database/mariadb
1
0
Fork 0
mirror of https://github.com/MariaDB/server.git synced 2025-07-29 05:21:33 +03:00
Code Activity

MDEV-19474: Histogram statistics are used even with optimizer_use_condition_selectivity=3

Browse Source 
The issue here was histogram statistics were being used even when
the level of optimizer_use_condition_selectivity doesn't allow
usage of statistics from histogram.

The histogram statistics are read for a table only when
optimizer_use_condition_selectivity > 3. But the TABLE structure can be
stored in the internal table cache and be reused for the next query.
So in this case the histogram statistics will be available for the next query.

The fix would be to make sure to use the histogram statistics only when
optimizer_use_condition_selectivity > 3.
This commit is contained in:
Varun Gupta
2021-02-09 20:27:21 +05:30
parent e926964cb8
commit a461e4d306
5 changed files with 111 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

11
sql/sql_statistics.h
View File

@ -212,6 +212,17 @@ public:
bool is_available() { return get_size() > 0 && get_values(); }
/*
This function checks that histograms should be usable only when
1) the level of optimizer_use_condition_selectivity > 3
2) histograms have been collected
*/
bool is_usable(THD *thd)
{
return thd->variables.optimizer_use_condition_selectivity > 3 &&
is_available();
}
void set_value(uint i, double val)
{
switch (type) {