Default Bernoulli Sampling implementationbb-10.4-vicentiu-histograms10.4-vicentiu-histograms

2 files changed, 56 insertions, 22 deletions

diff --git a/sql/handler.h b/sql/handler.h
index 8f9ddc01174..d40e986fd9d 100644
--- a/sql/handler.h
+++ b/sql/handler.h
@@ -1906,6 +1906,11 @@ enum enum_stats_auto_recalc { HA_STATS_AUTO_RECALC_DEFAULT= 0,
                               HA_STATS_AUTO_RECALC_ON,
                               HA_STATS_AUTO_RECALC_OFF };
 
+enum sample_mode {
+  HA_SAMPLE_BERNOULLI= 0,
+  HA_SAMPLE_SYSTEM,
+};
+
 /**
   A helper struct for schema DDL statements:
     CREATE SCHEMA [IF NOT EXISTS] name [ schema_specification... ]
@@ -2940,9 +2945,11 @@ public:
   /** Length of ref (1-8 or the clustered key length) */
   uint ref_length;
   FT_INFO *ft_handler;
-  enum init_stat { NONE=0, INDEX, RND, RANDOM };
+  enum init_stat { NONE=0, INDEX, RND, SAMPLE };
   init_stat inited, pre_inited;
 
+  double sample_fraction= 0;
+  enum sample_mode sample_mode;
   const COND *pushed_cond;
   /**
     next_insert_id is the next value which should be inserted into the
@@ -3105,21 +3112,25 @@ public:
   virtual int prepare_range_scan(const key_range *start_key, const key_range *end_key)
   { return 0; }
 
-  virtual int ha_random_sample_init(THD *thd, ha_rows estimate_rows_read)
+  int ha_random_sample_init(THD *thd, enum sample_mode mode, double fraction)
     __attribute__((warn_unused_result))
   {
     DBUG_ENTER("ha_random_sample_init");
-    inited= RANDOM;
-    DBUG_RETURN(random_sample_init(thd, estimate_rows_read));
+    DBUG_ASSERT(inited==NONE);
+    int result;
+    sample_mode= mode;
+    sample_fraction= fraction;
+    inited= (result= random_sample_init(mode, fraction)) ? NONE : SAMPLE;
+    DBUG_RETURN(result);
   }
-  virtual int ha_random_sample(uchar *buf)
+  int ha_random_sample(uchar *buf)
     __attribute__((warn_unused_result))
   {
     DBUG_ENTER("ha_random_sample");
-    DBUG_ASSERT(inited == RANDOM);
+    DBUG_ASSERT(inited == SAMPLE);
     DBUG_RETURN(random_sample(buf));
   }
-  virtual int ha_random_sample_end() __attribute__((warn_unused_result))
+  int ha_random_sample_end()
   {
     DBUG_ENTER("ha_random_sample_end");
     inited= NONE;
@@ -4439,12 +4450,25 @@ private:
   /* Note: ha_index_read_idx_map() may bypass index_init() */
   virtual int index_init(uint idx, bool sorted) { return 0; }
   virtual int index_end() { return 0; }
-  virtual int random_sample_init(MYSQL_THD thd, ha_rows estimate_rows_read) { return 0; } ;
+  virtual int random_sample_init(enum sample_mode mode, double fraction)
+  {
+    return rnd_init(TRUE);
+  }
   virtual int random_sample(uchar *buf)
   {
-    return HA_ERR_WRONG_COMMAND;
+    int rc;
+    THD *thd= ha_thd();
+    do
+    {
+      rc= rnd_next(buf);
+
+      if (rc == HA_ERR_RECORD_DELETED)
+        continue;
+
+    } while (rc == HA_ERR_RECORD_DELETED || thd_rnd(thd) > sample_fraction);
+    return rc;
   }
-  virtual int random_sample_end() { return 0; };
+  virtual int random_sample_end() { return rnd_end(); }
   /**
     rnd_init() can be called two times without rnd_end() in between
     (it only makes sense if scan=1).
diff --git a/sql/sql_statistics.cc b/sql/sql_statistics.cc
index daebc5d0b38..b8b99015745 100644
--- a/sql/sql_statistics.cc
+++ b/sql/sql_statistics.cc
@@ -2727,12 +2727,15 @@ int collect_statistics_for_table(THD *thd, TABLE *table)
   Field *table_field;
   ha_rows rows= 0;
   handler *file=table->file;
+  double sample_fraction;
 
   DBUG_ENTER("collect_statistics_for_table");
 
   table->collected_stats->cardinality_is_null= TRUE;
   table->collected_stats->cardinality= 0;
 
+  table->file->info(HA_STATUS_VARIABLE);
+
   for (field_ptr= table->field; *field_ptr; field_ptr++)
   {
     table_field= *field_ptr;   
@@ -2743,19 +2746,27 @@ int collect_statistics_for_table(THD *thd, TABLE *table)
 
   restore_record(table, s->default_values);
 
-  rc= file->ha_random_sample_init(thd, 100);
-  rc= file->ha_random_sample(table->record[0]);
-  table_field->collected_stats->add(0);
-  rc= file->ha_random_sample_end();
 
+  if (file->records() < 30000)
+  {
+    sample_fraction= 1;
+  }
+  else
+  {
+    sample_fraction= std::fmin(
+                (30000 + 4096 * log(200 * file->records())) /
+                  (file->records() + 1), 1);
+  }
+
+
+  /* Fetch samples from the table to collect statistics on table's columns */
 
-  /* Perform a full table scan to collect statistics on 'table's columns */
-  /*
-  if (!(rc= file->ha_rnd_init(TRUE)))
-  {  
+  if (!(rc= file->ha_random_sample_init(thd, HA_SAMPLE_BERNOULLI,
+                                        sample_fraction)))
+  {
     DEBUG_SYNC(table->in_use, "statistics_collection_start");
 
-    while ((rc= file->ha_rnd_next(table->record[0])) != HA_ERR_END_OF_FILE)
+    while ((rc= file->ha_random_sample(table->record[0])) != HA_ERR_END_OF_FILE)
     {
       if (thd->killed)
         break;
@@ -2775,10 +2786,9 @@ int collect_statistics_for_table(THD *thd, TABLE *table)
         break;
       rows++;
     }
-    file->ha_rnd_end();
+    file->ha_random_sample_end();
   }
   rc= (rc == HA_ERR_END_OF_FILE && !thd->killed) ? 0 : 1;
-  */
   /* 
     Calculate values for all statistical characteristics on columns and
     and for each field f of 'table' save them in the write_stat structure
@@ -2787,7 +2797,7 @@ int collect_statistics_for_table(THD *thd, TABLE *table)
   if (!rc)
   {
     table->collected_stats->cardinality_is_null= FALSE;
-    table->collected_stats->cardinality= rows;
+    table->collected_stats->cardinality= rows / sample_fraction;
   }
 
   bitmap_clear_all(table->write_set);