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

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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.
This commit is contained in:
Varun Gupta
2018-12-07 02:12:22 +05:30
parent 12b1ba195c
commit 4886d14827
7 changed files with 235 additions and 9 deletions
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45
sql/sql_statistics.cc
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@ -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;
}