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Bug#50843: Filesort used instead of clustered index led to

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performance degradation.

Filesort + join cache combination is preferred to full index scan because it
is usually faster. But it's not the case when the index is clustered one.

Now test_if_skip_sort_order function prefers filesort only if index isn't
clustered.

mysql-test/r/innodb_mysql.result:
  Added a test case for the bug#50843.
mysql-test/t/innodb_mysql.test:
  Added a test case for the bug#50843.
sql/sql_select.cc:
  Bug#50843: Filesort used instead of clustered index led to
  performance degradation.
  Now test_if_skip_sort_order function prefers filesort only if index isn't
  clustered.
This commit is contained in:
Evgeny Potemkin
2010-02-26 14:17:00 +03:00
parent 6f78ef71d4
commit 2d4db52eda
3 changed files with 39 additions and 6 deletions
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14
mysql-test/r/innodb_mysql.result
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@ -2281,4 +2281,18 @@ CREATE TABLE t1 (a INT PRIMARY KEY) ENGINE=innodb ;
SELECT 1 FROM t1 JOIN t1 a USING(a) GROUP BY t1.a,t1.a;
1
DROP TABLE t1;
#
# Bug#50843: Filesort used instead of clustered index led to
# performance degradation.
#
create table t1(f1 int not null primary key, f2 int) engine=innodb;
create table t2(f1 int not null, key (f1)) engine=innodb;
insert into t1 values (1,1),(2,2),(3,3);
insert into t2 values (1),(2),(3);
explain select t1.* from t1 left join t2 using(f1) group by t1.f1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index NULL PRIMARY 4 NULL 3
1 SIMPLE t2 ref f1 f1 4 test.t1.f1 1 Using index
drop table t1,t2;
#
End of 5.1 tests