts3PhraseToken *pTok = &pPhrase->aToken[ii];
-      if( pTok->pSegcsr==0 ){
-        rc = fts3TermSegReaderCursor(
-            pCsr, pTok->z, pTok->n, pTok->isPrefix, &pTok->pSegcsr
-        );
-      }
-    }
-  }else{ 
-    rc = fts3ExprAllocateSegReaders(pCsr, pExpr->pLeft, pnExpr);
-    if( rc==SQLITE_OK ){
-      rc = fts3ExprAllocateSegReaders(pCsr, pExpr->pRight, pnExpr);
-    }
-  }
-  return rc;
-}
-
-/*
-** Free the Fts3SegReaderArray objects associated with each token in the
-** expression pExpr. In other words, this function frees the resources
-** allocated by fts3ExprAllocateSegReaders().
+** Constants for the largest and smallest possible 64-bit signed integers.
+** These macros are designed to work correctly on both 32-bit and 64-bit
+** compilers.
 */
-static void fts3ExprFreeSegReaders(Fts3Expr *pExpr){
-  if( pExpr ){
-    Fts3Phrase *pPhrase = pExpr->pPhrase;
-    if( pPhrase ){
-      int kk;
-      for(kk=0; kk<pPhrase->nToken; kk++){
-        fts3SegReaderCursorFree(pPhrase->aToken[kk].pSegcsr);
-        pPhrase->aToken[kk].pSegcsr = 0;
-      }
-    }
-    fts3ExprFreeSegReaders(pExpr->pLeft);
-    fts3ExprFreeSegReaders(pExpr->pRight);
-  }
-}
-
-/*
-** Return the sum of the costs of all tokens in the expression pExpr. This
-** function must be called after Fts3SegReaderArrays have been allocated
-** for all tokens using fts3ExprAllocateSegReaders().
-*/
-static int fts3ExprCost(Fts3Expr *pExpr){
-  int nCost;                      /* Return value */
-  if( pExpr->eType==FTSQUERY_PHRASE ){
-    Fts3Phrase *pPhrase = pExpr->pPhrase;
-    int ii;
-    nCost = 0;
-    for(ii=0; ii<pPhrase->nToken; ii++){
-      Fts3SegReaderCursor *pSegcsr = pPhrase->aToken[ii].pSegcsr;
-      if( pSegcsr ) nCost += pSegcsr->nCost;
-    }
-  }else{
-    nCost = fts3ExprCost(pExpr->pLeft) + fts3ExprCost(pExpr->pRight);
-  }
-  return nCost;
-}
-
-/*
-** The following is a helper function (and type) for fts3EvalExpr(). It
-** must be called after Fts3SegReaders have been allocated for every token
-** in the expression. See the context it is called from in fts3EvalExpr()
-** for further explanation.
-*/
-typedef struct ExprAndCost ExprAndCost;
-struct ExprAndCost {
-  Fts3Expr *pExpr;
-  int nCost;
-};
-static void fts3ExprAssignCosts(
-  Fts3Expr *pExpr,                /* Expression to create seg-readers for */
-  ExprAndCost **ppExprCost        /* OUT: Write to *ppExprCost */
-){
-  if( pExpr->eType==FTSQUERY_AND ){
-    fts3ExprAssignCosts(pExpr->pLeft, ppExprCost);
-    fts3ExprAssignCosts(pExpr->pRight, ppExprCost);
-  }else{
-    (*ppExprCost)->pExpr = pExpr;
-    (*ppExprCost)->nCost = fts3ExprCost(pExpr);
-    (*ppExprCost)++;
-  }
-}
-
-/*
-** Evaluate the full-text expression pExpr against FTS3 table pTab. Store
-** the resulting doclist in *paOut and *pnOut. This routine mallocs for
-** the space needed to store the output. The caller is responsible for
-** freeing the space when it has finished.
-**
-** This function is called in two distinct contexts:
-**
-**   * From within the virtual table xFilter() method. In this case, the
-**     output doclist contains entries for all rows in the table, based on
-**     data read from the full-text index.
-**
-**     In this case, if the query expression contains one or more tokens that 
-**     are very common, then the returned doclist may contain a superset of 
-**     the documents that actually match the expression.
-**
-**   * From within the virtual table xNext() method. This call is only made
-**     if the call from within xFilter() found that there were very common 
-**     tokens in the query expression and did return a superset of the 
-**     matching documents. In this case the returned doclist contains only
-**     entries that correspond to the current row of the table. Instead of
-**     reading the data for each token from the full-text index, the data is
-**     already available in-memory in the Fts3PhraseToken.pDeferred structures.
-**     See fts3EvalDeferred() for how it gets there.
-**
-** In the first case above, Fts3Cursor.doDeferred==0. In the second (if it is
-** required) Fts3Cursor.doDeferred==1.
-**
-** If the SQLite invokes the snippet(), offsets() or matchinfo() function
-** as part of a SELECT on an FTS3 table, this function is called on each
-** individual phrase expression in the query. If there were very common tokens
-** found in the xFilter() call, then this function is called once for phrase
-** for each row visited, and the returned doclist contains entries for the
-** current row only. Otherwise, if there were no very common tokens, then this
-** function is called once only for each phrase in the query and the returned
-** doclist contains entries for all rows of the table.
-**
-** Fts3Cursor.doDeferred==1 when this function is called on phrases as a
-** result of a snippet(), offsets() or matchinfo() invocation.
-*/
-static int fts3EvalExpr(
-  Fts3Cursor *p,                  /* Virtual table cursor handle */
-  Fts3Expr *pExpr,                /* Parsed fts3 expression */
-  char **paOut,                   /* OUT: Pointer to malloc'd result buffer */
-  int *pnOut,                     /* OUT: Size of buffer at *paOut */
-  int isReqPos                    /* Require positions in output buffer */
-){
-  int rc = SQLITE_OK;             /* Return code */
-
-  /* Zero the output parameters. */
-  *paOut = 0;
-  *pnOut = 0;
-
-  if( pExpr ){
-    assert( pExpr->eType==FTSQUERY_NEAR   || pExpr->eType==FTSQUERY_OR     
-         || pExpr->eType==FTSQUERY_AND    || pExpr->eType==FTSQUERY_NOT
-         || pExpr->eType==FTSQUERY_PHRASE
-    );
-    assert( pExpr->eType==FTSQUERY_PHRASE || isReqPos==0 );
-
-    if( pExpr->eType==FTSQUERY_PHRASE ){
-      rc = fts3PhraseSelect(p, pExpr->pPhrase,
-          isReqPos || (pExpr->pParent && pExpr->pParent->eType==FTSQUERY_NEAR),
-          paOut, pnOut
-      );
-      fts3ExprFreeSegReaders(pExpr);
-    }else if( p->eEvalmode==FTS3_EVAL_FILTER && pExpr->eType==FTSQUERY_AND ){
-      ExprAndCost *aExpr = 0;     /* Array of AND'd expressions and costs */
-      int nExpr = 0;              /* Size of aExpr[] */
-      char *aRet = 0;             /* Doclist to return to caller */
-      int nRet = 0;               /* Length of aRet[] in bytes */
-      int nDoc = 0x7FFFFFFF;
-
-      assert( !isReqPos );
-
-      rc = fts3ExprAllocateSegReaders(p, pExpr, &nExpr);
-      if( rc==SQLITE_OK ){
-        assert( nExpr>1 );
-        aExpr = sqlite3_malloc(sizeof(ExprAndCost) * nExpr);
-        if( !aExpr ) rc = SQLITE_NOMEM;
-      }
-      if( rc==SQLITE_OK ){
-        int ii;                   /* Used to iterate through expressions */
-
-        fts3ExprAssignCosts(pExpr, &aExpr);
-        aExpr -= nExpr;
-        for(ii=0; ii<nExpr; ii++){
-          char *aNew;
-          int nNew;
-          int jj;
-          ExprAndCost *pBest = 0;
-  
-          for(jj=0; jj<nExpr; jj++){
-            ExprAndCost *pCand = &aExpr[jj];
-            if( pCand->pExpr && (pBest==0 || pCand->nCost<pBest->nCost) ){
-              pBest = pCand;
-            }
-          }
-  
-          if( pBest->nCost>nDoc ){
-            rc = fts3DeferExpression(p, p->pExpr);
-            break;
-          }else{
-            rc = fts3EvalExpr(p, pBest->pExpr, &aNew, &nNew, 0);
-            if( rc!=SQLITE_OK ) break;
-            pBest->pExpr = 0;
-            if( ii==0 ){
-              aRet = aNew;
-              nRet = nNew;
-              nDoc = fts3DoclistCountDocids(0, aRet, nRet);
-            }else{
-              fts3DoclistMerge(
-                  MERGE_AND, 0, 0, aRet, &nRet, aRet, nRet, aNew, nNew, &nDoc
-              );
-              sqlite3_free(aNew);
-            }
-          }
-        }
-      }
-
-      if( rc==SQLITE_OK ){
-        *paOut = aRet;
-        *pnOut = nRet;
-      }else{
-        assert( *paOut==0 );
-        sqlite3_free(aRet);
-      }
-      sqlite3_free(aExpr);
-      fts3ExprFreeSegReaders(pExpr);
-
-    }else{
-      char *aLeft;
-      char *aRight;
-      int nLeft;
-      int nRight;
-
-      assert( pExpr->eType==FTSQUERY_NEAR 
-           || pExpr->eType==FTSQUERY_OR
-           || pExpr->eType==FTSQUERY_NOT
-           || (pExpr->eType==FTSQUERY_AND && p->eEvalmode==FTS3_EVAL_NEXT)
-      );
-
-      if( 0==(rc = fts3EvalExpr(p, pExpr->pRight, &aRight, &nRight, isReqPos))
-       && 0==(rc = fts3EvalExpr(p, pExpr->pLeft, &aLeft, &nLeft, isReqPos))
-      ){
-        switch( pExpr->eType ){
-          case FTSQUERY_NEAR: {
-            Fts3Expr *pLeft;
-            Fts3Expr *pRight;
-            int mergetype = MERGE_NEAR;
-            if( pExpr->pParent && pExpr->pParent->eType==FTSQUERY_NEAR ){
-              mergetype = MERGE_POS_NEAR;
-            }
-            pLeft = pExpr->pLeft;
-            while( pLeft->eType==FTSQUERY_NEAR ){ 
-              pLeft=pLeft->pRight;
-            }
-            pRight = pExpr->pRight;
-            assert( pRight->eType==FTSQUERY_PHRASE );
-            assert( pLeft->eType==FTSQUERY_PHRASE );
-
-            rc = fts3NearMerge(mergetype, pExpr->nNear, 
-                pLeft->pPhrase->nToken, aLeft, nLeft,
-                pRight->pPhrase->nToken, aRight, nRight,
-                paOut, pnOut
-            );
-            sqlite3_free(aLeft);
-            break;
-          }
-
-          case FTSQUERY_OR: {
-            /* Allocate a buffer for the output. The maximum size is the
-            ** sum of the sizes of the two input buffers. The +1 term is
-            ** so that a buffer of zero bytes is never allocated - this can
-            ** cause fts3DoclistMerge() to incorrectly return SQLITE_NOMEM.
-            */
-            char *aBuffer = sqlite3_malloc(nRight+nLeft+1);
-            rc = fts3DoclistMerge(MERGE_OR, 0, 0, aBuffer, pnOut,
-                aLeft, nLeft, aRight, nRight, 0
-            );
-            *paOut = aBuffer;
-            sqlite3_free(aLeft);
-            break;
-          }
-
-          default: {
-            assert( FTSQUERY_NOT==MERGE_NOT && FTSQUERY_AND==MERGE_AND );
-            fts3DoclistMerge(pExpr->eType, 0, 0, aLeft, pnOut,
-                aLeft, nLeft, aRight, nRight, 0
-            );
-            *paOut = aLeft;
-            break;
-          }
-        }
-      }
-      sqlite3_free(aRight);
-    }
-  }
-
-  assert( rc==SQLITE_OK || *paOut==0 );
-  return rc;
-}
+#ifndef SQLITE_AMALGAMATION
+# define LARGEST_INT64  (0xffffffff|(((sqlite3_int64)0x7fffffff)<<32))
+# define SMALLEST_INT64 (((sqlite3_int64)-1) - LARGEST_INT64)
+#endif
 
 /*
-** This function is called from within xNext() for each row visited by
-** an FTS3 query. If evaluating the FTS3 query expression within xFilter()
-** was able to determine the exact set of matching rows, this function sets
-** *pbRes to true and returns SQLITE_IO immediately.
-**
-** Otherwise, if evaluating the query expression within xFilter() returned a
-** superset of the matching documents instead of an exact set (this happens
-** when the query includes very common tokens and it is deemed too expensive to
-** load their doclists from disk), this function tests if the current row
-** really does match the FTS3 query.
-**
-** If an error occurs, an SQLite error code is returned. Otherwise, SQLITE_OK
-** is returned and *pbRes is set to true if the current row matches the
-** FTS3 query (and should be included in the results returned to SQLite), or
-** false otherwise.
+** If the numeric type of argument pVal is "integer", then return it
+** converted to a 64-bit signed integer. Otherwise, return a copy of
+** the second parameter, iDefault.
 */
-static int fts3EvalDeferred(
-  Fts3Cursor *pCsr,               /* FTS3 cursor pointing at row to test */
-  int *pbRes                      /* OUT: Set to true if row is a match */
-){
-  int rc = SQLITE_OK;
-  if( pCsr->pDeferred==0 ){
-    *pbRes = 1;
-  }else{
-    rc = fts3CursorSeek(0, pCsr);
-    if( rc==SQLITE_OK ){
-      sqlite3Fts3FreeDeferredDoclists(pCsr);
-      rc = sqlite3Fts3CacheDeferredDoclists(pCsr);
-    }
-    if( rc==SQLITE_OK ){
-      char *a = 0;
-      int n = 0;
-      rc = fts3EvalExpr(pCsr, pCsr->pExpr, &a, &n, 0);
-      assert( n>=0 );
-      *pbRes = (n>0);
-      sqlite3_free(a);
+static sqlite3_int64 fts3DocidRange(sqlite3_value *pVal, i64 iDefault){
+  if( pVal ){
+    int eType = sqlite3_value_numeric_type(pVal);
+    if( eType==SQLITE_INTEGER ){
+      return sqlite3_value_int64(pVal);
     }
   }
-  return rc;
-}
-
-/*
-** Advance the cursor to the next row in the %_content table that
-** matches the search criteria.  For a MATCH search, this will be
-** the next row that matches. For a full-table scan, this will be
-** simply the next row in the %_content table.  For a docid lookup,
-** this routine simply sets the EOF flag.
-**
-** Return SQLITE_OK if nothing goes wrong.  SQLITE_OK is returned
-** even if we reach end-of-file.  The fts3EofMethod() will be called
-** subsequently to determine whether or not an EOF was hit.
-*/
-static int fts3NextMethod(sqlite3_vtab_cursor *pCursor){
-  int res;
-  int rc = SQLITE_OK;             /* Return code */
-  Fts3Cursor *pCsr = (Fts3Cursor *)pCursor;
-
-  pCsr->eEvalmode = FTS3_EVAL_NEXT;
-  do {
-    if( pCsr->aDoclist==0 ){
-      if( SQLITE_ROW!=sqlite3_step(pCsr->pStmt) ){
-        pCsr->isEof = 1;
-        rc = sqlite3_reset(pCsr->pStmt);
-        break;
-      }
-      pCsr->iPrevId = sqlite3_column_int64(pCsr->pStmt, 0);
-    }else{
-      if( pCsr->pNextId>=&pCsr->aDoclist[pCsr->nDoclist] ){
-        pCsr->isEof = 1;
-        break;
-      }
-      sqlite3_reset(pCsr->pStmt);
-      fts3GetDeltaVarint(&pCsr->pNextId, &pCsr->iPrevId);
-      pCsr->isRequireSeek = 1;
-      pCsr->isMatchinfoNeeded = 1;
-    }
-  }while( SQLITE_OK==(rc = fts3EvalDeferred(pCsr, &res)) && res==0 );
-
-  return rc;
+  return iDefault;
 }
 
 /*
@@ -3033,52 +3087,71 @@ static int fts3FilterMethod(
   int nVal,                       /* Number of elements in apVal */
   sqlite3_value **apVal           /* Arguments for the indexing scheme */
 ){
-  const char *azSql[] = {
-    "SELECT %s FROM %Q.'%q_content' AS x WHERE docid = ?", /* non-full-scan */
-    "SELECT %s FROM %Q.'%q_content' AS x ",                /* full-scan */
-  };
-  int rc;                         /* Return code */
+  int rc;
   char *zSql;                     /* SQL statement used to access %_content */
+  int eSearch;
   Fts3Table *p = (Fts3Table *)pCursor->pVtab;
   Fts3Cursor *pCsr = (Fts3Cursor *)pCursor;
 
+  sqlite3_value *pCons = 0;       /* The MATCH or rowid constraint, if any */
+  sqlite3_value *pLangid = 0;     /* The "langid = ?" constraint, if any */
+  sqlite3_value *pDocidGe = 0;    /* The "docid >= ?" constraint, if any */
+  sqlite3_value *pDocidLe = 0;    /* The "docid <= ?" constraint, if any */
+  int iIdx;
+
   UNUSED_PARAMETER(idxStr);
   UNUSED_PARAMETER(nVal);
 
-  assert( idxNum>=0 && idxNum<=(FTS3_FULLTEXT_SEARCH+p->nColumn) );
-  assert( nVal==0 || nVal==1 );
-  assert( (nVal==0)==(idxNum==FTS3_FULLSCAN_SEARCH) );
+  eSearch = (idxNum & 0x0000FFFF);
+  assert( eSearch>=0 && eSearch<=(FTS3_FULLTEXT_SEARCH+p->nColumn) );
   assert( p->pSegments==0 );
 
+  /* Collect arguments into local variables */
+  iIdx = 0;
+  if( eSearch!=FTS3_FULLSCAN_SEARCH ) pCons = apVal[iIdx++];
+  if( idxNum & FTS3_HAVE_LANGID ) pLangid = apVal[iIdx++];
+  if( idxNum & FTS3_HAVE_DOCID_GE ) pDocidGe = apVal[iIdx++];
+  if( idxNum & FTS3_HAVE_DOCID_LE ) pDocidLe = apVal[iIdx++];
+  assert( iIdx==nVal );
+
   /* In case the cursor has been used before, clear it now. */
   sqlite3_finalize(pCsr->pStmt);
   sqlite3_free(pCsr->aDoclist);
   sqlite3Fts3ExprFree(pCsr->pExpr);
   memset(&pCursor[1], 0, sizeof(Fts3Cursor)-sizeof(sqlite3_vtab_cursor));
 
-  if( idxNum!=FTS3_DOCID_SEARCH && idxNum!=FTS3_FULLSCAN_SEARCH ){
-    int iCol = idxNum-FTS3_FULLTEXT_SEARCH;
-    const char *zQuery = (const char *)sqlite3_value_text(apVal[0]);
+  /* Set the lower and upper bounds on docids to return */
+  pCsr->iMinDocid = fts3DocidRange(pDocidGe, SMALLEST_INT64);
+  pCsr->iMaxDocid = fts3DocidRange(pDocidLe, LARGEST_INT64);
+
+  if( idxStr ){
+    pCsr->bDesc = (idxStr[0]=='D');
+  }else{
+    pCsr->bDesc = p->bDescIdx;
+  }
+  pCsr->eSearch = (i16)eSearch;
+
+  if( eSearch!=FTS3_DOCID_SEARCH && eSearch!=FTS3_FULLSCAN_SEARCH ){
+    int iCol = eSearch-FTS3_FULLTEXT_SEARCH;
+    const char *zQuery = (const char *)sqlite3_value_text(pCons);
 
-    if( zQuery==0 && sqlite3_value_type(apVal[0])!=SQLITE_NULL ){
+    if( zQuery==0 && sqlite3_value_type(pCons)!=SQLITE_NULL ){
       return SQLITE_NOMEM;
     }
 
-    rc = sqlite3Fts3ExprParse(p->pTokenizer, p->azColumn, p->nColumn, 
-        iCol, zQuery, -1, &pCsr->pExpr
+    pCsr->iLangid = 0;
+    if( pLangid ) pCsr->iLangid = sqlite3_value_int(pLangid);
+
+    assert( p->base.zErrMsg==0 );
+    rc = sqlite3Fts3ExprParse(p->pTokenizer, pCsr->iLangid,
+        p->azColumn, p->bFts4, p->nColumn, iCol, zQuery, -1, &pCsr->pExpr, 
+        &p->base.zErrMsg
     );
     if( rc!=SQLITE_OK ){
-      if( rc==SQLITE_ERROR ){
-        p->base.zErrMsg = sqlite3_mprintf("malformed MATCH expression: [%s]",
-                                          zQuery);
-      }
       return rc;
     }
 
-    rc = sqlite3Fts3ReadLock(p);
-    if( rc!=SQLITE_OK ) return rc;
-
-    rc = fts3EvalExpr(pCsr, pCsr->pExpr, &pCsr->aDoclist, &pCsr->nDoclist, 0);
+    rc = fts3EvalStart(pCsr);
     sqlite3Fts3SegmentsClose(p);
     if( rc!=SQLITE_OK ) return rc;
     pCsr->pNextId = pCsr->aDoclist;
@@ -3090,20 +3163,25 @@ static int fts3FilterMethod(
   ** full-text query or docid lookup, the statement retrieves a single
   ** row by docid.
   */
-  zSql = (char *)azSql[idxNum==FTS3_FULLSCAN_SEARCH];
-  zSql = sqlite3_mprintf(zSql, p->zReadExprlist, p->zDb, p->zName);
-  if( !zSql ){
-    rc = SQLITE_NOMEM;
-  }else{
-    rc = sqlite3_prepare_v2(p->db, zSql, -1, &pCsr->pStmt, 0);
-    sqlite3_free(zSql);
-  }
-  if( rc==SQLITE_OK && idxNum==FTS3_DOCID_SEARCH ){
-    rc = sqlite3_bind_value(pCsr->pStmt, 1, apVal[0]);
+  if( eSearch==FTS3_FULLSCAN_SEARCH ){
+    zSql = sqlite3_mprintf(
+        "SELECT %s ORDER BY rowid %s",
+        p->zReadExprlist, (pCsr->bDesc ? "DESC" : "ASC")
+    );
+    if( zSql ){
+      rc = sqlite3_prepare_v2(p->db, zSql, -1, &pCsr->pStmt, 0);
+      sqlite3_free(zSql);
+    }else{
+      rc = SQLITE_NOMEM;
+    }
+  }else if( eSearch==FTS3_DOCID_SEARCH ){
+    rc = fts3CursorSeekStmt(pCsr, &pCsr->pStmt);
+    if( rc==SQLITE_OK ){
+      rc = sqlite3_bind_value(pCsr->pStmt, 1, pCons);
+    }
   }
-  pCsr->eSearch = (i16)idxNum;
-
   if( rc!=SQLITE_OK ) return rc;
+
   return fts3NextMethod(pCursor);
 }
 
@@ -3123,54 +3201,63 @@ static int fts3EofMethod(sqlite3_vtab_cursor *pCursor){
 */
 static int fts3RowidMethod(sqlite3_vtab_cursor *pCursor, sqlite_int64 *pRowid){
   Fts3Cursor *pCsr = (Fts3Cursor *) pCursor;
-  if( pCsr->aDoclist ){
-    *pRowid = pCsr->iPrevId;
-  }else{
-    /* This branch runs if the query is implemented using a full-table scan
-    ** (not using the full-text index). In this case grab the rowid from the
-    ** SELECT statement.
-    */
-    assert( pCsr->isRequireSeek==0 );
-    *pRowid = sqlite3_column_int64(pCsr->pStmt, 0);
-  }
+  *pRowid = pCsr->iPrevId;
   return SQLITE_OK;
 }
 
 /* 
 ** This is the xColumn method, called by SQLite to request a value from
 ** the row that the supplied cursor currently points to.
+**
+** If:
+**
+**   (iCol <  p->nColumn)   -> The value of the iCol'th user column.
+**   (iCol == p->nColumn)   -> Magic column with the same name as the table.
+**   (iCol == p->nColumn+1) -> Docid column
+**   (iCol == p->nColumn+2) -> Langid column
 */
 static int fts3ColumnMethod(
   sqlite3_vtab_cursor *pCursor,   /* Cursor to retrieve value from */
-  sqlite3_context *pContext,      /* Context for sqlite3_result_xxx() calls */
+  sqlite3_context *pCtx,          /* Context for sqlite3_result_xxx() calls */
   int iCol                        /* Index of column to read value from */
 ){
-  int rc;                         /* Return Code */
+  int rc = SQLITE_OK;             /* Return Code */
   Fts3Cursor *pCsr = (Fts3Cursor *) pCursor;
   Fts3Table *p = (Fts3Table *)pCursor->pVtab;
 
   /* The column value supplied by SQLite must be in range. */
-  assert( iCol>=0 && iCol<=p->nColumn+1 );
+  assert( iCol>=0 && iCol<=p->nColumn+2 );
 
   if( iCol==p->nColumn+1 ){
     /* This call is a request for the "docid" column. Since "docid" is an 
     ** alias for "rowid", use the xRowid() method to obtain the value.
     */
-    sqlite3_int64 iRowid;
-    rc = fts3RowidMethod(pCursor, &iRowid);
-    sqlite3_result_int64(pContext, iRowid);
+    sqlite3_result_int64(pCtx, pCsr->iPrevId);
   }else if( iCol==p->nColumn ){
     /* The extra column whose name is the same as the table.
-    ** Return a blob which is a pointer to the cursor.
-    */
-    sqlite3_result_blob(pContext, &pCsr, sizeof(pCsr), SQLITE_TRANSIENT);
-    rc = SQLITE_OK;
+    ** Return a blob which is a pointer to the cursor.  */
+    sqlite3_result_blob(pCtx, &pCsr, sizeof(pCsr), SQLITE_TRANSIENT);
+  }else if( iCol==p->nColumn+2 && pCsr->pExpr ){
+    sqlite3_result_int64(pCtx, pCsr->iLangid);
   }else{
+    /* The requested column is either a user column (one that contains 
+    ** indexed data), or the language-id column.  */
     rc = fts3CursorSeek(0, pCsr);
+
     if( rc==SQLITE_OK ){
-      sqlite3_result_value(pContext, sqlite3_column_value(pCsr->pStmt, iCol+1));
+      if( iCol==p->nColumn+2 ){
+        int iLangid = 0;
+        if( p->zLanguageid ){
+          iLangid = sqlite3_column_int(pCsr->pStmt, p->nColumn+1);
+        }
+        sqlite3_result_int(pCtx, iLangid);
+      }else if( sqlite3_data_count(pCsr->pStmt)>(iCol+1) ){
+        sqlite3_result_value(pCtx, sqlite3_column_value(pCsr->pStmt, iCol+1));
+      }
     }
   }
+
+  assert( ((Fts3Table *)pCsr->base.pVtab)->pSegments==0 );
   return rc;
 }
 
@@ -3193,8 +3280,42 @@ static int fts3UpdateMethod(
 ** hash-table to the database.
 */
 static int fts3SyncMethod(sqlite3_vtab *pVtab){
-  int rc = sqlite3Fts3PendingTermsFlush((Fts3Table *)pVtab);
-  sqlite3Fts3SegmentsClose((Fts3Table *)pVtab);
+
+  /* Following an incremental-merge operation, assuming that the input
+  ** segments are not completely consumed (the usual case), they are updated
+  ** in place to remove the entries that have already been merged. This
+  ** involves updating the leaf block that contains the smallest unmerged
+  ** entry and each block (if any) between the leaf and the root node. So
+  ** if the height of the input segment b-trees is N, and input segments
+  ** are merged eight at a time, updating the input segments at the end
+  ** of an incremental-merge requires writing (8*(1+N)) blocks. N is usually
+  ** small - often between 0 and 2. So the overhead of the incremental
+  ** merge is somewhere between 8 and 24 blocks. To avoid this overhead
+  ** dwarfing the actual productive work accomplished, the incremental merge
+  ** is only attempted if it will write at least 64 leaf blocks. Hence
+  ** nMinMerge.
+  **
+  ** Of course, updating the input segments also involves deleting a bunch
+  ** of blocks from the segments table. But this is not considered overhead
+  ** as it would also be required by a crisis-merge that used the same input 
+  ** segments.
+  */
+  const u32 nMinMerge = 64;       /* Minimum amount of incr-merge work to do */
+
+  Fts3Table *p = (Fts3Table*)pVtab;
+  int rc = sqlite3Fts3PendingTermsFlush(p);
+
+  if( rc==SQLITE_OK && p->bAutoincrmerge==1 && p->nLeafAdd>(nMinMerge/16) ){
+    int mxLevel = 0;              /* Maximum relative level value in db */
+    int A;                        /* Incr-merge parameter A */
+
+    rc = sqlite3Fts3MaxLevel(p, &mxLevel);
+    assert( rc==SQLITE_OK || mxLevel==0 );
+    A = p->nLeafAdd * mxLevel;
+    A += (A/2);
+    if( A>(int)nMinMerge ) rc = sqlite3Fts3Incrmerge(p, A, 8);
+  }
+  sqlite3Fts3SegmentsClose(p);
   return rc;
 }
 
@@ -3202,8 +3323,14 @@ static int fts3SyncMethod(sqlite3_vtab *pVtab){
 ** Implementation of xBegin() method. This is a no-op.
 */
 static int fts3BeginMethod(sqlite3_vtab *pVtab){
+  Fts3Table *p = (Fts3Table*)pVtab;
   UNUSED_PARAMETER(pVtab);
-  assert( ((Fts3Table *)pVtab)->nPendingData==0 );
+  assert( p->pSegments==0 );
+  assert( p->nPendingData==0 );
+  assert( p->inTransaction!=1 );
+  TESTONLY( p->inTransaction = 1 );
+  TESTONLY( p->mxSavepoint = -1; );
+  p->nLeafAdd = 0;
   return SQLITE_OK;
 }
 
@@ -3213,8 +3340,13 @@ static int fts3BeginMethod(sqlite3_vtab *pVtab){
 ** by fts3SyncMethod().
 */
 static int fts3CommitMethod(sqlite3_vtab *pVtab){
+  TESTONLY( Fts3Table *p = (Fts3Table*)pVtab );
   UNUSED_PARAMETER(pVtab);
-  assert( ((Fts3Table *)pVtab)->nPendingData==0 );
+  assert( p->nPendingData==0 );
+  assert( p->inTransaction!=0 );
+  assert( p->pSegments==0 );
+  TESTONLY( p->inTransaction = 0 );
+  TESTONLY( p->mxSavepoint = -1; );
   return SQLITE_OK;
 }
 
@@ -3223,93 +3355,31 @@ static int fts3CommitMethod(sqlite3_vtab *pVtab){
 ** hash-table. Any changes made to the database are reverted by SQLite.
 */
 static int fts3RollbackMethod(sqlite3_vtab *pVtab){
-  sqlite3Fts3PendingTermsClear((Fts3Table *)pVtab);
+  Fts3Table *p = (Fts3Table*)pVtab;
+  sqlite3Fts3PendingTermsClear(p);
+  assert( p->inTransaction!=0 );
+  TESTONLY( p->inTransaction = 0 );
+  TESTONLY( p->mxSavepoint = -1; );
   return SQLITE_OK;
 }
 
 /*
-** Load the doclist associated with expression pExpr to pExpr->aDoclist.
-** The loaded doclist contains positions as well as the document ids.
-** This is used by the matchinfo(), snippet() and offsets() auxillary
-** functions.
+** When called, *ppPoslist must point to the byte immediately following the
+** end of a position-list. i.e. ( (*ppPoslist)[-1]==POS_END ). This function
+** moves *ppPoslist so that it instead points to the first byte of the
+** same position list.
 */
-int sqlite3Fts3ExprLoadDoclist(Fts3Cursor *pCsr, Fts3Expr *pExpr){
-  int rc;
-  assert( pExpr->eType==FTSQUERY_PHRASE && pExpr->pPhrase );
-  assert( pCsr->eEvalmode==FTS3_EVAL_NEXT );
-  rc = fts3EvalExpr(pCsr, pExpr, &pExpr->aDoclist, &pExpr->nDoclist, 1);
-  return rc;
-}
-
-int sqlite3Fts3ExprLoadFtDoclist(
-  Fts3Cursor *pCsr, 
-  Fts3Expr *pExpr,
-  char **paDoclist,
-  int *pnDoclist
-){
-  int rc;
-  assert( pCsr->eEvalmode==FTS3_EVAL_NEXT );
-  assert( pExpr->eType==FTSQUERY_PHRASE && pExpr->pPhrase );
-  pCsr->eEvalmode = FTS3_EVAL_MATCHINFO;
-  rc = fts3EvalExpr(pCsr, pExpr, paDoclist, pnDoclist, 1);
-  pCsr->eEvalmode = FTS3_EVAL_NEXT;
-  return rc;
-}
+static void fts3ReversePoslist(char *pStart, char **ppPoslist){
+  char *p = &(*ppPoslist)[-2];
+  char c = 0;
 
-/*
-** After ExprLoadDoclist() (see above) has been called, this function is
-** used to iterate/search through the position lists that make up the doclist
-** stored in pExpr->aDoclist.
-*/
-char *sqlite3Fts3FindPositions(
-  Fts3Expr *pExpr,                /* Access this expressions doclist */
-  sqlite3_int64 iDocid,           /* Docid associated with requested pos-list */
-  int iCol                        /* Column of requested pos-list */
-){
-  assert( pExpr->isLoaded );
-  if( pExpr->aDoclist ){
-    char *pEnd = &pExpr->aDoclist[pExpr->nDoclist];
-    char *pCsr;
-
-    if( pExpr->pCurrent==0 ){
-      pExpr->pCurrent = pExpr->aDoclist;
-      pExpr->iCurrent = 0;
-      pExpr->pCurrent += sqlite3Fts3GetVarint(pExpr->pCurrent,&pExpr->iCurrent);
-    }
-    pCsr = pExpr->pCurrent;
-    assert( pCsr );
-
-    while( pCsr<pEnd ){
-      if( pExpr->iCurrent<iDocid ){
-        fts3PoslistCopy(0, &pCsr);
-        if( pCsr<pEnd ){
-          fts3GetDeltaVarint(&pCsr, &pExpr->iCurrent);
-        }
-        pExpr->pCurrent = pCsr;
-      }else{
-        if( pExpr->iCurrent==iDocid ){
-          int iThis = 0;
-          if( iCol<0 ){
-            /* If iCol is negative, return a pointer to the start of the
-            ** position-list (instead of a pointer to the start of a list
-            ** of offsets associated with a specific column).
-            */
-            return pCsr;
-          }
-          while( iThis<iCol ){
-            fts3ColumnlistCopy(0, &pCsr);
-            if( *pCsr==0x00 ) return 0;
-            pCsr++;
-            pCsr += sqlite3Fts3GetVarint32(pCsr, &iThis);
-          }
-          if( iCol==iThis && (*pCsr&0xFE) ) return pCsr;
-        }
-        return 0;
-      }
-    }
+  while( p>pStart && (c=*p--)==0 );
+  while( p>pStart && (*p & 0x80) | c ){ 
+    c = *p--; 
   }
-
-  return 0;
+  if( p>pStart ){ p = &p[2]; }
+  while( *p++&0x80 );
+  *ppPoslist = p;
 }
 
 /*
@@ -3510,15 +3580,22 @@ static int fts3RenameMethod(
   sqlite3 *db = p->db;            /* Database connection */
   int rc;                         /* Return Code */
 
+  /* As it happens, the pending terms table is always empty here. This is
+  ** because an "ALTER TABLE RENAME TABLE" statement inside a transaction 
+  ** always opens a savepoint transaction. And the xSavepoint() method 
+  ** flushes the pending terms table. But leave the (no-op) call to
+  ** PendingTermsFlush() in in case that changes.
+  */
+  assert( p->nPendingData==0 );
   rc = sqlite3Fts3PendingTermsFlush(p);
-  if( rc!=SQLITE_OK ){
-    return rc;
+
+  if( p->zContentTbl==0 ){
+    fts3DbExec(&rc, db,
+      "ALTER TABLE %Q.'%q_content'  RENAME TO '%q_content';",
+      p->zDb, p->zName, zName
+    );
   }
 
-  fts3DbExec(&rc, db,
-    "ALTER TABLE %Q.'%q_content'  RENAME TO '%q_content';",
-    p->zDb, p->zName, zName
-  );
   if( p->bHasDocsize ){
     fts3DbExec(&rc, db,
       "ALTER TABLE %Q.'%q_docsize'  RENAME TO '%q_docsize';",
@@ -3542,8 +3619,55 @@ static int fts3RenameMethod(
   return rc;
 }
 
+/*
+** The xSavepoint() method.
+**
+** Flush the contents of the pending-terms table to disk.
+*/
+static int fts3SavepointMethod(sqlite3_vtab *pVtab, int iSavepoint){
+  int rc = SQLITE_OK;
+  UNUSED_PARAMETER(iSavepoint);
+  assert( ((Fts3Table *)pVtab)->inTransaction );
+  assert( ((Fts3Table *)pVtab)->mxSavepoint < iSavepoint );
+  TESTONLY( ((Fts3Table *)pVtab)->mxSavepoint = iSavepoint );
+  if( ((Fts3Table *)pVtab)->bIgnoreSavepoint==0 ){
+    rc = fts3SyncMethod(pVtab);
+  }
+  return rc;
+}
+
+/*
+** The xRelease() method.
+**
+** This is a no-op.
+*/
+static int fts3ReleaseMethod(sqlite3_vtab *pVtab, int iSavepoint){
+  TESTONLY( Fts3Table *p = (Fts3Table*)pVtab );
+  UNUSED_PARAMETER(iSavepoint);
+  UNUSED_PARAMETER(pVtab);
+  assert( p->inTransaction );
+  assert( p->mxSavepoint >= iSavepoint );
+  TESTONLY( p->mxSavepoint = iSavepoint-1 );
+  return SQLITE_OK;
+}
+
+/*
+** The xRollbackTo() method.
+**
+** Discard the contents of the pending terms table.
+*/
+static int fts3RollbackToMethod(sqlite3_vtab *pVtab, int iSavepoint){
+  Fts3Table *p = (Fts3Table*)pVtab;
+  UNUSED_PARAMETER(iSavepoint);
+  assert( p->inTransaction );
+  assert( p->mxSavepoint >= iSavepoint );
+  TESTONLY( p->mxSavepoint = iSavepoint );
+  sqlite3Fts3PendingTermsClear(p);
+  return SQLITE_OK;
+}
+
 static const sqlite3_module fts3Module = {
-  /* iVersion      */ 0,
+  /* iVersion      */ 2,
   /* xCreate       */ fts3CreateMethod,
   /* xConnect      */ fts3ConnectMethod,
   /* xBestIndex    */ fts3BestIndexMethod,
@@ -3563,6 +3687,9 @@ static const sqlite3_module fts3Module = {
   /* xRollback     */ fts3RollbackMethod,
   /* xFindFunction */ fts3FindFunctionMethod,
   /* xRename */       fts3RenameMethod,
+  /* xSavepoint    */ fts3SavepointMethod,
+  /* xRelease      */ fts3ReleaseMethod,
+  /* xRollbackTo   */ fts3RollbackToMethod,
 };
 
 /*
@@ -3588,12 +3715,15 @@ static void hashDestroy(void *p){
 */
 void sqlite3Fts3SimpleTokenizerModule(sqlite3_tokenizer_module const**ppModule);
 void sqlite3Fts3PorterTokenizerModule(sqlite3_tokenizer_module const**ppModule);
+#ifdef SQLITE_ENABLE_FTS4_UNICODE61
+void sqlite3Fts3UnicodeTokenizer(sqlite3_tokenizer_module const**ppModule);
+#endif
 #ifdef SQLITE_ENABLE_ICU
 void sqlite3Fts3IcuTokenizerModule(sqlite3_tokenizer_module const**ppModule);
 #endif
 
 /*
-** Initialise the fts3 extension. If this extension is built as part
+** Initialize the fts3 extension. If this extension is built as part
 ** of the sqlite library, then this function is called directly by
 ** SQLite. If fts3 is built as a dynamically loadable extension, this
 ** function is called by the sqlite3_extension_init() entry point.
@@ -3603,19 +3733,31 @@ int sqlite3Fts3Init(sqlite3 *db){
   Fts3Hash *pHash = 0;
   const sqlite3_tokenizer_module *pSimple = 0;
   const sqlite3_tokenizer_module *pPorter = 0;
+#ifdef SQLITE_ENABLE_FTS4_UNICODE61
+  const sqlite3_tokenizer_module *pUnicode = 0;
+#endif
 
 #ifdef SQLITE_ENABLE_ICU
   const sqlite3_tokenizer_module *pIcu = 0;
   sqlite3Fts3IcuTokenizerModule(&pIcu);
 #endif
 
+#ifdef SQLITE_ENABLE_FTS4_UNICODE61
+  sqlite3Fts3UnicodeTokenizer(&pUnicode);
+#endif
+
+#ifdef SQLITE_TEST
+  rc = sqlite3Fts3InitTerm(db);
+  if( rc!=SQLITE_OK ) return rc;
+#endif
+
   rc = sqlite3Fts3InitAux(db);
   if( rc!=SQLITE_OK ) return rc;
 
   sqlite3Fts3SimpleTokenizerModule(&pSimple);
   sqlite3Fts3PorterTokenizerModule(&pPorter);
 
-  /* Allocate and initialise the hash-table used to store tokenizers. */
+  /* Allocate and initialize the hash-table used to store tokenizers. */
   pHash = sqlite3_malloc(sizeof(Fts3Hash));
   if( !pHash ){
     rc = SQLITE_NOMEM;
@@ -3627,6 +3769,10 @@ int sqlite3Fts3Init(sqlite3 *db){
   if( rc==SQLITE_OK ){
     if( sqlite3Fts3HashInsert(pHash, "simple", 7, (void *)pSimple)
      || sqlite3Fts3HashInsert(pHash, "porter", 7, (void *)pPorter) 
+
+#ifdef SQLITE_ENABLE_FTS4_UNICODE61
+     || sqlite3Fts3HashInsert(pHash, "unicode61", 10, (void *)pUnicode) 
+#endif
 #ifdef SQLITE_ENABLE_ICU
      || (pIcu && sqlite3Fts3HashInsert(pHash, "icu", 4, (void *)pIcu))
 #endif
@@ -3661,9 +3807,13 @@ int sqlite3Fts3Init(sqlite3 *db){
           db, "fts4", &fts3Module, (void *)pHash, 0
       );
     }
+    if( rc==SQLITE_OK ){
+      rc = sqlite3Fts3InitTok(db, (void *)pHash);
+    }
     return rc;
   }
 
+
   /* An error has occurred. Delete the hash table and return the error code. */
   assert( rc!=SQLITE_OK );
   if( pHash ){
@@ -3673,8 +3823,1935 @@ int sqlite3Fts3Init(sqlite3 *db){
   return rc;
 }
 
+/*
+** Allocate an Fts3MultiSegReader for each token in the expression headed
+** by pExpr. 
+**
+** An Fts3SegReader object is a cursor that can seek or scan a range of
+** entries within a single segment b-tree. An Fts3MultiSegReader uses multiple
+** Fts3SegReader objects internally to provide an interface to seek or scan
+** within the union of all segments of a b-tree. Hence the name.
+**
+** If the allocated Fts3MultiSegReader just seeks to a single entry in a
+** segment b-tree (if the term is not a prefix or it is a prefix for which
+** there exists prefix b-tree of the right length) then it may be traversed
+** and merged incrementally. Otherwise, it has to be merged into an in-memory 
+** doclist and then traversed.
+*/
+static void fts3EvalAllocateReaders(
+  Fts3Cursor *pCsr,               /* FTS cursor handle */
+  Fts3Expr *pExpr,                /* Allocate readers for this expression */
+  int *pnToken,                   /* OUT: Total number of tokens in phrase. */
+  int *pnOr,                      /* OUT: Total number of OR nodes in expr. */
+  int *pRc                        /* IN/OUT: Error code */
+){
+  if( pExpr && SQLITE_OK==*pRc ){
+    if( pExpr->eType==FTSQUERY_PHRASE ){
+      int i;
+      int nToken = pExpr->pPhrase->nToken;
+      *pnToken += nToken;
+      for(i=0; i<nToken; i++){
+        Fts3PhraseToken *pToken = &pExpr->pPhrase->aToken[i];
+        int rc = fts3TermSegReaderCursor(pCsr, 
+            pToken->z, pToken->n, pToken->isPrefix, &pToken->pSegcsr
+        );
+        if( rc!=SQLITE_OK ){
+          *pRc = rc;
+          return;
+        }
+      }
+      assert( pExpr->pPhrase->iDoclistToken==0 );
+      pExpr->pPhrase->iDoclistToken = -1;
+    }else{
+      *pnOr += (pExpr->eType==FTSQUERY_OR);
+      fts3EvalAllocateReaders(pCsr, pExpr->pLeft, pnToken, pnOr, pRc);
+      fts3EvalAllocateReaders(pCsr, pExpr->pRight, pnToken, pnOr, pRc);
+    }
+  }
+}
+
+/*
+** Arguments pList/nList contain the doclist for token iToken of phrase p.
+** It is merged into the main doclist stored in p->doclist.aAll/nAll.
+**
+** This function assumes that pList points to a buffer allocated using
+** sqlite3_malloc(). This function takes responsibility for eventually
+** freeing the buffer.
+*/
+static void fts3EvalPhraseMergeToken(
+  Fts3Table *pTab,                /* FTS Table pointer */
+  Fts3Phrase *p,                  /* Phrase to merge pList/nList into */
+  int iToken,                     /* Token pList/nList corresponds to */
+  char *pList,                    /* Pointer to doclist */
+  int nList                       /* Number of bytes in pList */
+){
+  assert( iToken!=p->iDoclistToken );
+
+  if( pList==0 ){
+    sqlite3_free(p->doclist.aAll);
+    p->doclist.aAll = 0;
+    p->doclist.nAll = 0;
+  }
+
+  else if( p->iDoclistToken<0 ){
+    p->doclist.aAll = pList;
+    p->doclist.nAll = nList;
+  }
+
+  else if( p->doclist.aAll==0 ){
+    sqlite3_free(pList);
+  }
+
+  else {
+    char *pLeft;
+    char *pRight;
+    int nLeft;
+    int nRight;
+    int nDiff;
+
+    if( p->iDoclistToken<iToken ){
+      pLeft = p->doclist.aAll;
+      nLeft = p->doclist.nAll;
+      pRight = pList;
+      nRight = nList;
+      nDiff = iToken - p->iDoclistToken;
+    }else{
+      pRight = p->doclist.aAll;
+      nRight = p->doclist.nAll;
+      pLeft = pList;
+      nLeft = nList;
+      nDiff = p->iDoclistToken - iToken;
+    }
+
+    fts3DoclistPhraseMerge(pTab->bDescIdx, nDiff, pLeft, nLeft, pRight,&nRight);
+    sqlite3_free(pLeft);
+    p->doclist.aAll = pRight;
+    p->doclist.nAll = nRight;
+  }
+
+  if( iToken>p->iDoclistToken ) p->iDoclistToken = iToken;
+}
+
+/*
+** Load the doclist for phrase p into p->doclist.aAll/nAll. The loaded doclist
+** does not take deferred tokens into account.
+**
+** SQLITE_OK is returned if no error occurs, otherwise an SQLite error code.
+*/
+static int fts3EvalPhraseLoad(
+  Fts3Cursor *pCsr,               /* FTS Cursor handle */
+  Fts3Phrase *p                   /* Phrase object */
+){
+  Fts3Table *pTab = (Fts3Table *)pCsr->base.pVtab;
+  int iToken;
+  int rc = SQLITE_OK;
+
+  for(iToken=0; rc==SQLITE_OK && iToken<p->nToken; iToken++){
+    Fts3PhraseToken *pToken = &p->aToken[iToken];
+    assert( pToken->pDeferred==0 || pToken->pSegcsr==0 );
+
+    if( pToken->pSegcsr ){
+      int nThis = 0;
+      char *pThis = 0;
+      rc = fts3TermSelect(pTab, pToken, p->iColumn, &nThis, &pThis);
+      if( rc==SQLITE_OK ){
+        fts3EvalPhraseMergeToken(pTab, p, iToken, pThis, nThis);
+      }
+    }
+    assert( pToken->pSegcsr==0 );
+  }
+
+  return rc;
+}
+
+/*
+** This function is called on each phrase after the position lists for
+** any deferred tokens have been loaded into memory. It updates the phrases
+** current position list to include only those positions that are really
+** instances of the phrase (after considering deferred tokens). If this
+** means that the phrase does not appear in the current row, doclist.pList
+** and doclist.nList are both zeroed.
+**
+** SQLITE_OK is returned if no error occurs, otherwise an SQLite error code.
+*/
+static int fts3EvalDeferredPhrase(Fts3Cursor *pCsr, Fts3Phrase *pPhrase){
+  int iToken;                     /* Used to iterate through phrase tokens */
+  char *aPoslist = 0;             /* Position list for deferred tokens */
+  int nPoslist = 0;               /* Number of bytes in aPoslist */
+  int iPrev = -1;                 /* Token number of previous deferred token */
+
+  assert( pPhrase->doclist.bFreeList==0 );
+
+  for(iToken=0; iToken<pPhrase->nToken; iToken++){
+    Fts3PhraseToken *pToken = &pPhrase->aToken[iToken];
+    Fts3DeferredToken *pDeferred = pToken->pDeferred;
+
+    if( pDeferred ){
+      char *pList;
+      int nList;
+      int rc = sqlite3Fts3DeferredTokenList(pDeferred, &pList, &nList);
+      if( rc!=SQLITE_OK ) return rc;
+
+      if( pList==0 ){
+        sqlite3_free(aPoslist);
+        pPhrase->doclist.pList = 0;
+        pPhrase->doclist.nList = 0;
+        return SQLITE_OK;
+
+      }else if( aPoslist==0 ){
+        aPoslist = pList;
+        nPoslist = nList;
+
+      }else{
+        char *aOut = pList;
+        char *p1 = aPoslist;
+        char *p2 = aOut;
+
+        assert( iPrev>=0 );
+        fts3PoslistPhraseMerge(&aOut, iToken-iPrev, 0, 1, &p1, &p2);
+        sqlite3_free(aPoslist);
+        aPoslist = pList;
+        nPoslist = (int)(aOut - aPoslist);
+        if( nPoslist==0 ){
+          sqlite3_free(aPoslist);
+          pPhrase->doclist.pList = 0;
+          pPhrase->doclist.nList = 0;
+          return SQLITE_OK;
+        }
+      }
+      iPrev = iToken;
+    }
+  }
+
+  if( iPrev>=0 ){
+    int nMaxUndeferred = pPhrase->iDoclistToken;
+    if( nMaxUndeferred<0 ){
+      pPhrase->doclist.pList = aPoslist;
+      pPhrase->doclist.nList = nPoslist;
+      pPhrase->doclist.iDocid = pCsr->iPrevId;
+      pPhrase->doclist.bFreeList = 1;
+    }else{
+      int nDistance;
+      char *p1;
+      char *p2;
+      char *aOut;
+
+      if( nMaxUndeferred>iPrev ){
+        p1 = aPoslist;
+        p2 = pPhrase->doclist.pList;
+        nDistance = nMaxUndeferred - iPrev;
+      }else{
+        p1 = pPhrase->doclist.pList;
+        p2 = aPoslist;
+        nDistance = iPrev - nMaxUndeferred;
+      }
+
+      aOut = (char *)sqlite3_malloc(nPoslist+8);
+      if( !aOut ){
+        sqlite3_free(aPoslist);
+        return SQLITE_NOMEM;
+      }
+      
+      pPhrase->doclist.pList = aOut;
+      if( fts3PoslistPhraseMerge(&aOut, nDistance, 0, 1, &p1, &p2) ){
+        pPhrase->doclist.bFreeList = 1;
+        pPhrase->doclist.nList = (int)(aOut - pPhrase->doclist.pList);
+      }else{
+        sqlite3_free(aOut);
+        pPhrase->doclist.pList = 0;
+        pPhrase->doclist.nList = 0;
+      }
+      sqlite3_free(aPoslist);
+    }
+  }
+
+  return SQLITE_OK;
+}
+
+/*
+** Maximum number of tokens a phrase may have to be considered for the
+** incremental doclists strategy.
+*/
+#define MAX_INCR_PHRASE_TOKENS 4
+
+/*
+** This function is called for each Fts3Phrase in a full-text query 
+** expression to initialize the mechanism for returning rows. Once this
+** function has been called successfully on an Fts3Phrase, it may be
+** used with fts3EvalPhraseNext() to iterate through the matching docids.
+**
+** If parameter bOptOk is true, then the phrase may (or may not) use the
+** incremental loading strategy. Otherwise, the entire doclist is loaded into
+** memory within this call.
+**
+** SQLITE_OK is returned if no error occurs, otherwise an SQLite error code.
+*/
+static int fts3EvalPhraseStart(Fts3Cursor *pCsr, int bOptOk, Fts3Phrase *p){
+  Fts3Table *pTab = (Fts3Table *)pCsr->base.pVtab;
+  int rc = SQLITE_OK;             /* Error code */
+  int i;
+
+  /* Determine if doclists may be loaded from disk incrementally. This is
+  ** possible if the bOptOk argument is true, the FTS doclists will be
+  ** scanned in forward order, and the phrase consists of 
+  ** MAX_INCR_PHRASE_TOKENS or fewer tokens, none of which are are "^first"
+  ** tokens or prefix tokens that cannot use a prefix-index.  */
+  int bHaveIncr = 0;
+  int bIncrOk = (bOptOk 
+   && pCsr->bDesc==pTab->bDescIdx 
+   && p->nToken<=MAX_INCR_PHRASE_TOKENS && p->nToken>0
+   && p->nToken<=MAX_INCR_PHRASE_TOKENS && p->nToken>0
+#ifdef SQLITE_TEST
+   && pTab->bNoIncrDoclist==0
+#endif
+  );
+  for(i=0; bIncrOk==1 && i<p->nToken; i++){
+    Fts3PhraseToken *pToken = &p->aToken[i];
+    if( pToken->bFirst || (pToken->pSegcsr!=0 && !pToken->pSegcsr->bLookup) ){
+      bIncrOk = 0;
+    }
+    if( pToken->pSegcsr ) bHaveIncr = 1;
+  }
+
+  if( bIncrOk && bHaveIncr ){
+    /* Use the incremental approach. */
+    int iCol = (p->iColumn >= pTab->nColumn ? -1 : p->iColumn);
+    for(i=0; rc==SQLITE_OK && i<p->nToken; i++){
+      Fts3PhraseToken *pToken = &p->aToken[i];
+      Fts3MultiSegReader *pSegcsr = pToken->pSegcsr;
+      if( pSegcsr ){
+        rc = sqlite3Fts3MsrIncrStart(pTab, pSegcsr, iCol, pToken->z, pToken->n);
+      }
+    }
+    p->bIncr = 1;
+  }else{
+    /* Load the full doclist for the phrase into memory. */
+    rc = fts3EvalPhraseLoad(pCsr, p);
+    p->bIncr = 0;
+  }
+
+  assert( rc!=SQLITE_OK || p->nToken<1 || p->aToken[0].pSegcsr==0 || p->bIncr );
+  return rc;
+}
+
+/*
+** This function is used to iterate backwards (from the end to start) 
+** through doclists. It is used by this module to iterate through phrase
+** doclists in reverse and by the fts3_write.c module to iterate through
+** pending-terms lists when writing to databases with "order=desc".
+**
+** The doclist may be sorted in ascending (parameter bDescIdx==0) or 
+** descending (parameter bDescIdx==1) order of docid. Regardless, this
+** function iterates from the end of the doclist to the beginning.
+*/
+void sqlite3Fts3DoclistPrev(
+  int bDescIdx,                   /* True if the doclist is desc */
+  char *aDoclist,                 /* Pointer to entire doclist */
+  int nDoclist,                   /* Length of aDoclist in bytes */
+  char **ppIter,                  /* IN/OUT: Iterator pointer */
+  sqlite3_int64 *piDocid,         /* IN/OUT: Docid pointer */
+  int *pnList,                    /* OUT: List length pointer */
+  u8 *pbEof                       /* OUT: End-of-file flag */
+){
+  char *p = *ppIter;
+
+  assert( nDoclist>0 );
+  assert( *pbEof==0 );
+  assert( p || *piDocid==0 );
+  assert( !p || (p>aDoclist && p<&aDoclist[nDoclist]) );
+
+  if( p==0 ){
+    sqlite3_int64 iDocid = 0;
+    char *pNext = 0;
+    char *pDocid = aDoclist;
+    char *pEnd = &aDoclist[nDoclist];
+    int iMul = 1;
+
+    while( pDocid<pEnd ){
+      sqlite3_int64 iDelta;
+      pDocid += sqlite3Fts3GetVarint(pDocid, &iDelta);
+      iDocid += (iMul * iDelta);
+      pNext = pDocid;
+      fts3PoslistCopy(0, &pDocid);
+      while( pDocid<pEnd && *pDocid==0 ) pDocid++;
+      iMul = (bDescIdx ? -1 : 1);
+    }
+
+    *pnList = (int)(pEnd - pNext);
+    *ppIter = pNext;
+    *piDocid = iDocid;
+  }else{
+    int iMul = (bDescIdx ? -1 : 1);
+    sqlite3_int64 iDelta;
+    fts3GetReverseVarint(&p, aDoclist, &iDelta);
+    *piDocid -= (iMul * iDelta);
+
+    if( p==aDoclist ){
+      *pbEof = 1;
+    }else{
+      char *pSave = p;
+      fts3ReversePoslist(aDoclist, &p);
+      *pnList = (int)(pSave - p);
+    }
+    *ppIter = p;
+  }
+}
+
+/*
+** Iterate forwards through a doclist.
+*/
+void sqlite3Fts3DoclistNext(
+  int bDescIdx,                   /* True if the doclist is desc */
+  char *aDoclist,                 /* Pointer to entire doclist */
+  int nDoclist,                   /* Length of aDoclist in bytes */
+  char **ppIter,                  /* IN/OUT: Iterator pointer */
+  sqlite3_int64 *piDocid,         /* IN/OUT: Docid pointer */
+  u8 *pbEof                       /* OUT: End-of-file flag */
+){
+  char *p = *ppIter;
+
+  assert( nDoclist>0 );
+  assert( *pbEof==0 );
+  assert( p || *piDocid==0 );
+  assert( !p || (p>=aDoclist && p<=&aDoclist[nDoclist]) );
+
+  if( p==0 ){
+    p = aDoclist;
+    p += sqlite3Fts3GetVarint(p, piDocid);
+  }else{
+    fts3PoslistCopy(0, &p);
+    if( p>=&aDoclist[nDoclist] ){
+      *pbEof = 1;
+    }else{
+      sqlite3_int64 iVar;
+      p += sqlite3Fts3GetVarint(p, &iVar);
+      *piDocid += ((bDescIdx ? -1 : 1) * iVar);
+    }
+  }
+
+  *ppIter = p;
+}
+
+/*
+** Advance the iterator pDL to the next entry in pDL->aAll/nAll. Set *pbEof
+** to true if EOF is reached.
+*/
+static void fts3EvalDlPhraseNext(
+  Fts3Table *pTab,
+  Fts3Doclist *pDL,
+  u8 *pbEof
+){
+  char *pIter;                            /* Used to iterate through aAll */
+  char *pEnd = &pDL->aAll[pDL->nAll];     /* 1 byte past end of aAll */
+ 
+  if( pDL->pNextDocid ){
+    pIter = pDL->pNextDocid;
+  }else{
+    pIter = pDL->aAll;
+  }
+
+  if( pIter>=pEnd ){
+    /* We have already reached the end of this doclist. EOF. */
+    *pbEof = 1;
+  }else{
+    sqlite3_int64 iDelta;
+    pIter += sqlite3Fts3GetVarint(pIter, &iDelta);
+    if( pTab->bDescIdx==0 || pDL->pNextDocid==0 ){
+      pDL->iDocid += iDelta;
+    }else{
+      pDL->iDocid -= iDelta;
+    }
+    pDL->pList = pIter;
+    fts3PoslistCopy(0, &pIter);
+    pDL->nList = (int)(pIter - pDL->pList);
+
+    /* pIter now points just past the 0x00 that terminates the position-
+    ** list for document pDL->iDocid. However, if this position-list was
+    ** edited in place by fts3EvalNearTrim(), then pIter may not actually
+    ** point to the start of the next docid value. The following line deals
+    ** with this case by advancing pIter past the zero-padding added by
+    ** fts3EvalNearTrim().  */
+    while( pIter<pEnd && *pIter==0 ) pIter++;
+
+    pDL->pNextDocid = pIter;
+    assert( pIter>=&pDL->aAll[pDL->nAll] || *pIter );
+    *pbEof = 0;
+  }
+}
+
+/*
+** Helper type used by fts3EvalIncrPhraseNext() and incrPhraseTokenNext().
+*/
+typedef struct TokenDoclist TokenDoclist;
+struct TokenDoclist {
+  int bIgnore;
+  sqlite3_int64 iDocid;
+  char *pList;
+  int nList;
+};
+
+/*
+** Token pToken is an incrementally loaded token that is part of a 
+** multi-token phrase. Advance it to the next matching document in the
+** database and populate output variable *p with the details of the new
+** entry. Or, if the iterator has reached EOF, set *pbEof to true.
+**
+** If an error occurs, return an SQLite error code. Otherwise, return 
+** SQLITE_OK.
+*/
+static int incrPhraseTokenNext(
+  Fts3Table *pTab,                /* Virtual table handle */
+  Fts3Phrase *pPhrase,            /* Phrase to advance token of */
+  int iToken,                     /* Specific token to advance */
+  TokenDoclist *p,                /* OUT: Docid and doclist for new entry */
+  u8 *pbEof                       /* OUT: True if iterator is at EOF */
+){
+  int rc = SQLITE_OK;
+
+  if( pPhrase->iDoclistToken==iToken ){
+    assert( p->bIgnore==0 );
+    assert( pPhrase->aToken[iToken].pSegcsr==0 );
+    fts3EvalDlPhraseNext(pTab, &pPhrase->doclist, pbEof);
+    p->pList = pPhrase->doclist.pList;
+    p->nList = pPhrase->doclist.nList;
+    p->iDocid = pPhrase->doclist.iDocid;
+  }else{
+    Fts3PhraseToken *pToken = &pPhrase->aToken[iToken];
+    assert( pToken->pDeferred==0 );
+    assert( pToken->pSegcsr || pPhrase->iDoclistToken>=0 );
+    if( pToken->pSegcsr ){
+      assert( p->bIgnore==0 );
+      rc = sqlite3Fts3MsrIncrNext(
+          pTab, pToken->pSegcsr, &p->iDocid, &p->pList, &p->nList
+      );
+      if( p->pList==0 ) *pbEof = 1;
+    }else{
+      p->bIgnore = 1;
+    }
+  }
+
+  return rc;
+}
+
+
+/*
+** The phrase iterator passed as the second argument:
+**
+**   * features at least one token that uses an incremental doclist, and 
+**
+**   * does not contain any deferred tokens.
+**
+** Advance it to the next matching documnent in the database and populate
+** the Fts3Doclist.pList and nList fields. 
+**
+** If there is no "next" entry and no error occurs, then *pbEof is set to
+** 1 before returning. Otherwise, if no error occurs and the iterator is
+** successfully advanced, *pbEof is set to 0.
+**
+** If an error occurs, return an SQLite error code. Otherwise, return 
+** SQLITE_OK.
+*/
+static int fts3EvalIncrPhraseNext(
+  Fts3Cursor *pCsr,               /* FTS Cursor handle */
+  Fts3Phrase *p,                  /* Phrase object to advance to next docid */
+  u8 *pbEof                       /* OUT: Set to 1 if EOF */
+){
+  int rc = SQLITE_OK;
+  Fts3Doclist *pDL = &p->doclist;
+  Fts3Table *pTab = (Fts3Table *)pCsr->base.pVtab;
+  u8 bEof = 0;
+
+  /* This is only called if it is guaranteed that the phrase has at least
+  ** one incremental token. In which case the bIncr flag is set. */
+  assert( p->bIncr==1 );
+
+  if( p->nToken==1 && p->bIncr ){
+    rc = sqlite3Fts3MsrIncrNext(pTab, p->aToken[0].pSegcsr, 
+        &pDL->iDocid, &pDL->pList, &pDL->nList
+    );
+    if( pDL->pList==0 ) bEof = 1;
+  }else{
+    int bDescDoclist = pCsr->bDesc;
+    struct TokenDoclist a[MAX_INCR_PHRASE_TOKENS];
+
+    memset(a, 0, sizeof(a));
+    assert( p->nToken<=MAX_INCR_PHRASE_TOKENS );
+    assert( p->iDoclistToken<MAX_INCR_PHRASE_TOKENS );
+
+    while( bEof==0 ){
+      int bMaxSet = 0;
+      sqlite3_int64 iMax = 0;     /* Largest docid for all iterators */
+      int i;                      /* Used to iterate through tokens */
+
+      /* Advance the iterator for each token in the phrase once. */
+      for(i=0; rc==SQLITE_OK && i<p->nToken && bEof==0; i++){
+        rc = incrPhraseTokenNext(pTab, p, i, &a[i], &bEof);
+        if( a[i].bIgnore==0 && (bMaxSet==0 || DOCID_CMP(iMax, a[i].iDocid)<0) ){
+          iMax = a[i].iDocid;
+          bMaxSet = 1;
+        }
+      }
+      assert( rc!=SQLITE_OK || a[p->nToken-1].bIgnore==0 );
+      assert( rc!=SQLITE_OK || bMaxSet );
+
+      /* Keep advancing iterators until they all point to the same document */
+      for(i=0; i<p->nToken; i++){
+        while( rc==SQLITE_OK && bEof==0 
+            && a[i].bIgnore==0 && DOCID_CMP(a[i].iDocid, iMax)<0 
+        ){
+          rc = incrPhraseTokenNext(pTab, p, i, &a[i], &bEof);
+          if( DOCID_CMP(a[i].iDocid, iMax)>0 ){
+            iMax = a[i].iDocid;
+            i = 0;
+          }
+        }
+      }
+
+      /* Check if the current entries really are a phrase match */
+      if( bEof==0 ){
+        int nList = 0;
+        int nByte = a[p->nToken-1].nList;
+        char *aDoclist = sqlite3_malloc(nByte+1);
+        if( !aDoclist ) return SQLITE_NOMEM;
+        memcpy(aDoclist, a[p->nToken-1].pList, nByte+1);
+
+        for(i=0; i<(p->nToken-1); i++){
+          if( a[i].bIgnore==0 ){
+            char *pL = a[i].pList;
+            char *pR = aDoclist;
+            char *pOut = aDoclist;
+            int nDist = p->nToken-1-i;
+            int res = fts3PoslistPhraseMerge(&pOut, nDist, 0, 1, &pL, &pR);
+            if( res==0 ) break;
+            nList = (int)(pOut - aDoclist);
+          }
+        }
+        if( i==(p->nToken-1) ){
+          pDL->iDocid = iMax;
+          pDL->pList = aDoclist;
+          pDL->nList = nList;
+          pDL->bFreeList = 1;
+          break;
+        }
+        sqlite3_free(aDoclist);
+      }
+    }
+  }
+
+  *pbEof = bEof;
+  return rc;
+}
+
+/*
+** Attempt to move the phrase iterator to point to the next matching docid. 
+** If an error occurs, return an SQLite error code. Otherwise, return 
+** SQLITE_OK.
+**
+** If there is no "next" entry and no error occurs, then *pbEof is set to
+** 1 before returning. Otherwise, if no error occurs and the iterator is
+** successfully advanced, *pbEof is set to 0.
+*/
+static int fts3EvalPhraseNext(
+  Fts3Cursor *pCsr,               /* FTS Cursor handle */
+  Fts3Phrase *p,                  /* Phrase object to advance to next docid */
+  u8 *pbEof                       /* OUT: Set to 1 if EOF */
+){
+  int rc = SQLITE_OK;
+  Fts3Doclist *pDL = &p->doclist;
+  Fts3Table *pTab = (Fts3Table *)pCsr->base.pVtab;
+
+  if( p->bIncr ){
+    rc = fts3EvalIncrPhraseNext(pCsr, p, pbEof);
+  }else if( pCsr->bDesc!=pTab->bDescIdx && pDL->nAll ){
+    sqlite3Fts3DoclistPrev(pTab->bDescIdx, pDL->aAll, pDL->nAll, 
+        &pDL->pNextDocid, &pDL->iDocid, &pDL->nList, pbEof
+    );
+    pDL->pList = pDL->pNextDocid;
+  }else{
+    fts3EvalDlPhraseNext(pTab, pDL, pbEof);
+  }
+
+  return rc;
+}
+
+/*
+**
+** If *pRc is not SQLITE_OK when this function is called, it is a no-op.
+** Otherwise, fts3EvalPhraseStart() is called on all phrases within the
+** expression. Also the Fts3Expr.bDeferred variable is set to true for any
+** expressions for which all descendent tokens are deferred.
+**
+** If parameter bOptOk is zero, then it is guaranteed that the
+** Fts3Phrase.doclist.aAll/nAll variables contain the entire doclist for
+** each phrase in the expression (subject to deferred token processing).
+** Or, if bOptOk is non-zero, then one or more tokens within the expression
+** may be loaded incrementally, meaning doclist.aAll/nAll is not available.
+**
+** If an error occurs within this function, *pRc is set to an SQLite error
+** code before returning.
+*/
+static void fts3EvalStartReaders(
+  Fts3Cursor *pCsr,               /* FTS Cursor handle */
+  Fts3Expr *pExpr,                /* Expression to initialize phrases in */
+  int *pRc                        /* IN/OUT: Error code */
+){
+  if( pExpr && SQLITE_OK==*pRc ){
+    if( pExpr->eType==FTSQUERY_PHRASE ){
+      int i;
+      int nToken = pExpr->pPhrase->nToken;
+      for(i=0; i<nToken; i++){
+        if( pExpr->pPhrase->aToken[i].pDeferred==0 ) break;
+      }
+      pExpr->bDeferred = (i==nToken);
+      *pRc = fts3EvalPhraseStart(pCsr, 1, pExpr->pPhrase);
+    }else{
+      fts3EvalStartReaders(pCsr, pExpr->pLeft, pRc);
+      fts3EvalStartReaders(pCsr, pExpr->pRight, pRc);
+      pExpr->bDeferred = (pExpr->pLeft->bDeferred && pExpr->pRight->bDeferred);
+    }
+  }
+}
+
+/*
+** An array of the following structures is assembled as part of the process
+** of selecting tokens to defer before the query starts executing (as part
+** of the xFilter() method). There is one element in the array for each
+** token in the FTS expression.
+**
+** Tokens are divided into AND/NEAR clusters. All tokens in a cluster belong
+** to phrases that are connected only by AND and NEAR operators (not OR or
+** NOT). When determining tokens to defer, each AND/NEAR cluster is considered
+** separately. The root of a tokens AND/NEAR cluster is stored in 
+** Fts3TokenAndCost.pRoot.
+*/
+typedef struct Fts3TokenAndCost Fts3TokenAndCost;
+struct Fts3TokenAndCost {
+  Fts3Phrase *pPhrase;            /* The phrase the token belongs to */
+  int iToken;                     /* Position of token in phrase */
+  Fts3PhraseToken *pToken;        /* The token itself */
+  Fts3Expr *pRoot;                /* Root of NEAR/AND cluster */
+  int nOvfl;                      /* Number of overflow pages to load doclist */
+  int iCol;                       /* The column the token must match */
+};
+
+/*
+** This function is used to populate an allocated Fts3TokenAndCost array.
+**
+** If *pRc is not SQLITE_OK when this function is called, it is a no-op.
+** Otherwise, if an error occurs during execution, *pRc is set to an
+** SQLite error code.
+*/
+static void fts3EvalTokenCosts(
+  Fts3Cursor *pCsr,               /* FTS Cursor handle */
+  Fts3Expr *pRoot,                /* Root of current AND/NEAR cluster */
+  Fts3Expr *pExpr,                /* Expression to consider */
+  Fts3TokenAndCost **ppTC,        /* Write new entries to *(*ppTC)++ */
+  Fts3Expr ***ppOr,               /* Write new OR root to *(*ppOr)++ */
+  int *pRc                        /* IN/OUT: Error code */
+){
+  if( *pRc==SQLITE_OK ){
+    if( pExpr->eType==FTSQUERY_PHRASE ){
+      Fts3Phrase *pPhrase = pExpr->pPhrase;
+      int i;
+      for(i=0; *pRc==SQLITE_OK && i<pPhrase->nToken; i++){
+        Fts3TokenAndCost *pTC = (*ppTC)++;
+        pTC->pPhrase = pPhrase;
+        pTC->iToken = i;
+        pTC->pRoot = pRoot;
+        pTC->pToken = &pPhrase->aToken[i];
+        pTC->iCol = pPhrase->iColumn;
+        *pRc = sqlite3Fts3MsrOvfl(pCsr, pTC->pToken->pSegcsr, &pTC->nOvfl);
+      }
+    }else if( pExpr->eType!=FTSQUERY_NOT ){
+      assert( pExpr->eType==FTSQUERY_OR
+           || pExpr->eType==FTSQUERY_AND
+           || pExpr->eType==FTSQUERY_NEAR
+      );
+      assert( pExpr->pLeft && pExpr->pRight );
+      if( pExpr->eType==FTSQUERY_OR ){
+        pRoot = pExpr->pLeft;
+        **ppOr = pRoot;
+        (*ppOr)++;
+      }
+      fts3EvalTokenCosts(pCsr, pRoot, pExpr->pLeft, ppTC, ppOr, pRc);
+      if( pExpr->eType==FTSQUERY_OR ){
+        pRoot = pExpr->pRight;
+        **ppOr = pRoot;
+        (*ppOr)++;
+      }
+      fts3EvalTokenCosts(pCsr, pRoot, pExpr->pRight, ppTC, ppOr, pRc);
+    }
+  }
+}
+
+/*
+** Determine the average document (row) size in pages. If successful,
+** write this value to *pnPage and return SQLITE_OK. Otherwise, return
+** an SQLite error code.
+**
+** The average document size in pages is calculated by first calculating 
+** determining the average size in bytes, B. If B is less than the amount
+** of data that will fit on a single leaf page of an intkey table in
+** this database, then the average docsize is 1. Otherwise, it is 1 plus
+** the number of overflow pages consumed by a record B bytes in size.
+*/
+static int fts3EvalAverageDocsize(Fts3Cursor *pCsr, int *pnPage){
+  if( pCsr->nRowAvg==0 ){
+    /* The average document size, which is required to calculate the cost
+    ** of each doclist, has not yet been determined. Read the required 
+    ** data from the %_stat table to calculate it.
+    **
+    ** Entry 0 of the %_stat table is a blob containing (nCol+1) FTS3 
+    ** varints, where nCol is the number of columns in the FTS3 table.
+    ** The first varint is the number of documents currently stored in
+    ** the table. The following nCol varints contain the total amount of
+    ** data stored in all rows of each column of the table, from left
+    ** to right.
+    */
+    int rc;
+    Fts3Table *p = (Fts3Table*)pCsr->base.pVtab;
+    sqlite3_stmt *pStmt;
+    sqlite3_int64 nDoc = 0;
+    sqlite3_int64 nByte = 0;
+    const char *pEnd;
+    const char *a;
+
+    rc = sqlite3Fts3SelectDoctotal(p, &pStmt);
+    if( rc!=SQLITE_OK ) return rc;
+    a = sqlite3_column_blob(pStmt, 0);
+    assert( a );
+
+    pEnd = &a[sqlite3_column_bytes(pStmt, 0)];
+    a += sqlite3Fts3GetVarint(a, &nDoc);
+    while( a<pEnd ){
+      a += sqlite3Fts3GetVarint(a, &nByte);
+    }
+    if( nDoc==0 || nByte==0 ){
+      sqlite3_reset(pStmt);
+      return FTS_CORRUPT_VTAB;
+    }
+
+    pCsr->nDoc = nDoc;
+    pCsr->nRowAvg = (int)(((nByte / nDoc) + p->nPgsz) / p->nPgsz);
+    assert( pCsr->nRowAvg>0 ); 
+    rc = sqlite3_reset(pStmt);
+    if( rc!=SQLITE_OK ) return rc;
+  }
+
+  *pnPage = pCsr->nRowAvg;
+  return SQLITE_OK;
+}
+
+/*
+** This function is called to select the tokens (if any) that will be 
+** deferred. The array aTC[] has already been populated when this is
+** called.
+**
+** This function is called once for each AND/NEAR cluster in the 
+** expression. Each invocation determines which tokens to defer within
+** the cluster with root node pRoot. See comments above the definition
+** of struct Fts3TokenAndCost for more details.
+**
+** If no error occurs, SQLITE_OK is returned and sqlite3Fts3DeferToken()
+** called on each token to defer. Otherwise, an SQLite error code is
+** returned.
+*/
+static int fts3EvalSelectDeferred(
+  Fts3Cursor *pCsr,               /* FTS Cursor handle */
+  Fts3Expr *pRoot,                /* Consider tokens with this root node */
+  Fts3TokenAndCost *aTC,          /* Array of expression tokens and costs */
+  int nTC                         /* Number of entries in aTC[] */
+){
+  Fts3Table *pTab = (Fts3Table *)pCsr->base.pVtab;
+  int nDocSize = 0;               /* Number of pages per doc loaded */
+  int rc = SQLITE_OK;             /* Return code */
+  int ii;                         /* Iterator variable for various purposes */
+  int nOvfl = 0;                  /* Total overflow pages used by doclists */
+  int nToken = 0;                 /* Total number of tokens in cluster */
+
+  int nMinEst = 0;                /* The minimum count for any phrase so far. */
+  int nLoad4 = 1;                 /* (Phrases that will be loaded)^4. */
+
+  /* Tokens are never deferred for FTS tables created using the content=xxx
+  ** option. The reason being that it is not guaranteed that the content
+  ** table actually contains the same data as the index. To prevent this from
+  ** causing any problems, the deferred token optimization is completely
+  ** disabled for content=xxx tables. */
+  if( pTab->zContentTbl ){
+    return SQLITE_OK;
+  }
+
+  /* Count the tokens in this AND/NEAR cluster. If none of the doclists
+  ** associated with the tokens spill onto overflow pages, or if there is
+  ** only 1 token, exit early. No tokens to defer in this case. */
+  for(ii=0; ii<nTC; ii++){
+    if( aTC[ii].pRoot==pRoot ){
+      nOvfl += aTC[ii].nOvfl;
+      nToken++;
+    }
+  }
+  if( nOvfl==0 || nToken<2 ) return SQLITE_OK;
+
+  /* Obtain the average docsize (in pages). */
+  rc = fts3EvalAverageDocsize(pCsr, &nDocSize);
+  assert( rc!=SQLITE_OK || nDocSize>0 );
+
+
+  /* Iterate through all tokens in this AND/NEAR cluster, in ascending order 
+  ** of the number of overflow pages that will be loaded by the pager layer 
+  ** to retrieve the entire doclist for the token from the full-text index.
+  ** Load the doclists for tokens that are either:
+  **
+  **   a. The cheapest token in the entire query (i.e. the one visited by the
+  **      first iteration of this loop), or
+  **
+  **   b. Part of a multi-token phrase.
+  **
+  ** After each token doclist is loaded, merge it with the others from the
+  ** same phrase and count the number of documents that the merged doclist
+  ** contains. Set variable "nMinEst" to the smallest number of documents in 
+  ** any phrase doclist for which 1 or more token doclists have been loaded.
+  ** Let nOther be the number of other phrases for which it is certain that
+  ** one or more tokens will not be deferred.
+  **
+  ** Then, for each token, defer it if loading the doclist would result in
+  ** loading N or more overflow pages into memory, where N is computed as:
+  **
+  **    (nMinEst + 4^nOther - 1) / (4^nOther)
+  */
+  for(ii=0; ii<nToken && rc==SQLITE_OK; ii++){
+    int iTC;                      /* Used to iterate through aTC[] array. */
+    Fts3TokenAndCost *pTC = 0;    /* Set to cheapest remaining token. */
+
+    /* Set pTC to point to the cheapest remaining token. */
+    for(iTC=0; iTC<nTC; iTC++){
+      if( aTC[iTC].pToken && aTC[iTC].pRoot==pRoot 
+       && (!pTC || aTC[iTC].nOvfl<pTC->nOvfl) 
+      ){
+        pTC = &aTC[iTC];
+      }
+    }
+    assert( pTC );
+
+    if( ii && pTC->nOvfl>=((nMinEst+(nLoad4/4)-1)/(nLoad4/4))*nDocSize ){
+      /* The number of overflow pages to load for this (and therefore all
+      ** subsequent) tokens is greater than the estimated number of pages 
+      ** that will be loaded if all subsequent tokens are deferred.
+      */
+      Fts3PhraseToken *pToken = pTC->pToken;
+      rc = sqlite3Fts3DeferToken(pCsr, pToken, pTC->iCol);
+      fts3SegReaderCursorFree(pToken->pSegcsr);
+      pToken->pSegcsr = 0;
+    }else{
+      /* Set nLoad4 to the value of (4^nOther) for the next iteration of the
+      ** for-loop. Except, limit the value to 2^24 to prevent it from 
+      ** overflowing the 32-bit integer it is stored in. */
+      if( ii<12 ) nLoad4 = nLoad4*4;
+
+      if( ii==0 || (pTC->pPhrase->nToken>1 && ii!=nToken-1) ){
+        /* Either this is the cheapest token in the entire query, or it is
+        ** part of a multi-token phrase. Either way, the entire doclist will
+        ** (eventually) be loaded into memory. It may as well be now. */
+        Fts3PhraseToken *pToken = pTC->pToken;
+        int nList = 0;
+        char *pList = 0;
+        rc = fts3TermSelect(pTab, pToken, pTC->iCol, &nList, &pList);
+        assert( rc==SQLITE_OK || pList==0 );
+        if( rc==SQLITE_OK ){
+          int nCount;
+          fts3EvalPhraseMergeToken(pTab, pTC->pPhrase, pTC->iToken,pList,nList);
+          nCount = fts3DoclistCountDocids(
+              pTC->pPhrase->doclist.aAll, pTC->pPhrase->doclist.nAll
+          );
+          if( ii==0 || nCount<nMinEst ) nMinEst = nCount;
+        }
+      }
+    }
+    pTC->pToken = 0;
+  }
+
+  return rc;
+}
+
+/*
+** This function is called from within the xFilter method. It initializes
+** the full-text query currently stored in pCsr->pExpr. To iterate through
+** the results of a query, the caller does:
+**
+**    fts3EvalStart(pCsr);
+**    while( 1 ){
+**      fts3EvalNext(pCsr);
+**      if( pCsr->bEof ) break;
+**      ... return row pCsr->iPrevId to the caller ...
+**    }
+*/
+static int fts3EvalStart(Fts3Cursor *pCsr){
+  Fts3Table *pTab = (Fts3Table *)pCsr->base.pVtab;
+  int rc = SQLITE_OK;
+  int nToken = 0;
+  int nOr = 0;
+
+  /* Allocate a MultiSegReader for each token in the expression. */
+  fts3EvalAllocateReaders(pCsr, pCsr->pExpr, &nToken, &nOr, &rc);
+
+  /* Determine which, if any, tokens in the expression should be deferred. */
+#ifndef SQLITE_DISABLE_FTS4_DEFERRED
+  if( rc==SQLITE_OK && nToken>1 && pTab->bFts4 ){
+    Fts3TokenAndCost *aTC;
+    Fts3Expr **apOr;
+    aTC = (Fts3TokenAndCost *)sqlite3_malloc(
+        sizeof(Fts3TokenAndCost) * nToken
+      + sizeof(Fts3Expr *) * nOr * 2
+    );
+    apOr = (Fts3Expr **)&aTC[nToken];
+
+    if( !aTC ){
+      rc = SQLITE_NOMEM;
+    }else{
+      int ii;
+      Fts3TokenAndCost *pTC = aTC;
+      Fts3Expr **ppOr = apOr;
+
+      fts3EvalTokenCosts(pCsr, 0, pCsr->pExpr, &pTC, &ppOr, &rc);
+      nToken = (int)(pTC-aTC);
+      nOr = (int)(ppOr-apOr);
+
+      if( rc==SQLITE_OK ){
+        rc = fts3EvalSelectDeferred(pCsr, 0, aTC, nToken);
+        for(ii=0; rc==SQLITE_OK && ii<nOr; ii++){
+          rc = fts3EvalSelectDeferred(pCsr, apOr[ii], aTC, nToken);
+        }
+      }
+
+      sqlite3_free(aTC);
+    }
+  }
+#endif
+
+  fts3EvalStartReaders(pCsr, pCsr->pExpr, &rc);
+  return rc;
+}
+
+/*
+** Invalidate the current position list for phrase pPhrase.
+*/
+static void fts3EvalInvalidatePoslist(Fts3Phrase *pPhrase){
+  if( pPhrase->doclist.bFreeList ){
+    sqlite3_free(pPhrase->doclist.pList);
+  }
+  pPhrase->doclist.pList = 0;
+  pPhrase->doclist.nList = 0;
+  pPhrase->doclist.bFreeList = 0;
+}
+
+/*
+** This function is called to edit the position list associated with
+** the phrase object passed as the fifth argument according to a NEAR
+** condition. For example:
+**
+**     abc NEAR/5 "def ghi"
+**
+** Parameter nNear is passed the NEAR distance of the expression (5 in
+** the example above). When this function is called, *paPoslist points to
+** the position list, and *pnToken is the number of phrase tokens in, the
+** phrase on the other side of the NEAR operator to pPhrase. For example,
+** if pPhrase refers to the "def ghi" phrase, then *paPoslist points to
+** the position list associated with phrase "abc".
+**
+** All positions in the pPhrase position list that are not sufficiently
+** close to a position in the *paPoslist position list are removed. If this
+** leaves 0 positions, zero is returned. Otherwise, non-zero.
+**
+** Before returning, *paPoslist is set to point to the position lsit 
+** associated with pPhrase. And *pnToken is set to the number of tokens in
+** pPhrase.
+*/
+static int fts3EvalNearTrim(
+  int nNear,                      /* NEAR distance. As in "NEAR/nNear". */
+  char *aTmp,                     /* Temporary space to use */
+  char **paPoslist,               /* IN/OUT: Position list */
+  int *pnToken,                   /* IN/OUT: Tokens in phrase of *paPoslist */
+  Fts3Phrase *pPhrase             /* The phrase object to trim the doclist of */
+){
+  int nParam1 = nNear + pPhrase->nToken;
+  int nParam2 = nNear + *pnToken;
+  int nNew;
+  char *p2; 
+  char *pOut; 
+  int res;
+
+  assert( pPhrase->doclist.pList );
+
+  p2 = pOut = pPhrase->doclist.pList;
+  res = fts3PoslistNearMerge(
+    &pOut, aTmp, nParam1, nParam2, paPoslist, &p2
+  );
+  if( res ){
+    nNew = (int)(pOut - pPhrase->doclist.pList) - 1;
+    assert( pPhrase->doclist.pList[nNew]=='\0' );
+    assert( nNew<=pPhrase->doclist.nList && nNew>0 );
+    memset(&pPhrase->doclist.pList[nNew], 0, pPhrase->doclist.nList - nNew);
+    pPhrase->doclist.nList = nNew;
+    *paPoslist = pPhrase->doclist.pList;
+    *pnToken = pPhrase->nToken;
+  }
+
+  return res;
+}
+
+/*
+** This function is a no-op if *pRc is other than SQLITE_OK when it is called.
+** Otherwise, it advances the expression passed as the second argument to
+** point to the next matching row in the database. Expressions iterate through
+** matching rows in docid order. Ascending order if Fts3Cursor.bDesc is zero,
+** or descending if it is non-zero.
+**
+** If an error occurs, *pRc is set to an SQLite error code. Otherwise, if
+** successful, the following variables in pExpr are set:
+**
+**   Fts3Expr.bEof                (non-zero if EOF - there is no next row)
+**   Fts3Expr.iDocid              (valid if bEof==0. The docid of the next row)
+**
+** If the expression is of type FTSQUERY_PHRASE, and the expression is not
+** at EOF, then the following variables are populated with the position list
+** for the phrase for the visited row:
+**
+**   FTs3Expr.pPhrase->doclist.nList        (length of pList in bytes)
+**   FTs3Expr.pPhrase->doclist.pList        (pointer to position list)
+**
+** It says above that this function advances the expression to the next
+** matching row. This is usually true, but there are the following exceptions:
+**
+**   1. Deferred tokens are not taken into account. If a phrase consists
+**      entirely of deferred tokens, it is assumed to match every row in
+**      the db. In this case the position-list is not populated at all. 
+**
+**      Or, if a phrase contains one or more deferred tokens and one or
+**      more non-deferred tokens, then the expression is advanced to the 
+**      next possible match, considering only non-deferred tokens. In other
+**      words, if the phrase is "A B C", and "B" is deferred, the expression
+**      is advanced to the next row that contains an instance of "A * C", 
+**      where "*" may match any single token. The position list in this case
+**      is populated as for "A * C" before returning.
+**
+**   2. NEAR is treated as AND. If the expression is "x NEAR y", it is 
+**      advanced to point to the next row that matches "x AND y".
+** 
+** See fts3EvalTestDeferredAndNear() for details on testing if a row is
+** really a match, taking into account deferred tokens and NEAR operators.
+*/
+static void fts3EvalNextRow(
+  Fts3Cursor *pCsr,               /* FTS Cursor handle */
+  Fts3Expr *pExpr,                /* Expr. to advance to next matching row */
+  int *pRc                        /* IN/OUT: Error code */
+){
+  if( *pRc==SQLITE_OK ){
+    int bDescDoclist = pCsr->bDesc;         /* Used by DOCID_CMP() macro */
+    assert( pExpr->bEof==0 );
+    pExpr->bStart = 1;
+
+    switch( pExpr->eType ){
+      case FTSQUERY_NEAR:
+      case FTSQUERY_AND: {
+        Fts3Expr *pLeft = pExpr->pLeft;
+        Fts3Expr *pRight = pExpr->pRight;
+        assert( !pLeft->bDeferred || !pRight->bDeferred );
+
+        if( pLeft->bDeferred ){
+          /* LHS is entirely deferred. So we assume it matches every row.
+          ** Advance the RHS iterator to find the next row visited. */
+          fts3EvalNextRow(pCsr, pRight, pRc);
+          pExpr->iDocid = pRight->iDocid;
+          pExpr->bEof = pRight->bEof;
+        }else if( pRight->bDeferred ){
+          /* RHS is entirely deferred. So we assume it matches every row.
+          ** Advance the LHS iterator to find the next row visited. */
+          fts3EvalNextRow(pCsr, pLeft, pRc);
+          pExpr->iDocid = pLeft->iDocid;
+          pExpr->bEof = pLeft->bEof;
+        }else{
+          /* Neither the RHS or LHS are deferred. */
+          fts3EvalNextRow(pCsr, pLeft, pRc);
+          fts3EvalNextRow(pCsr, pRight, pRc);
+          while( !pLeft->bEof && !pRight->bEof && *pRc==SQLITE_OK ){
+            sqlite3_int64 iDiff = DOCID_CMP(pLeft->iDocid, pRight->iDocid);
+            if( iDiff==0 ) break;
+            if( iDiff<0 ){
+              fts3EvalNextRow(pCsr, pLeft, pRc);
+            }else{
+              fts3EvalNextRow(pCsr, pRight, pRc);
+            }
+          }
+          pExpr->iDocid = pLeft->iDocid;
+          pExpr->bEof = (pLeft->bEof || pRight->bEof);
+        }
+        break;
+      }
+  
+      case FTSQUERY_OR: {
+        Fts3Expr *pLeft = pExpr->pLeft;
+        Fts3Expr *pRight = pExpr->pRight;
+        sqlite3_int64 iCmp = DOCID_CMP(pLeft->iDocid, pRight->iDocid);
+
+        assert( pLeft->bStart || pLeft->iDocid==pRight->iDocid );
+        assert( pRight->bStart || pLeft->iDocid==pRight->iDocid );
+
+        if( pRight->bEof || (pLeft->bEof==0 && iCmp<0) ){
+          fts3EvalNextRow(pCsr, pLeft, pRc);
+        }else if( pLeft->bEof || (pRight->bEof==0 && iCmp>0) ){
+          fts3EvalNextRow(pCsr, pRight, pRc);
+        }else{
+          fts3EvalNextRow(pCsr, pLeft, pRc);
+          fts3EvalNextRow(pCsr, pRight, pRc);
+        }
+
+        pExpr->bEof = (pLeft->bEof && pRight->bEof);
+        iCmp = DOCID_CMP(pLeft->iDocid, pRight->iDocid);
+        if( pRight->bEof || (pLeft->bEof==0 &&  iCmp<0) ){
+          pExpr->iDocid = pLeft->iDocid;
+        }else{
+          pExpr->iDocid = pRight->iDocid;
+        }
+
+        break;
+      }
+
+      case FTSQUERY_NOT: {
+        Fts3Expr *pLeft = pExpr->pLeft;
+        Fts3Expr *pRight = pExpr->pRight;
+
+        if( pRight->bStart==0 ){
+          fts3EvalNextRow(pCsr, pRight, pRc);
+          assert( *pRc!=SQLITE_OK || pRight->bStart );
+        }
+
+        fts3EvalNextRow(pCsr, pLeft, pRc);
+        if( pLeft->bEof==0 ){
+          while( !*pRc 
+              && !pRight->bEof 
+              && DOCID_CMP(pLeft->iDocid, pRight->iDocid)>0 
+          ){
+            fts3EvalNextRow(pCsr, pRight, pRc);
+          }
+        }
+        pExpr->iDocid = pLeft->iDocid;
+        pExpr->bEof = pLeft->bEof;
+        break;
+      }
+
+      default: {
+        Fts3Phrase *pPhrase = pExpr->pPhrase;
+        fts3EvalInvalidatePoslist(pPhrase);
+        *pRc = fts3EvalPhraseNext(pCsr, pPhrase, &pExpr->bEof);
+        pExpr->iDocid = pPhrase->doclist.iDocid;
+        break;
+      }
+    }
+  }
+}
+
+/*
+** If *pRc is not SQLITE_OK, or if pExpr is not the root node of a NEAR
+** cluster, then this function returns 1 immediately.
+**
+** Otherwise, it checks if the current row really does match the NEAR 
+** expression, using the data currently stored in the position lists 
+** (Fts3Expr->pPhrase.doclist.pList/nList) for each phrase in the expression. 
+**
+** If the current row is a match, the position list associated with each
+** phrase in the NEAR expression is edited in place to contain only those
+** phrase instances sufficiently close to their peers to satisfy all NEAR
+** constraints. In this case it returns 1. If the NEAR expression does not 
+** match the current row, 0 is returned. The position lists may or may not
+** be edited if 0 is returned.
+*/
+static int fts3EvalNearTest(Fts3Expr *pExpr, int *pRc){
+  int res = 1;
+
+  /* The following block runs if pExpr is the root of a NEAR query.
+  ** For example, the query:
+  **
+  **         "w" NEAR "x" NEAR "y" NEAR "z"
+  **
+  ** which is represented in tree form as:
+  **
+  **                               |
+  **                          +--NEAR--+      <-- root of NEAR query
+  **                          |        |
+  **                     +--NEAR--+   "z"
+  **                     |        |
+  **                +--NEAR--+   "y"
+  **                |        |
+  **               "w"      "x"
+  **
+  ** The right-hand child of a NEAR node is always a phrase. The 
+  ** left-hand child may be either a phrase or a NEAR node. There are
+  ** no exceptions to this - it's the way the parser in fts3_expr.c works.
+  */
+  if( *pRc==SQLITE_OK 
+   && pExpr->eType==FTSQUERY_NEAR 
+   && pExpr->bEof==0
+   && (pExpr->pParent==0 || pExpr->pParent->eType!=FTSQUERY_NEAR)
+  ){
+    Fts3Expr *p; 
+    int nTmp = 0;                 /* Bytes of temp space */
+    char *aTmp;                   /* Temp space for PoslistNearMerge() */
+
+    /* Allocate temporary working space. */
+    for(p=pExpr; p->pLeft; p=p->pLeft){
+      nTmp += p->pRight->pPhrase->doclist.nList;
+    }
+    nTmp += p->pPhrase->doclist.nList;
+    if( nTmp==0 ){
+      res = 0;
+    }else{
+      aTmp = sqlite3_malloc(nTmp*2);
+      if( !aTmp ){
+        *pRc = SQLITE_NOMEM;
+        res = 0;
+      }else{
+        char *aPoslist = p->pPhrase->doclist.pList;
+        int nToken = p->pPhrase->nToken;
+
+        for(p=p->pParent;res && p && p->eType==FTSQUERY_NEAR; p=p->pParent){
+          Fts3Phrase *pPhrase = p->pRight->pPhrase;
+          int nNear = p->nNear;
+          res = fts3EvalNearTrim(nNear, aTmp, &aPoslist, &nToken, pPhrase);
+        }
+
+        aPoslist = pExpr->pRight->pPhrase->doclist.pList;
+        nToken = pExpr->pRight->pPhrase->nToken;
+        for(p=pExpr->pLeft; p && res; p=p->pLeft){
+          int nNear;
+          Fts3Phrase *pPhrase;
+          assert( p->pParent && p->pParent->pLeft==p );
+          nNear = p->pParent->nNear;
+          pPhrase = (
+              p->eType==FTSQUERY_NEAR ? p->pRight->pPhrase : p->pPhrase
+              );
+          res = fts3EvalNearTrim(nNear, aTmp, &aPoslist, &nToken, pPhrase);
+        }
+      }
+
+      sqlite3_free(aTmp);
+    }
+  }
+
+  return res;
+}
+
+/*
+** This function is a helper function for fts3EvalTestDeferredAndNear().
+** Assuming no error occurs or has occurred, It returns non-zero if the
+** expression passed as the second argument matches the row that pCsr 
+** currently points to, or zero if it does not.
+**
+** If *pRc is not SQLITE_OK when this function is called, it is a no-op.
+** If an error occurs during execution of this function, *pRc is set to 
+** the appropriate SQLite error code. In this case the returned value is 
+** undefined.
+*/
+static int fts3EvalTestExpr(
+  Fts3Cursor *pCsr,               /* FTS cursor handle */
+  Fts3Expr *pExpr,                /* Expr to test. May or may not be root. */
+  int *pRc                        /* IN/OUT: Error code */
+){
+  int bHit = 1;                   /* Return value */
+  if( *pRc==SQLITE_OK ){
+    switch( pExpr->eType ){
+      case FTSQUERY_NEAR:
+      case FTSQUERY_AND:
+        bHit = (
+            fts3EvalTestExpr(pCsr, pExpr->pLeft, pRc)
+         && fts3EvalTestExpr(pCsr, pExpr->pRight, pRc)
+         && fts3EvalNearTest(pExpr, pRc)
+        );
+
+        /* If the NEAR expression does not match any rows, zero the doclist for 
+        ** all phrases involved in the NEAR. This is because the snippet(),
+        ** offsets() and matchinfo() functions are not supposed to recognize 
+        ** any instances of phrases that are part of unmatched NEAR queries. 
+        ** For example if this expression:
+        **
+        **    ... MATCH 'a OR (b NEAR c)'
+        **
+        ** is matched against a row containing:
+        **
+        **        'a b d e'
+        **
+        ** then any snippet() should ony highlight the "a" term, not the "b"
+        ** (as "b" is part of a non-matching NEAR clause).
+        */
+        if( bHit==0 
+         && pExpr->eType==FTSQUERY_NEAR 
+         && (pExpr->pParent==0 || pExpr->pParent->eType!=FTSQUERY_NEAR)
+        ){
+          Fts3Expr *p;
+          for(p=pExpr; p->pPhrase==0; p=p->pLeft){
+            if( p->pRight->iDocid==pCsr->iPrevId ){
+              fts3EvalInvalidatePoslist(p->pRight->pPhrase);
+            }
+          }
+          if( p->iDocid==pCsr->iPrevId ){
+            fts3EvalInvalidatePoslist(p->pPhrase);
+          }
+        }
+
+        break;
+
+      case FTSQUERY_OR: {
+        int bHit1 = fts3EvalTestExpr(pCsr, pExpr->pLeft, pRc);
+        int bHit2 = fts3EvalTestExpr(pCsr, pExpr->pRight, pRc);
+        bHit = bHit1 || bHit2;
+        break;
+      }
+
+      case FTSQUERY_NOT:
+        bHit = (
+            fts3EvalTestExpr(pCsr, pExpr->pLeft, pRc)
+         && !fts3EvalTestExpr(pCsr, pExpr->pRight, pRc)
+        );
+        break;
+
+      default: {
+#ifndef SQLITE_DISABLE_FTS4_DEFERRED
+        if( pCsr->pDeferred 
+         && (pExpr->iDocid==pCsr->iPrevId || pExpr->bDeferred)
+        ){
+          Fts3Phrase *pPhrase = pExpr->pPhrase;
+          assert( pExpr->bDeferred || pPhrase->doclist.bFreeList==0 );
+          if( pExpr->bDeferred ){
+            fts3EvalInvalidatePoslist(pPhrase);
+          }
+          *pRc = fts3EvalDeferredPhrase(pCsr, pPhrase);
+          bHit = (pPhrase->doclist.pList!=0);
+          pExpr->iDocid = pCsr->iPrevId;
+        }else
+#endif
+        {
+          bHit = (pExpr->bEof==0 && pExpr->iDocid==pCsr->iPrevId);
+        }
+        break;
+      }
+    }
+  }
+  return bHit;
+}
+
+/*
+** This function is called as the second part of each xNext operation when
+** iterating through the results of a full-text query. At this point the
+** cursor points to a row that matches the query expression, with the
+** following caveats:
+**
+**   * Up until this point, "NEAR" operators in the expression have been
+**     treated as "AND".
+**
+**   * Deferred tokens have not yet been considered.
+**
+** If *pRc is not SQLITE_OK when this function is called, it immediately
+** returns 0. Otherwise, it tests whether or not after considering NEAR
+** operators and deferred tokens the current row is still a match for the
+** expression. It returns 1 if both of the following are true:
+**
+**   1. *pRc is SQLITE_OK when this function returns, and
+**
+**   2. After scanning the current FTS table row for the deferred tokens,
+**      it is determined that the row does *not* match the query.
+**
+** Or, if no error occurs and it seems the current row does match the FTS
+** query, return 0.
+*/
+static int fts3EvalTestDeferredAndNear(Fts3Cursor *pCsr, int *pRc){
+  int rc = *pRc;
+  int bMiss = 0;
+  if( rc==SQLITE_OK ){
+
+    /* If there are one or more deferred tokens, load the current row into
+    ** memory and scan it to determine the position list for each deferred
+    ** token. Then, see if this row is really a match, considering deferred
+    ** tokens and NEAR operators (neither of which were taken into account
+    ** earlier, by fts3EvalNextRow()). 
+    */
+    if( pCsr->pDeferred ){
+      rc = fts3CursorSeek(0, pCsr);
+      if( rc==SQLITE_OK ){
+        rc = sqlite3Fts3CacheDeferredDoclists(pCsr);
+      }
+    }
+    bMiss = (0==fts3EvalTestExpr(pCsr, pCsr->pExpr, &rc));
+
+    /* Free the position-lists accumulated for each deferred token above. */
+    sqlite3Fts3FreeDeferredDoclists(pCsr);
+    *pRc = rc;
+  }
+  return (rc==SQLITE_OK && bMiss);
+}
+
+/*
+** Advance to the next document that matches the FTS expression in
+** Fts3Cursor.pExpr.
+*/
+static int fts3EvalNext(Fts3Cursor *pCsr){
+  int rc = SQLITE_OK;             /* Return Code */
+  Fts3Expr *pExpr = pCsr->pExpr;
+  assert( pCsr->isEof==0 );
+  if( pExpr==0 ){
+    pCsr->isEof = 1;
+  }else{
+    do {
+      if( pCsr->isRequireSeek==0 ){
+        sqlite3_reset(pCsr->pStmt);
+      }
+      assert( sqlite3_data_count(pCsr->pStmt)==0 );
+      fts3EvalNextRow(pCsr, pExpr, &rc);
+      pCsr->isEof = pExpr->bEof;
+      pCsr->isRequireSeek = 1;
+      pCsr->isMatchinfoNeeded = 1;
+      pCsr->iPrevId = pExpr->iDocid;
+    }while( pCsr->isEof==0 && fts3EvalTestDeferredAndNear(pCsr, &rc) );
+  }
+
+  /* Check if the cursor is past the end of the docid range specified
+  ** by Fts3Cursor.iMinDocid/iMaxDocid. If so, set the EOF flag.  */
+  if( rc==SQLITE_OK && (
+        (pCsr->bDesc==0 && pCsr->iPrevId>pCsr->iMaxDocid)
+     || (pCsr->bDesc!=0 && pCsr->iPrevId<pCsr->iMinDocid)
+  )){
+    pCsr->isEof = 1;
+  }
+
+  return rc;
+}
+
+/*
+** Restart interation for expression pExpr so that the next call to
+** fts3EvalNext() visits the first row. Do not allow incremental 
+** loading or merging of phrase doclists for this iteration.
+**
+** If *pRc is other than SQLITE_OK when this function is called, it is
+** a no-op. If an error occurs within this function, *pRc is set to an
+** SQLite error code before returning.
+*/
+static void fts3EvalRestart(
+  Fts3Cursor *pCsr,
+  Fts3Expr *pExpr,
+  int *pRc
+){
+  if( pExpr && *pRc==SQLITE_OK ){
+    Fts3Phrase *pPhrase = pExpr->pPhrase;
+
+    if( pPhrase ){
+      fts3EvalInvalidatePoslist(pPhrase);
+      if( pPhrase->bIncr ){
+        int i;
+        for(i=0; i<pPhrase->nToken; i++){
+          Fts3PhraseToken *pToken = &pPhrase->aToken[i];
+          assert( pToken->pDeferred==0 );
+          if( pToken->pSegcsr ){
+            sqlite3Fts3MsrIncrRestart(pToken->pSegcsr);
+          }
+        }
+        *pRc = fts3EvalPhraseStart(pCsr, 0, pPhrase);
+      }
+      pPhrase->doclist.pNextDocid = 0;
+      pPhrase->doclist.iDocid = 0;
+    }
+
+    pExpr->iDocid = 0;
+    pExpr->bEof = 0;
+    pExpr->bStart = 0;
+
+    fts3EvalRestart(pCsr, pExpr->pLeft, pRc);
+    fts3EvalRestart(pCsr, pExpr->pRight, pRc);
+  }
+}
+
+/*
+** After allocating the Fts3Expr.aMI[] array for each phrase in the 
+** expression rooted at pExpr, the cursor iterates through all rows matched
+** by pExpr, calling this function for each row. This function increments
+** the values in Fts3Expr.aMI[] according to the position-list currently
+** found in Fts3Expr.pPhrase->doclist.pList for each of the phrase 
+** expression nodes.
+*/
+static void fts3EvalUpdateCounts(Fts3Expr *pExpr){
+  if( pExpr ){
+    Fts3Phrase *pPhrase = pExpr->pPhrase;
+    if( pPhrase && pPhrase->doclist.pList ){
+      int iCol = 0;
+      char *p = pPhrase->doclist.pList;
+
+      assert( *p );
+      while( 1 ){
+        u8 c = 0;
+        int iCnt = 0;
+        while( 0xFE & (*p | c) ){
+          if( (c&0x80)==0 ) iCnt++;
+          c = *p++ & 0x80;
+        }
+
+        /* aMI[iCol*3 + 1] = Number of occurrences
+        ** aMI[iCol*3 + 2] = Number of rows containing at least one instance
+        */
+        pExpr->aMI[iCol*3 + 1] += iCnt;
+        pExpr->aMI[iCol*3 + 2] += (iCnt>0);
+        if( *p==0x00 ) break;
+        p++;
+        p += fts3GetVarint32(p, &iCol);
+      }
+    }
+
+    fts3EvalUpdateCounts(pExpr->pLeft);
+    fts3EvalUpdateCounts(pExpr->pRight);
+  }
+}
+
+/*
+** Expression pExpr must be of type FTSQUERY_PHRASE.
+**
+** If it is not already allocated and populated, this function allocates and
+** populates the Fts3Expr.aMI[] array for expression pExpr. If pExpr is part
+** of a NEAR expression, then it also allocates and populates the same array
+** for all other phrases that are part of the NEAR expression.
+**
+** SQLITE_OK is returned if the aMI[] array is successfully allocated and
+** populated. Otherwise, if an error occurs, an SQLite error code is returned.
+*/
+static int fts3EvalGatherStats(
+  Fts3Cursor *pCsr,               /* Cursor object */
+  Fts3Expr *pExpr                 /* FTSQUERY_PHRASE expression */
+){
+  int rc = SQLITE_OK;             /* Return code */
+
+  assert( pExpr->eType==FTSQUERY_PHRASE );
+  if( pExpr->aMI==0 ){
+    Fts3Table *pTab = (Fts3Table *)pCsr->base.pVtab;
+    Fts3Expr *pRoot;                /* Root of NEAR expression */
+    Fts3Expr *p;                    /* Iterator used for several purposes */
+
+    sqlite3_int64 iPrevId = pCsr->iPrevId;
+    sqlite3_int64 iDocid;
+    u8 bEof;
+
+    /* Find the root of the NEAR expression */
+    pRoot = pExpr;
+    while( pRoot->pParent && pRoot->pParent->eType==FTSQUERY_NEAR ){
+      pRoot = pRoot->pParent;
+    }
+    iDocid = pRoot->iDocid;
+    bEof = pRoot->bEof;
+    assert( pRoot->bStart );
+
+    /* Allocate space for the aMSI[] array of each FTSQUERY_PHRASE node */
+    for(p=pRoot; p; p=p->pLeft){
+      Fts3Expr *pE = (p->eType==FTSQUERY_PHRASE?p:p->pRight);
+      assert( pE->aMI==0 );
+      pE->aMI = (u32 *)sqlite3_malloc(pTab->nColumn * 3 * sizeof(u32));
+      if( !pE->aMI ) return SQLITE_NOMEM;
+      memset(pE->aMI, 0, pTab->nColumn * 3 * sizeof(u32));
+    }
+
+    fts3EvalRestart(pCsr, pRoot, &rc);
+
+    while( pCsr->isEof==0 && rc==SQLITE_OK ){
+
+      do {
+        /* Ensure the %_content statement is reset. */
+        if( pCsr->isRequireSeek==0 ) sqlite3_reset(pCsr->pStmt);
+        assert( sqlite3_data_count(pCsr->pStmt)==0 );
+
+        /* Advance to the next document */
+        fts3EvalNextRow(pCsr, pRoot, &rc);
+        pCsr->isEof = pRoot->bEof;
+        pCsr->isRequireSeek = 1;
+        pCsr->isMatchinfoNeeded = 1;
+        pCsr->iPrevId = pRoot->iDocid;
+      }while( pCsr->isEof==0 
+           && pRoot->eType==FTSQUERY_NEAR 
+           && fts3EvalTestDeferredAndNear(pCsr, &rc) 
+      );
+
+      if( rc==SQLITE_OK && pCsr->isEof==0 ){
+        fts3EvalUpdateCounts(pRoot);
+      }
+    }
+
+    pCsr->isEof = 0;
+    pCsr->iPrevId = iPrevId;
+
+    if( bEof ){
+      pRoot->bEof = bEof;
+    }else{
+      /* Caution: pRoot may iterate through docids in ascending or descending
+      ** order. For this reason, even though it seems more defensive, the 
+      ** do loop can not be written:
+      **
+      **   do {...} while( pRoot->iDocid<iDocid && rc==SQLITE_OK );
+      */
+      fts3EvalRestart(pCsr, pRoot, &rc);
+      do {
+        fts3EvalNextRow(pCsr, pRoot, &rc);
+        assert( pRoot->bEof==0 );
+      }while( pRoot->iDocid!=iDocid && rc==SQLITE_OK );
+      fts3EvalTestDeferredAndNear(pCsr, &rc);
+    }
+  }
+  return rc;
+}
+
+/*
+** This function is used by the matchinfo() module to query a phrase 
+** expression node for the following information:
+**
+**   1. The total number of occurrences of the phrase in each column of 
+**      the FTS table (considering all rows), and
+**
+**   2. For each column, the number of rows in the table for which the
+**      column contains at least one instance of the phrase.
+**
+** If no error occurs, SQLITE_OK is returned and the values for each column
+** written into the array aiOut as follows:
+**
+**   aiOut[iCol*3 + 1] = Number of occurrences
+**   aiOut[iCol*3 + 2] = Number of rows containing at least one instance
+**
+** Caveats:
+**
+**   * If a phrase consists entirely of deferred tokens, then all output 
+**     values are set to the number of documents in the table. In other
+**     words we assume that very common tokens occur exactly once in each 
+**     column of each row of the table.
+**
+**   * If a phrase contains some deferred tokens (and some non-deferred 
+**     tokens), count the potential occurrence identified by considering
+**     the non-deferred tokens instead of actual phrase occurrences.
+**
+**   * If the phrase is part of a NEAR expression, then only phrase instances
+**     that meet the NEAR constraint are included in the counts.
+*/
+int sqlite3Fts3EvalPhraseStats(
+  Fts3Cursor *pCsr,               /* FTS cursor handle */
+  Fts3Expr *pExpr,                /* Phrase expression */
+  u32 *aiOut                      /* Array to write results into (see above) */
+){
+  Fts3Table *pTab = (Fts3Table *)pCsr->base.pVtab;
+  int rc = SQLITE_OK;
+  int iCol;
+
+  if( pExpr->bDeferred && pExpr->pParent->eType!=FTSQUERY_NEAR ){
+    assert( pCsr->nDoc>0 );
+    for(iCol=0; iCol<pTab->nColumn; iCol++){
+      aiOut[iCol*3 + 1] = (u32)pCsr->nDoc;
+      aiOut[iCol*3 + 2] = (u32)pCsr->nDoc;
+    }
+  }else{
+    rc = fts3EvalGatherStats(pCsr, pExpr);
+    if( rc==SQLITE_OK ){
+      assert( pExpr->aMI );
+      for(iCol=0; iCol<pTab->nColumn; iCol++){
+        aiOut[iCol*3 + 1] = pExpr->aMI[iCol*3 + 1];
+        aiOut[iCol*3 + 2] = pExpr->aMI[iCol*3 + 2];
+      }
+    }
+  }
+
+  return rc;
+}
+
+/*
+** The expression pExpr passed as the second argument to this function
+** must be of type FTSQUERY_PHRASE. 
+**
+** The returned value is either NULL or a pointer to a buffer containing
+** a position-list indicating the occurrences of the phrase in column iCol
+** of the current row. 
+**
+** More specifically, the returned buffer contains 1 varint for each 
+** occurrence of the phrase in the column, stored using the normal (delta+2) 
+** compression and is terminated by either an 0x01 or 0x00 byte. For example,
+** if the requested column contains "a b X c d X X" and the position-list
+** for 'X' is requested, the buffer returned may contain:
+**
+**     0x04 0x05 0x03 0x01   or   0x04 0x05 0x03 0x00
+**
+** This function works regardless of whether or not the phrase is deferred,
+** incremental, or neither.
+*/
+int sqlite3Fts3EvalPhrasePoslist(
+  Fts3Cursor *pCsr,               /* FTS3 cursor object */
+  Fts3Expr *pExpr,                /* Phrase to return doclist for */
+  int iCol,                       /* Column to return position list for */
+  char **ppOut                    /* OUT: Pointer to position list */
+){
+  Fts3Phrase *pPhrase = pExpr->pPhrase;
+  Fts3Table *pTab = (Fts3Table *)pCsr->base.pVtab;
+  char *pIter;
+  int iThis;
+  sqlite3_int64 iDocid;
+
+  /* If this phrase is applies specifically to some column other than 
+  ** column iCol, return a NULL pointer.  */
+  *ppOut = 0;
+  assert( iCol>=0 && iCol<pTab->nColumn );
+  if( (pPhrase->iColumn<pTab->nColumn && pPhrase->iColumn!=iCol) ){
+    return SQLITE_OK;
+  }
+
+  iDocid = pExpr->iDocid;
+  pIter = pPhrase->doclist.pList;
+  if( iDocid!=pCsr->iPrevId || pExpr->bEof ){
+    int bDescDoclist = pTab->bDescIdx;      /* For DOCID_CMP macro */
+    int iMul;                     /* +1 if csr dir matches index dir, else -1 */
+    int bOr = 0;
+    u8 bEof = 0;
+    u8 bTreeEof = 0;
+    Fts3Expr *p;                  /* Used to iterate from pExpr to root */
+    Fts3Expr *pNear;              /* Most senior NEAR ancestor (or pExpr) */
+
+    /* Check if this phrase descends from an OR expression node. If not, 
+    ** return NULL. Otherwise, the entry that corresponds to docid 
+    ** pCsr->iPrevId may lie earlier in the doclist buffer. Or, if the
+    ** tree that the node is part of has been marked as EOF, but the node
+    ** itself is not EOF, then it may point to an earlier entry. */
+    pNear = pExpr;
+    for(p=pExpr->pParent; p; p=p->pParent){
+      if( p->eType==FTSQUERY_OR ) bOr = 1;
+      if( p->eType==FTSQUERY_NEAR ) pNear = p;
+      if( p->bEof ) bTreeEof = 1;
+    }
+    if( bOr==0 ) return SQLITE_OK;
+
+    /* This is the descendent of an OR node. In this case we cannot use
+    ** an incremental phrase. Load the entire doclist for the phrase
+    ** into memory in this case.  */
+    if( pPhrase->bIncr ){
+      int rc = SQLITE_OK;
+      int bEofSave = pExpr->bEof;
+      fts3EvalRestart(pCsr, pExpr, &rc);
+      while( rc==SQLITE_OK && !pExpr->bEof ){
+        fts3EvalNextRow(pCsr, pExpr, &rc);
+        if( bEofSave==0 && pExpr->iDocid==iDocid ) break;
+      }
+      pIter = pPhrase->doclist.pList;
+      assert( rc!=SQLITE_OK || pPhrase->bIncr==0 );
+      if( rc!=SQLITE_OK ) return rc;
+    }
+    
+    iMul = ((pCsr->bDesc==bDescDoclist) ? 1 : -1);
+    while( bTreeEof==1 
+        && pNear->bEof==0
+        && (DOCID_CMP(pNear->iDocid, pCsr->iPrevId) * iMul)<0
+    ){
+      int rc = SQLITE_OK;
+      fts3EvalNextRow(pCsr, pExpr, &rc);
+      if( rc!=SQLITE_OK ) return rc;
+      iDocid = pExpr->iDocid;
+      pIter = pPhrase->doclist.pList;
+    }
+
+    bEof = (pPhrase->doclist.nAll==0);
+    assert( bDescDoclist==0 || bDescDoclist==1 );
+    assert( pCsr->bDesc==0 || pCsr->bDesc==1 );
+
+    if( bEof==0 ){
+      if( pCsr->bDesc==bDescDoclist ){
+        int dummy;
+        if( pNear->bEof ){
+          /* This expression is already at EOF. So position it to point to the
+          ** last entry in the doclist at pPhrase->doclist.aAll[]. Variable
+          ** iDocid is already set for this entry, so all that is required is
+          ** to set pIter to point to the first byte of the last position-list
+          ** in the doclist. 
+          **
+          ** It would also be correct to set pIter and iDocid to zero. In
+          ** this case, the first call to sqltie3Fts4DoclistPrev() below
+          ** would also move the iterator to point to the last entry in the 
+          ** doclist. However, this is expensive, as to do so it has to 
+          ** iterate through the entire doclist from start to finish (since
+          ** it does not know the docid for the last entry).  */
+          pIter = &pPhrase->doclist.aAll[pPhrase->doclist.nAll-1];
+          fts3ReversePoslist(pPhrase->doclist.aAll, &pIter);
+        }
+        while( (pIter==0 || DOCID_CMP(iDocid, pCsr->iPrevId)>0 ) && bEof==0 ){
+          sqlite3Fts3DoclistPrev(
+              bDescDoclist, pPhrase->doclist.aAll, pPhrase->doclist.nAll, 
+              &pIter, &iDocid, &dummy, &bEof
+          );
+        }
+      }else{
+        if( pNear->bEof ){
+          pIter = 0;
+          iDocid = 0;
+        }
+        while( (pIter==0 || DOCID_CMP(iDocid, pCsr->iPrevId)<0 ) && bEof==0 ){
+          sqlite3Fts3DoclistNext(
+              bDescDoclist, pPhrase->doclist.aAll, pPhrase->doclist.nAll, 
+              &pIter, &iDocid, &bEof
+          );
+        }
+      }
+    }
+
+    if( bEof || iDocid!=pCsr->iPrevId ) pIter = 0;
+  }
+  if( pIter==0 ) return SQLITE_OK;
+
+  if( *pIter==0x01 ){
+    pIter++;
+    pIter += fts3GetVarint32(pIter, &iThis);
+  }else{
+    iThis = 0;
+  }
+  while( iThis<iCol ){
+    fts3ColumnlistCopy(0, &pIter);
+    if( *pIter==0x00 ) return 0;
+    pIter++;
+    pIter += fts3GetVarint32(pIter, &iThis);
+  }
+
+  *ppOut = ((iCol==iThis)?pIter:0);
+  return SQLITE_OK;
+}
+
+/*
+** Free all components of the Fts3Phrase structure that were allocated by
+** the eval module. Specifically, this means to free:
+**
+**   * the contents of pPhrase->doclist, and
+**   * any Fts3MultiSegReader objects held by phrase tokens.
+*/
+void sqlite3Fts3EvalPhraseCleanup(Fts3Phrase *pPhrase){
+  if( pPhrase ){
+    int i;
+    sqlite3_free(pPhrase->doclist.aAll);
+    fts3EvalInvalidatePoslist(pPhrase);
+    memset(&pPhrase->doclist, 0, sizeof(Fts3Doclist));
+    for(i=0; i<pPhrase->nToken; i++){
+      fts3SegReaderCursorFree(pPhrase->aToken[i].pSegcsr);
+      pPhrase->aToken[i].pSegcsr = 0;
+    }
+  }
+}
+
+
+/*
+** Return SQLITE_CORRUPT_VTAB.
+*/
+#ifdef SQLITE_DEBUG
+int sqlite3Fts3Corrupt(){
+  return SQLITE_CORRUPT_VTAB;
+}
+#endif
+
 #if !SQLITE_CORE
-int sqlite3_extension_init(
+/*
+** Initialize API pointer table, if required.
+*/
+#ifdef _WIN32
+__declspec(dllexport)
+#endif
+int sqlite3_fts3_init(
   sqlite3 *db, 
   char **pzErrMsg,
   const sqlite3_api_routines *pApi