Commit 8e931fe5 authored by Alexey Kopytov's avatar Alexey Kopytov

Bug #47123: Endless 100% CPU loop with STRAIGHT_JOIN

 
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. 
parent 0e11bad5
......@@ -1272,10 +1272,9 @@ INSERT INTO t1 VALUES (1, '2009-01-01'), (2, NULL);
# test with an invalid date, which lead to item->null_value is set.
EXPLAIN PARTITIONS SELECT * FROM t1 WHERE b < CAST('2009-04-99' AS DATETIME);
id select_type table partitions type possible_keys key key_len ref rows Extra
1 SIMPLE t1 p20090401 ALL NULL NULL NULL NULL 2 Using where
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
Warnings:
Warning 1292 Incorrect datetime value: '2009-04-99'
Warning 1292 Incorrect datetime value: '2009-04-99'
DROP TABLE t1;
CREATE TABLE t1
(a INT NOT NULL AUTO_INCREMENT,
......
......@@ -1398,3 +1398,12 @@ a < 10;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t3 range a a 5 NULL 8 Using where; Using index
DROP TABLE t1, t2, t3;
#
# 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
......@@ -4403,8 +4403,7 @@ FROM t1
WHERE a = 230;
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
2 DEPENDENT SUBQUERY st1 index NULL a 5 NULL 2 Using index
2 DEPENDENT SUBQUERY st2 index b b 5 NULL 2 Using where; Using index; Using join buffer
2 DEPENDENT SUBQUERY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
SELECT MAX(b), (SELECT COUNT(*) FROM st1,st2 WHERE st2.b <= t1.b)
FROM t1
WHERE a = 230;
......
......@@ -1171,3 +1171,14 @@ a < 5 OR
a < 10;
DROP TABLE t1, t2, t3;
--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
......@@ -5891,6 +5891,17 @@ 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;
......
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