MDEV-17032: Estimates are higher for partitions of a table with @@use_stat_tables= PREFERABLY

Varun Gupta · Varun Gupta · commit 4886d14827c6 · 2018-12-07T19:59:45.000+05:30
The problem here is EITS statistics does not calculate statistics for the partitions of the table.
So a temporary solution would be to not read EITS statistics for partitioned tables.

Also disabling reading of EITS for columns that participate in the partition list of a table.
diff --git a/mysql-test/r/partition.result b/mysql-test/r/partition.result
@@ -2645,3 +2645,103 @@ Warnings:
 Note	1517	Duplicate partition name p2
 DEALLOCATE PREPARE stmt;
 DROP TABLE t1;
+#
+# MDEV-17032: Estimates are higher for partitions of a table with @@use_stat_tables= PREFERABLY
+#
+create table t0(a int);
+insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+create table t1(a int);
+insert into t1 select A.a + B.a* 10 + C.a * 100 from t0 A, t0 B, t0 C;
+create table t2 (
+part_key int,
+a int,
+b int
+) partition by list(part_key) (
+partition p0 values in (0),
+partition p1 values in (1),
+partition p2 values in (2),
+partition p3 values in (3),
+partition p4 values in (4)
+);
+insert into t2
+select mod(a,5), a/100, mod(a,5) from t1;
+set @save_use_stat_tables= @@use_stat_tables;
+set @save_optimizer_use_condition_selectivity=@@optimizer_use_condition_selectivity;
+#
+# Tests using stats provided by the storage engine
+#
+explain extended select * from t2 where part_key=1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	200	100.00	Using where
+Warnings:
+Note	1003	select `test`.`t2`.`part_key` AS `part_key`,`test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b` from `test`.`t2` where (`test`.`t2`.`part_key` = 1)
+explain partitions select * from t2 where part_key=1;
+id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t2	p1	ALL	NULL	NULL	NULL	NULL	200	Using where
+explain extended select * from t2 where  part_key in (1,2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	400	100.00	Using where
+Warnings:
+Note	1003	select `test`.`t2`.`part_key` AS `part_key`,`test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b` from `test`.`t2` where (`test`.`t2`.`part_key` in (1,2))
+explain partitions select * from t2 where  part_key in (1,2);
+id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t2	p1,p2	ALL	NULL	NULL	NULL	NULL	400	Using where
+explain extended select * from t2 where b=5;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	1000	100.00	Using where
+Warnings:
+Note	1003	select `test`.`t2`.`part_key` AS `part_key`,`test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b` from `test`.`t2` where (`test`.`t2`.`b` = 5)
+explain partitions select * from t2 where b=5;
+id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t2	p0,p1,p2,p3,p4	ALL	NULL	NULL	NULL	NULL	1000	Using where
+explain extended select * from t2 partition(p0)  where b=1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	200	100.00	Using where
+Warnings:
+Note	1003	select `test`.`t2`.`part_key` AS `part_key`,`test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b` from `test`.`t2` PARTITION (`p0`) where (`test`.`t2`.`b` = 1)
+set @save_histogram_size=@@histogram_size;
+set @@histogram_size=100;
+set @@use_stat_tables= PREFERABLY;
+set @@optimizer_use_condition_selectivity=4;
+analyze table t2;
+Table	Op	Msg_type	Msg_text
+test.t2	analyze	status	Engine-independent statistics collected
+test.t2	analyze	status	OK
+#
+# Tests using EITS
+#
+# filtered should be 100
+explain extended select * from t2 where part_key=1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	200	100.00	Using where
+Warnings:
+Note	1003	select `test`.`t2`.`part_key` AS `part_key`,`test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b` from `test`.`t2` where (`test`.`t2`.`part_key` = 1)
+explain partitions select * from t2 where part_key=1;
+id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t2	p1	ALL	NULL	NULL	NULL	NULL	200	Using where
+# filtered should be 100
+explain extended select * from t2 where  part_key in (1,2);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	400	100.00	Using where
+Warnings:
+Note	1003	select `test`.`t2`.`part_key` AS `part_key`,`test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b` from `test`.`t2` where (`test`.`t2`.`part_key` in (1,2))
+explain partitions select * from t2 where  part_key in (1,2);
+id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t2	p1,p2	ALL	NULL	NULL	NULL	NULL	400	Using where
+explain extended select * from t2 where b=5;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	1000	19.80	Using where
+Warnings:
+Note	1003	select `test`.`t2`.`part_key` AS `part_key`,`test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b` from `test`.`t2` where (`test`.`t2`.`b` = 5)
+explain partitions select * from t2 where b=5;
+id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t2	p0,p1,p2,p3,p4	ALL	NULL	NULL	NULL	NULL	1000	Using where
+explain extended select * from t2 partition(p0)  where b=1;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	200	19.80	Using where
+Warnings:
+Note	1003	select `test`.`t2`.`part_key` AS `part_key`,`test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b` from `test`.`t2` PARTITION (`p0`) where (`test`.`t2`.`b` = 1)
+set @@use_stat_tables= @save_use_stat_tables;
+set @@optimizer_use_condition_selectivity= @save_optimizer_use_condition_selectivity;
+set @@histogram_size= @save_histogram_size;
+drop table t0,t1,t2;
diff --git a/mysql-test/t/partition.test b/mysql-test/t/partition.test
@@ -2897,3 +2897,64 @@ EXECUTE stmt;
 DEALLOCATE PREPARE stmt;
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-17032: Estimates are higher for partitions of a table with @@use_stat_tables= PREFERABLY
+--echo #
+
+create table t0(a int);
+insert into t0 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+
+create table t1(a int);
+insert into t1 select A.a + B.a* 10 + C.a * 100 from t0 A, t0 B, t0 C;
+
+
+create table t2 (
+  part_key int,
+  a int,
+  b int
+) partition by list(part_key) (
+  partition p0 values in (0),
+  partition p1 values in (1),
+  partition p2 values in (2),
+  partition p3 values in (3),
+  partition p4 values in (4)
+);
+insert into t2
+select mod(a,5), a/100, mod(a,5) from t1;
+
+set @save_use_stat_tables= @@use_stat_tables;
+set @save_optimizer_use_condition_selectivity=@@optimizer_use_condition_selectivity;
+--echo #
+--echo # Tests using stats provided by the storage engine
+--echo #
+explain extended select * from t2 where part_key=1;
+explain partitions select * from t2 where part_key=1;
+explain extended select * from t2 where  part_key in (1,2);
+explain partitions select * from t2 where  part_key in (1,2);
+explain extended select * from t2 where b=5;
+explain partitions select * from t2 where b=5;
+explain extended select * from t2 partition(p0)  where b=1;
+
+
+set @save_histogram_size=@@histogram_size;
+set @@histogram_size=100;
+set @@use_stat_tables= PREFERABLY;
+set @@optimizer_use_condition_selectivity=4;
+analyze table t2;
+--echo #
+--echo # Tests using EITS
+--echo #
+--echo # filtered should be 100
+explain extended select * from t2 where part_key=1;
+explain partitions select * from t2 where part_key=1;
+--echo # filtered should be 100
+explain extended select * from t2 where  part_key in (1,2);
+explain partitions select * from t2 where  part_key in (1,2);
+explain extended select * from t2 where b=5;
+explain partitions select * from t2 where b=5;
+explain extended select * from t2 partition(p0)  where b=1;
+
+set @@use_stat_tables= @save_use_stat_tables;
+set @@optimizer_use_condition_selectivity= @save_optimizer_use_condition_selectivity;
+set @@histogram_size= @save_histogram_size;
+drop table t0,t1,t2;
diff --git a/sql/opt_range.cc b/sql/opt_range.cc
@@ -3322,14 +3322,17 @@ bool create_key_parts_for_pseudo_indexes(RANGE_OPT_PARAM *param,
 {
   Field **field_ptr;
   TABLE *table= param->table;
+  partition_info *part_info= NULL;
+  #ifdef WITH_PARTITION_STORAGE_ENGINE
+    part_info= table->part_info;
+  #endif
   uint parts= 0;
 
   for (field_ptr= table->field; *field_ptr; field_ptr++)
   {
-    Column_statistics* col_stats= (*field_ptr)->read_stats;
-    if (bitmap_is_set(used_fields, (*field_ptr)->field_index)
-       && col_stats && !col_stats->no_stat_values_provided()
-       && !((*field_ptr)->type() == MYSQL_TYPE_GEOMETRY))
+    Field *field= *field_ptr;
+    if (bitmap_is_set(used_fields, field->field_index) &&
+        is_eits_usable(field))
       parts++;
   }
 
@@ -3347,12 +3350,10 @@ bool create_key_parts_for_pseudo_indexes(RANGE_OPT_PARAM *param,
   uint max_key_len= 0;
   for (field_ptr= table->field; *field_ptr; field_ptr++)
   {
-    if (bitmap_is_set(used_fields, (*field_ptr)->field_index))
+    Field *field= *field_ptr;
+    if (bitmap_is_set(used_fields, field->field_index))
     {
-      Field *field= *field_ptr;
-      Column_statistics* col_stats= field->read_stats;
-      if (field->type() == MYSQL_TYPE_GEOMETRY ||
-           !col_stats || col_stats->no_stat_values_provided())
+      if (!is_eits_usable(field))
         continue;
 
       uint16 store_length;
diff --git a/sql/partition_info.cc b/sql/partition_info.cc
@@ -3164,6 +3164,23 @@ void partition_info::print_debug(const char *str, uint *value)
     DBUG_PRINT("info", ("parser: %s", str));
   DBUG_VOID_RETURN;
 }
+
+bool partition_info::field_in_partition_expr(Field *field) const
+{
+  uint i;
+  for (i= 0; i < num_part_fields; i++)
+  {
+    if (field->eq(part_field_array[i]))
+      return TRUE;
+  }
+  for (i= 0; i < num_subpart_fields; i++)
+  {
+    if (field->eq(subpart_field_array[i]))
+      return TRUE;
+  }
+  return FALSE;
+}
+
 #else /* WITH_PARTITION_STORAGE_ENGINE */
  /*
    For builds without partitioning we need to define these functions
diff --git a/sql/partition_info.h b/sql/partition_info.h
@@ -384,6 +384,7 @@ class partition_info : public Sql_alloc
   bool is_full_part_expr_in_fields(List<Item> &fields);
 public:
   bool has_unique_name(partition_element *element);
+  bool field_in_partition_expr(Field *field) const;
 };
 
 uint32 get_next_partition_id_range(struct st_partition_iter* part_iter);
diff --git a/sql/sql_statistics.cc b/sql/sql_statistics.cc
@@ -30,6 +30,7 @@
 #include "opt_range.h"
 #include "my_atomic.h"
 #include "sql_show.h"
+#include "sql_partition.h"
 
 /*
   The system variable 'use_stat_tables' can take one of the
@@ -3589,6 +3590,22 @@ void set_statistics_for_table(THD *thd, TABLE *table)
     (use_stat_table_mode <= COMPLEMENTARY ||
      !table->stats_is_read || read_stats->cardinality_is_null) ?
     table->file->stats.records : read_stats->cardinality;
+
+  /*
+    For partitioned table, EITS statistics is based on data from all partitions.
+
+    On the other hand, Partition Pruning figures which partitions will be
+    accessed and then computes the estimate of rows in used_partitions.
+
+    Use the estimate from Partition Pruning as it is typically more precise.
+    Ideally, EITS should provide per-partition statistics but this is not
+    implemented currently.
+  */
+  #ifdef WITH_PARTITION_STORAGE_ENGINE
+    if (table->part_info)
+      table->used_stat_records= table->file->stats.records;
+  #endif
+
   KEY *key_info, *key_info_end;
   for (key_info= table->key_info, key_info_end= key_info+table->s->keys;
        key_info < key_info_end; key_info++)
@@ -3904,3 +3921,31 @@ bool is_stat_table(const char *db, const char *table)
   }
   return false;
 }
+
+/*
+  Check wheter we can use EITS statistics for a field or not
+
+  TRUE : Use EITS for the columns
+  FALSE: Otherwise
+*/
+
+bool is_eits_usable(Field *field)
+{
+  partition_info *part_info= NULL;
+  #ifdef WITH_PARTITION_STORAGE_ENGINE
+    part_info= field->table->part_info;
+  #endif
+  /*
+    (1): checks if we have EITS statistics for a particular column
+    (2): Don't use EITS for GEOMETRY columns
+    (3): Disabling reading EITS statistics for columns involved in the
+         partition list of a table. We assume the selecticivity for
+         such columns would be handled during partition pruning.
+  */
+  Column_statistics* col_stats= field->read_stats;
+  if (col_stats && !col_stats->no_stat_values_provided() &&        //(1)
+      field->type() != MYSQL_TYPE_GEOMETRY &&                      //(2)
+      (!part_info || !part_info->field_in_partition_expr(field)))  //(3)
+    return TRUE;
+  return FALSE;
+}
diff --git a/sql/sql_statistics.h b/sql/sql_statistics.h
@@ -109,6 +109,7 @@ double get_column_range_cardinality(Field *field,
                                     key_range *max_endp,
                                     uint range_flag);
 bool is_stat_table(const char *db, const char *table);
+bool is_eits_usable(Field* field);
 
 class Histogram
 {

Original file line number	Diff line number	Diff line change
`@@ -109,6 +109,7 @@ double get_column_range_cardinality(Field *field,`
`109`	`109`	`key_range *max_endp,`
`110`	`110`	`uint range_flag);`
`111`	`111`	`bool is_stat_table(const char db, const char table);`
	`112`	`+bool is_eits_usable(Field* field);`
`112`	`113`
`113`	`114`	`class Histogram`
`114`	`115`	`{`