MySQL Bugs: #48137: procedure analyse() leaks memory when returning null

Bug #48137	procedure analyse() leaks memory when returning null
Submitted:	19 Oct 2009 4:24	Modified:	26 Apr 2011 15:50
Reporter:	Shane Bester (Platinum Quality Contributor)	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Server: General	Severity:	S2 (Serious)
Version:	5.0.85,5.1.39,5.1.41, 5.5.8	OS:	Any
Assigned to:		CPU Architecture:	Any
Tags:	Leak, memory leak, PROCEDURE ANALYSE

Description:
mysql> select distinctrow `a`
    -> from `t1` natural right outer join `t3`;
+------+
| a    |
+------+
| NULL |
+------+
1 row in set (1.01 sec)

116 bytes in 1 blocks are definitely lost in loss record 4 of 13
at: malloc (vg_replace_malloc.c:195)
by: proc_analyse_init( (sql_analyse.cc:74)
by: setup_procedure (procedure.cc:93)
by: JOIN::prepare (sql_select.cc:613)
by: mysql_select (sql_select.cc:2377)
by: handle_select (sql_select.cc:268)
by: execute_sqlcom_select (sql_parse.cc:5011)
by: mysql_execute_command(THD*) (sql_parse.cc:2206)
by: mysql_parse (sql_parse.cc:5931)
by: dispatch_command (sql_parse.cc:1213)
by: do_command(THD*) (sql_parse.cc:854)
by: handle_one_connection (sql_connect.cc:1127)

How to repeat:
run mysqld under valgrind then execute the sql:

drop table if exists `t1`,`t3`;
create table `t1`(`a` int)engine=myisam;
create table `t3`(`b` int)engine=innodb;
insert into `t3` values (1);
select distinctrow `a`
from `t1` natural right outer join `t3`
procedure analyse();

Suggested fix:
don't leak memory

I disagree with the affort put into fixing this bug.  Memory leaks are not a joking matter. They are near impossible to debug in live environments [unlike crashes, which are fairly basic].

The use-case is legitimate SQL requiring minimal select privs.
The fix is likely trivial here.

Noted in 5.1.58, 5.5.13, 5.6.3 changelogs.

PROCEDURE ANALYZE() could leak memory for NULL results, and could
return incorrect results if used with a LIMIT clause. 

CHANGESET - http://lists.mysql.com/commits/135391