Bug #70236 Use_count: Wrong count for key at 0x27547278, 3 should be 4

• Submitted: 4 Sep 2013 5:05
• Modified: 15 Oct 2013 17:56
• Reporter: Shane Bester (Platinum Quality Contributor)
• Status: Closed
• Category: MySQL Server: Optimizer
• Severity: S3 (Non-critical)
• Version: 5.6.15
• OS: Any
• CPU Architecture: Any

[4 Sep 2013 5:05] Shane Bester

Description:
Version: '5.6.15-debug'  MySQL Community Server (GPL)
[Note] Use_count: Wrong count for key at 0x27547278, 3 should be 4
[Note] Use_count: Wrong count for key at 0x27547278, 3 should be 4

How to repeat:
#on debug builds of 5.6, 5.7.

drop table if exists t1;
create table `t1` (`a` int,`b` int,`c` int,primary key (`a`),key (`b`,`c`)) engine=innodb;
insert into t1 values(0,0,0);
select * from `t1` where c <> 0 and a < 0 and b <> 1;

Suggested fix:
Enable the assertion for this bug and run RQG so that we'll find all the cases.  The SEL_ARG::test_use_count contains assertions commented out:

 //DBUG_ASSERT(false); // Todo - enable and clean up mess

[15 Oct 2013 17:56] Paul DuBois

Noted in 5.6.15, 5.7.3 changelog.

Incorrect reference counting in the range optimizer module resulted
in potential for missing or duplicate rows in the query result set.

[21 Feb 2017 7:03] Laurynas Biveinis

Contrary to the above, this bug has not been fixed in 5.6, filed doc bug 85094.

The fix for this bug has caused bug 84736

[24 Feb 2017 1:06] Paul DuBois

Posted by developer:
 
Correction:
Fixed in 5.7.3 only (not 5.6.15).