Details
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Type:
Bug
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Status: Closed
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Resolution: Fixed
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Affects Version/s: None
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Fix Version/s: None
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Component/s: None
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Labels:
Description
Table elimination works in 5.3 release builds, even if one sets @@optimizer_switch to turn it off.
create table t1 (a int);
insert into t1 values (0),(1),(2),(3);
create table t2 (a int primary key, b int)
as select a, a as b from t1 where a in (1,2);
set optimizer_switch='table_elimination=on';
explain extended select t1.a from t1 left join t2 on t2.a=t1.a;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 4 100.00
Warnings:
Note 1003 select `test`.`t1`.`a` AS `a` from `test`.`t1` where 1
set optimizer_switch='table_elimination=off';
explain extended select t1.a from t1 left join t2 on t2.a=t1.a;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 4 100.00
Warnings:
Note 1003 select `test`.`t1`.`a` AS `a` from `test`.`t1` where 1
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Re: Table elimination works 5.3 release builds even if turned off
The problem occurs only in 5.3 because in 5.2 table_elimination=on/off flag is only present in debug builds.
Launchpad bug id: 884631
Re: Table elimination works 5.3 release builds even if turned off
The problem is because of this code in eliminate_tables();
#ifndef DBUG_OFF
if (!optimizer_flag(thd, OPTIMIZER_SWITCH_TABLE_ELIMINATION))
DBUG_VOID_RETURN; /* purecov: inspected */
#endif
The "#ifndef DBUG_OFF" part is left since the times when table_elimination=on/off was present only in debug builds.