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Bug#48483 crash in get_best_combination()

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The crash happens because greedy_serach
can not determine best plan due to
wrong inner table dependences. These
dependences affects join table sorting
which performs before greedy_search starting.
In our case table which has real 'no dependences'
should be put on top of the list but it does not
happen as inner tables have no dependences as well.
The fix is to exclude RAND_TABLE_BIT mask from
condition which checks if table dependences
should be updated.
This commit is contained in:
Sergey Glukhov 2010-03-24 14:37:28 +04:00
parent 774cba9505
commit 658cf9e481
3 changed files with 41 additions and 1 deletions
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17
mysql-test/r/join.result
View file

@ -913,4 +913,21 @@ ON t4.a = t5.a
ON t1.a = t3.a;
a a a a a a
DROP TABLE t1,t2,t3,t4,t5,t6;
#
# Bug#48483: crash in get_best_combination()
#
CREATE TABLE t1(f1 INT);
INSERT INTO t1 VALUES (1),(2);
CREATE VIEW v1 AS SELECT 1 FROM t1 LEFT JOIN t1 AS t2 on 1=1;
EXPLAIN EXTENDED
SELECT 1 FROM v1 right join v1 AS v2 ON RAND();
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 2
1 SIMPLE t2 ALL NULL NULL NULL NULL 2
1 SIMPLE t1 ALL NULL NULL NULL NULL 2
1 SIMPLE t2 ALL NULL NULL NULL NULL 2
Warnings:
Note 1003 select 1 AS `1` from `test`.`t1` left join `test`.`t1` `t2` on((1 = 1)) left join (`test`.`t1` left join `test`.`t1` `t2` on((1 = 1))) on(rand()) where 1
DROP VIEW v1;
DROP TABLE t1;
End of 5.0 tests.

12
mysql-test/t/join.test
View file

@ -713,4 +713,16 @@ FROM
DROP TABLE t1,t2,t3,t4,t5,t6;
--echo #
--echo # Bug#48483: crash in get_best_combination()
--echo #
CREATE TABLE t1(f1 INT);
INSERT INTO t1 VALUES (1),(2);
CREATE VIEW v1 AS SELECT 1 FROM t1 LEFT JOIN t1 AS t2 on 1=1;
EXPLAIN EXTENDED
SELECT 1 FROM v1 right join v1 AS v2 ON RAND();
DROP VIEW v1;
DROP TABLE t1;
--echo End of 5.0 tests.

13
sql/sql_select.cc
View file

@ -4819,6 +4819,11 @@ greedy_search(JOIN *join,
if (best_extension_by_limited_search(join, remaining_tables, idx, record_count,
read_time, search_depth, prune_level))
DBUG_RETURN(TRUE);
/*
'best_read < DBL_MAX' means that optimizer managed to find
some plan and updated 'best_positions' array accordingly.
*/
DBUG_ASSERT(join->best_read < DBL_MAX);
if (size_remain <= search_depth)
{
@ -8431,8 +8436,14 @@ simplify_joins(JOIN *join, List<TABLE_LIST> *join_list, COND *conds, bool top)
we still make the inner tables dependent on the outer tables.
It would be enough to set dependency only on one outer table
for them. Yet this is really a rare case.
Note:
RAND_TABLE_BIT mask should not be counted as it
prevents update of inner table dependences.
For example it might happen if RAND() function
is used in JOIN ON clause.
*/
if (!(prev_table->on_expr->used_tables() & ~prev_used_tables))
if (!((prev_table->on_expr->used_tables() & ~RAND_TABLE_BIT) &
~prev_used_tables))
prev_table->dep_tables|= used_tables;
}
}