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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. 

mysql-test/r/partition_pruning.result:
  Fixed a broken test case.
mysql-test/r/range.result:
  Added a test case for bug #47123.
mysql-test/r/subselect.result:
  Fixed a broken test cases.
mysql-test/t/range.test:
  Added a test case for bug #47123.
sql/opt_range.cc:
  Fixed 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
2009-10-17 00:19:51 +04:00
parent e066294824
commit f6868a4eb4
5 changed files with 33 additions and 4 deletions
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3
mysql-test/r/subselect.result
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@ -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;