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Fix for bug #31207: Test "join_nested" shows different strategy on IA64

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CPUs / Intel's ICC compile

The bug is a combination of two problems:

1. IA64/ICC MySQL binaries use glibc's qsort(), not the one in mysys.

2. The order relation implemented by join_tab_cmp() is not transitive,
i.e. it is possible to choose such a, b and c that (a < b) && (b < c)
but (c < a). This implies that result of a sort using the relation
implemented by join_tab_cmp() depends on the order in which
elements are compared, i.e. the result is implementation-specific. Since
choose_plan() uses qsort() to pre-sort the
join tables using join_tab_cmp() as a compare function, the results of
the sorting may vary depending on qsort() implementation.

It is neither possible nor important to implement a better ordering
algorithm in join_tab_cmp(). Therefore the only way to fix it is to
force our own qsort() to be used by renaming it to my_qsort(), so we don't depend
on linker to decide that.

This patch also "fixes" bug #20530: qsort redefinition violates the
standard.
This commit is contained in:
kaa@polly.(none)
2007-10-17 20:08:58 +04:00
parent 80a2d47b22
commit 6d1f3e8de5
21 changed files with 62 additions and 46 deletions
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18
sql/sql_select.cc
View File

@ -3658,7 +3658,7 @@ update_ref_and_keys(THD *thd, DYNAMIC_ARRAY *keyuse,JOIN_TAB *join_tab,
{
KEYUSE key_end,*prev,*save_pos,*use;
qsort(keyuse->buffer,keyuse->elements,sizeof(KEYUSE),
my_qsort(keyuse->buffer,keyuse->elements,sizeof(KEYUSE),
(qsort_cmp) sort_keyuse);
bzero((char*) &key_end,sizeof(key_end)); /* Add for easy testing */
@ -4371,8 +4371,9 @@ choose_plan(JOIN *join, table_map join_tables)
Apply heuristic: pre-sort all access plans with respect to the number of
records accessed.
*/
qsort(join->best_ref + join->const_tables, join->tables - join->const_tables,
sizeof(JOIN_TAB*), straight_join?join_tab_cmp_straight:join_tab_cmp);
my_qsort(join->best_ref + join->const_tables,
join->tables - join->const_tables, sizeof(JOIN_TAB*),
straight_join ? join_tab_cmp_straight : join_tab_cmp);
if (straight_join)
{
@ -4421,6 +4422,17 @@ choose_plan(JOIN *join, table_map join_tables)
ptr1 pointer to first JOIN_TAB object
ptr2 pointer to second JOIN_TAB object
NOTES
The order relation implemented by join_tab_cmp() is not transitive,
i.e. it is possible to choose such a, b and c that (a < b) && (b < c)
but (c < a). This implies that result of a sort using the relation
implemented by join_tab_cmp() depends on the order in which
elements are compared, i.e. the result is implementation-specific.
Example:
a: dependent = 0x0 table->map = 0x1 found_records = 3 ptr = 0x907e6b0
b: dependent = 0x0 table->map = 0x2 found_records = 3 ptr = 0x907e838
c: dependent = 0x6 table->map = 0x10 found_records = 2 ptr = 0x907ecd0
RETURN
1 if first is bigger
-1 if second is bigger