From 8e931fe53c55e203b285f30c892f24f106b56249 Mon Sep 17 00:00:00 2001 From: Alexey Kopytov Date: Sat, 17 Oct 2009 00:19:51 +0400 Subject: 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. --- mysql-test/r/range.result | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'mysql-test/r/range.result') diff --git a/mysql-test/r/range.result b/mysql-test/r/range.result index c98a7696ea6..0d44e79b39a 100644 --- a/mysql-test/r/range.result +++ b/mysql-test/r/range.result @@ -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 -- cgit v1.2.1