MDEV-21580: Allow packed sort keys in sort bufferbb-10.5-mdev6915-ext

This task deals with packing the sort key inside the sort buffer, which  would
lead to efficient usage of the memory allocated for the sort buffer.

The changes brought by this feature are
  1) Sort buffers would have sort keys of variable length
  2) The format for sort keys inside the sort buffer would look like
     |<sort_length><null_byte><key_part1><null_byte><key_part2>.......|
      sort_length is the extra bytes that are required to store the variable
      length of a sort key.
  3) When packing of sort key is done we store the ORIGINAL VALUES inside
     the sort buffer and not the STRXFRM form (mem-comparable sort keys).
  4) Special comparison function packed_keys_comparison() is introduced
     to compare 2 sort keys.

1 files changed, 73 insertions, 26 deletions

diff --git a/sql/field.cc b/sql/field.cc
index 1ce49b0bdfa..c9b29af1155 100644
--- a/sql/field.cc
+++ b/sql/field.cc
@@ -1013,8 +1013,15 @@ CPP_UNNAMED_NS_END
   Static help functions
 *****************************************************************************/
 
+/*
+  @brief
+    Create a fixed size sort key part
+
+  @param  buff           buffer where values are written
+  @param  length         fixed size of the sort column
+*/
 
-void Field::make_sort_key(uchar *buff,uint length)
+void Field::make_sort_key_part(uchar *buff,uint length)
 {
   if (maybe_null())
   {
@@ -1029,6 +1036,62 @@ void Field::make_sort_key(uchar *buff,uint length)
 }
 
 
+/*
+  @brief
+    Create a packed sort key part
+
+  @param  buff           buffer where values are written
+  @param  sort_field     sort column structure
+
+  @retval
+    length of the bytes written, does not include the NULL bytes
+*/
+uint
+Field::make_packed_sort_key_part(uchar *buff,
+                                 const SORT_FIELD_ATTR *sort_field)
+{
+  if (maybe_null())
+  {
+    if (is_null())
+    {
+      *buff++= 0;
+      return 0;  // For NULL values don't write any data
+    }
+    *buff++=1;
+  }
+  sort_string(buff, sort_field->original_length);
+  return sort_field->original_length;
+}
+
+
+uint
+Field_longstr::make_packed_sort_key_part(uchar *buff,
+                                         const SORT_FIELD_ATTR *sort_field)
+{
+  if (maybe_null())
+  {
+    if (is_null())
+    {
+      *buff++= 0;
+      return 0;   // For NULL values don't write any data
+    }
+    *buff++=1;
+  }
+  uchar *end= pack_sort_string(buff, sort_field);
+  return static_cast<int>(end-buff);
+}
+
+
+uchar*
+Field_longstr::pack_sort_string(uchar *to, const SORT_FIELD_ATTR *sort_field)
+{
+  String buf;
+  val_str(&buf, &buf);
+  return to + sort_field->pack_sort_string(to, buf.lex_cstring(),
+                                           field_charset());
+}
+
+
 /**
   @brief
   Determine the relative position of the field value in a numeric interval
@@ -5395,29 +5458,6 @@ static longlong read_native(const uchar *from, uint bytes)
 }
 #endif
 
-static void store_lowendian(ulonglong num, uchar *to, uint bytes)
-{
-  switch(bytes) {
-  case 1: *to= (uchar)num;    break;
-  case 2: int2store(to, num); break;
-  case 3: int3store(to, num); break;
-  case 4: int4store(to, num); break;
-  case 8: int8store(to, num); break;
-  default: DBUG_ASSERT(0);
-  }
-}
-
-static longlong read_lowendian(const uchar *from, uint bytes)
-{
-  switch(bytes) {
-  case 1: return from[0];
-  case 2: return uint2korr(from);
-  case 3: return uint3korr(from);
-  case 4: return uint4korr(from);
-  case 8: return sint8korr(from);
-  default: DBUG_ASSERT(0); return 0;
-  }
-}
 
 void Field_timestamp_hires::store_TIMEVAL(const timeval &tv)
 {
@@ -8526,8 +8566,15 @@ Binlog_type_info Field_blob::binlog_type_info() const
 
 uint32 Field_blob::sort_length() const
 {
-  return (uint32) (get_thd()->variables.max_sort_length + 
-                   (field_charset() == &my_charset_bin ? 0 : packlength));
+  return packlength == 4 ?
+    UINT_MAX32 :
+    (uint32) field_length + sort_suffix_length();
+}
+
+
+uint32 Field_blob::sort_suffix_length() const
+{
+  return field_charset() == &my_charset_bin ?  packlength : 0;
 }