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

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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
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34
mysql-test/r/selectivity_innodb.result
View File

@@ -1920,6 +1920,40 @@ HEX(a) b
set optimizer_use_condition_selectivity= @save_optimizer_use_condition_selectivity;
set histogram_size=@save_histogram_size;
DROP TABLE t1;
#
# MDEV-19474: Histogram statistics are used even with optimizer_use_condition_selectivity=3
#
CREATE TABLE t1(a int);
INSERT INTO t1 values (1),(2),(2),(3),(4);
SET optimizer_use_condition_selectivity=4;
SET histogram_size= 255;
set use_stat_tables='preferably';
ANALYZE TABLE t1 PERSISTENT FOR ALL;
Table Op Msg_type Msg_text
test.t1 analyze status Engine-independent statistics collected
test.t1 analyze status OK
EXPLAIN EXTENDED SELECT * FROM t1 WHERE a=2;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 5 39.84 Using where
Warnings:
Note 1003 select `test`.`t1`.`a` AS `a` from `test`.`t1` where `test`.`t1`.`a` = 2
SET optimizer_use_condition_selectivity=3;
# filtered should show 25 %
EXPLAIN EXTENDED SELECT * FROM t1 WHERE a=2;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 5 25.00 Using where
Warnings:
Note 1003 select `test`.`t1`.`a` AS `a` from `test`.`t1` where `test`.`t1`.`a` = 2
FLUSH TABLES;
EXPLAIN EXTENDED SELECT * FROM t1 WHERE a=2;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 5 25.00 Using where
Warnings:
Note 1003 select `test`.`t1`.`a` AS `a` from `test`.`t1` where `test`.`t1`.`a` = 2
set optimizer_use_condition_selectivity= @save_optimizer_use_condition_selectivity;
set histogram_size=@save_histogram_size;
set use_stat_tables= @save_use_stat_tables;
DROP TABLE t1;
# End of 10.2 tests
set @@global.histogram_size=@save_histogram_size;
set optimizer_switch=@save_optimizer_switch_for_selectivity_test;