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MDEV-17761: Odd optimizer choice with ORDER BY LIMIT and condition selectivity

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Make the "ORDER BY ... LIMIT n" optimizer take into account condition
selectivity data from EITS (not just from potential range accesses).
This commit is contained in:
Sergei Petrunia
2019-01-23 15:49:49 +03:00
parent 36a2a185fe
commit b7a784ae25
5 changed files with 145 additions and 0 deletions
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37
mysql-test/main/order_by.result
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@@ -3253,3 +3253,40 @@ Warnings:
Note 1003 select `test`.`wings`.`id` AS `wing_id`,`test`.`wings`.`department_id` AS `department_id` from `test`.`wings` semi join (`test`.`books`) where `test`.`books`.`library_id` = 8663 and `test`.`books`.`scheduled_for_removal` = 0 and `test`.`wings`.`id` = `test`.`books`.`wings_id` order by `test`.`wings`.`id`
set optimizer_switch= @save_optimizer_switch;
DROP TABLE books, wings;
#
# MDEV-17761: Odd optimizer choice with ORDER BY LIMIT and condition selectivity
#
create table t1(a int);
insert into t1 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
create table t2(a int);
insert into t2 select A.a + B.a* 10 + C.a * 100 from t1 A, t1 B, t1 C;
create table t3(a int);
insert into t3 select A.a + 1000 *B.a from t2 A, t1 B;
create table t4 (
a int,
b int,
c int,
filler1 char(255),
filler2 char(255),
key(a)
);
insert into t4 select a,a,a, a,a from t3;
set @tmp_h=@@histogram_size, @tmp_u=@@use_stat_tables,
@tmp_o=@@optimizer_use_condition_selectivity;
set histogram_size=100;
set use_stat_tables=preferably;
set optimizer_use_condition_selectivity=4;
analyze table t4 persistent for columns(b) indexes ();
Table Op Msg_type Msg_text
test.t4 analyze status Engine-independent statistics collected
test.t4 analyze status Table is already up to date
# rows must be around 1200, not 600:
explain extended
select * from t4 where b < 5000 order by a limit 600;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t4 index NULL a 5 NULL 1188 100.00 Using where
Warnings:
Note 1003 select `test`.`t4`.`a` AS `a`,`test`.`t4`.`b` AS `b`,`test`.`t4`.`c` AS `c`,`test`.`t4`.`filler1` AS `filler1`,`test`.`t4`.`filler2` AS `filler2` from `test`.`t4` where `test`.`t4`.`b` < 5000 order by `test`.`t4`.`a` limit 600
set histogram_size=@tmp_h, use_stat_tables=@tmp_u,
optimizer_use_condition_selectivity=@tmp_o;
drop table t1,t2,t3,t4;