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BUG#39185 - Cardinality for merge tables calculated incorrectly.

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Every subsequent query to a merge table with indexes was lowering
down cardinality.

The problem was that key statistics was not cleared when merge
children were detached. Causing next attach children perform
incremental key statistics calculation.

Fixed by clearing key statistics when attaching first child.
This commit is contained in:
Sergey Vojtovich
2009-02-05 17:03:47 +04:00
parent 3d543dd16d
commit 0acdf23f16
3 changed files with 34 additions and 1 deletions
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19
mysql-test/r/merge.result
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@ -2041,4 +2041,23 @@ EXPLAIN SELECT COUNT(*) FROM t4;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
DROP TABLE t1, t2, t3, t4;
CREATE TABLE t1(a INT, KEY(a));
INSERT INTO t1 VALUES(0),(1),(2),(3),(4);
ANALYZE TABLE t1;
Table Op Msg_type Msg_text
test.t1 analyze status OK
CREATE TABLE m1(a INT, KEY(a)) ENGINE=MERGE UNION=(t1);
SELECT CARDINALITY FROM INFORMATION_SCHEMA.STATISTICS WHERE TABLE_SCHEMA='test' AND TABLE_NAME='m1';
CARDINALITY
5
SELECT CARDINALITY FROM INFORMATION_SCHEMA.STATISTICS WHERE TABLE_SCHEMA='test' AND TABLE_NAME='m1';
CARDINALITY
5
SELECT CARDINALITY FROM INFORMATION_SCHEMA.STATISTICS WHERE TABLE_SCHEMA='test' AND TABLE_NAME='m1';
CARDINALITY
5
SELECT CARDINALITY FROM INFORMATION_SCHEMA.STATISTICS WHERE TABLE_SCHEMA='test' AND TABLE_NAME='m1';
CARDINALITY
5
DROP TABLE t1, m1;
End of 5.1 tests