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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.test
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@@ -2187,3 +2187,40 @@ eval explain extended $q;
set optimizer_switch= @save_optimizer_switch;
DROP TABLE books, wings;
--echo #
--echo # MDEV-17761: Odd optimizer choice with ORDER BY LIMIT and condition selectivity
--echo #
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 ();
--echo # rows must be around 1200, not 600:
explain extended
select * from t4 where b < 5000 order by 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;