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Bug #55656: mysqldump can be slower after bug 39653 fix.

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After fix for bug 39653 the shortest available secondary index was used for
full table scan. Primary clustered key was used only if no secondary index
can be used. However, when chosen secondary index includes all fields of the
table being scanned it's better to use primary index since the amount of
data to scan is the same but the primary index is clustered.
Now the find_shortest_key function takes this into account.


mysql-test/suite/innodb/r/innodb_mysql.result:
  Added a test case for the bug#55656.
mysql-test/suite/innodb/t/innodb_mysql.test:
  Added a test case for the bug#55656.
sql/sql_select.cc:
  Bug #55656: mysqldump can be slower after bug #39653 fix.
  The find_shortest_key function now prefers clustered primary key
  if found secondary key includes all fields of the table.
This commit is contained in:
Evgeny Potemkin
2010-08-26 13:31:04 +04:00
parent e5a59eee5a
commit b4dc600af9
3 changed files with 125 additions and 18 deletions
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58
mysql-test/suite/innodb/r/innodb_mysql.result
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@ -2529,4 +2529,62 @@ SELECT * FROM t1 FOR UPDATE;
SELECT * FROM t1 GROUP BY (SELECT a FROM t2 LIMIT 1 FOR UPDATE) + t1.a;
ERROR 40001: Deadlock found when trying to get lock; try restarting transaction
DROP TABLE t1,t2;
#
# Bug#55656: mysqldump can be slower after bug #39653 fix
#
CREATE TABLE t1 (a INT , b INT, c INT, d INT,
KEY (b), PRIMARY KEY (a,b)) ENGINE=INNODB;
INSERT INTO t1 VALUES (1,1,1,1), (2,2,2,2), (3,3,3,3);
EXPLAIN SELECT COUNT(*) FROM t1;
id 1
select_type SIMPLE
table t1
type index
possible_keys NULL
key b
key_len 4
ref NULL
rows 3
Extra Using index
DROP INDEX b ON t1;
CREATE INDEX b ON t1(a,b);
EXPLAIN SELECT COUNT(*) FROM t1;
id 1
select_type SIMPLE
table t1
type index
possible_keys NULL
key b
key_len 8
ref NULL
rows 3
Extra Using index
DROP INDEX b ON t1;
CREATE INDEX b ON t1(a,b,c);
EXPLAIN SELECT COUNT(*) FROM t1;
id 1
select_type SIMPLE
table t1
type index
possible_keys NULL
key b
key_len 13
ref NULL
rows 3
Extra Using index
DROP INDEX b ON t1;
CREATE INDEX b ON t1(a,b,c,d);
EXPLAIN SELECT COUNT(*) FROM t1;
id 1
select_type SIMPLE
table t1
type index
possible_keys NULL
key PRIMARY
key_len 8
ref NULL
rows 3
Extra Using index
DROP TABLE t1;
#
End of 5.1 tests