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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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11
sql/opt_range.cc
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@ -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;