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Bug #47123: Endless 100% CPU loop with STRAIGHT_JOIN

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The problem was in incorrect handling of predicates involving 
NULL as a constant value by the range optimizer.  
 
For example, when creating a SEL_ARG node from a condition of 
the form "field < const" (which would normally result in the 
"NULL < field < const" SEL_ARG),  the special case when "const" 
is NULL was not taken into account, so "NULL < field < NULL" 
was produced for the "field < NULL" condition. 
 
As a result, SEL_ARG structures of this form could not be 
further optimized which in turn could lead to incorrectly 
constructed SEL_ARG trees. In particular, code assuming SEL_ARG 
structures to always form a sequence of ordered disjoint 
intervals could enter an infinite loop under some 
circumstances. 
 
Fixed by changing get_mm_leaf() so that for any sargable 
predicate except "<=>" involving NULL as a constant, "empty" 
SEL_ARG is returned, since such a predicate is always false.
This commit is contained in:
Alexey Kopytov
2009-10-13 19:49:32 +04:00
parent f161723821
commit 5db734a896
3 changed files with 30 additions and 0 deletions
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9
mysql-test/r/range.result
View File

@ -1219,3 +1219,12 @@ explain select * from t2 where a=1000 and b<11;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 ref a a 5 const 502 Using where
drop table t1, t2;
#
# Bug #47123: Endless 100% CPU loop with STRAIGHT_JOIN
#
CREATE TABLE t1(a INT, KEY(a));
INSERT INTO t1 VALUES (1), (NULL);
SELECT * FROM t1 WHERE a <> NULL and (a <> NULL or a <= NULL);
a
DROP TABLE t1;
# End of 5.1 tests

10
mysql-test/t/range.test
View File

@ -1046,3 +1046,13 @@ explain select * from t2 where a=1000 and b<11;
drop table t1, t2;
--echo #
--echo # Bug #47123: Endless 100% CPU loop with STRAIGHT_JOIN
--echo #
CREATE TABLE t1(a INT, KEY(a));
INSERT INTO t1 VALUES (1), (NULL);
SELECT * FROM t1 WHERE a <> NULL and (a <> NULL or a <= NULL);
DROP TABLE t1;
--echo # End of 5.1 tests

11
sql/opt_range.cc
View File

@ -5887,6 +5887,17 @@ get_mm_leaf(RANGE_OPT_PARAM *param, COND *conf_func, Field *field,
goto end;
}
field->table->in_use->variables.sql_mode= orig_sql_mode;
/*
Any sargable predicate except "<=>" involving NULL as a constant is always
FALSE
*/
if (type != Item_func::EQUAL_FUNC && field->is_real_null())
{
tree= &null_element;
goto end;
}
str= (uchar*) alloc_root(alloc, key_part->store_length+1);
if (!str)
goto end;