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Bug#41660: Sort-index_merge for non-first join table may

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require O(#scans) memory

When an index merge operation was restarted, it would
re-allocate the Unique object controlling the duplicate row
ID elimination. Fixed by making the Unique object a member
of QUICK_INDEX_MERGE_SELECT and thus reusing it throughout
the lifetime of this object.
This commit is contained in:
Martin Hansson
2010-06-24 15:21:23 +02:00
parent a08780df98
commit dac59fa9c3
5 changed files with 88 additions and 19 deletions
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35
mysql-test/r/error_simulation.result
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@@ -48,5 +48,40 @@ Got one of the listed errors
SET SESSION debug=DEFAULT;
DROP TABLE t1;
#
# Bug#41660: Sort-index_merge for non-first join table may require
# O(#scans) memory
#
CREATE TABLE t1 (a INT);
INSERT INTO t1 VALUES (0), (1), (2), (3), (4), (5), (6), (7), (8), (9);
CREATE TABLE t2 (a INT, b INT, filler CHAR(100), KEY(a), KEY(b));
INSERT INTO t2 SELECT 1000, 1000, 'filler' FROM t1 A, t1 B, t1 C;
INSERT INTO t2 VALUES (1, 1, 'data');
# the example query uses LEFT JOIN only for the sake of being able to
# demonstrate the issue with a very small dataset. (left outer join
# disables the use of join buffering, so we get the second table
# re-scanned for every record in the outer table. if we used inner join,
# we would need to have thousands of records and/or more columns in both
# tables so that the join buffer is filled and re-scans are triggered).
SET SESSION debug = '+d,only_one_Unique_may_be_created';
EXPLAIN
SELECT * FROM t1 LEFT JOIN t2 ON ( t2.a < 10 OR t2.b < 10 );
id select_type table type possible_keys key key_len ref rows Extra
x x x x x x x x x
x x x x x x x x x Using sort_union(a,b); Using where
SELECT * FROM t1 LEFT JOIN t2 ON ( t2.a < 10 OR t2.b < 10 );
a a b filler
0 1 1 data
1 1 1 data
2 1 1 data
3 1 1 data
4 1 1 data
5 1 1 data
6 1 1 data
7 1 1 data
8 1 1 data
9 1 1 data
SET SESSION debug = DEFAULT;
DROP TABLE t1, t2;
#
# End of 5.1 tests
#