Re: [Sqlrelay-discussion] Complex Queries Cause Mysql Connection to segfault

[David M. <dav...@fi...>]

I wonder if this is a mysql bug?

If the line:

if ((queryresult=mysql_stmt_execute(stmt))) {

is where it's crashing, the only possibility is that mysql_stmt_execute
is crashing.  Aside from a bug insidy mysql_stmt_execute, the only thing
that could cause a crash is if "stmt" is messed up somehow.

I'll take a look at the code that initializes stmt.  It's possible that
I'm doing something wrong there.

Dave
dav...@fi...

On Mon, 2007-03-19 at 18:11 -0500, Chris Coyle wrote:
> I've run into a some situations where complex queries in a certain
> sequence cause the connection handler to segfault which results in a
> cursor error from the listener.
> 
> Mysql Version: mysql-5.0.x-max
> SQLRelay Version: 0.38 - 0.39 (from cvs) (++ autoreconnect patch)
> Pertinent mysql settings: "wait_timeout = 10"
> 
> sql to generate table schema from mysqldump (sans comments):
> DROP TABLE IF EXISTS `sqlrelay`;
> CREATE TABLE `sqlrelay` (
>   `var1` varchar(25) default NULL,
>   `var2` varchar(25) default NULL,
>   `var3` varchar(25) default NULL,
>   `var4` varchar(25) default NULL
> ) ENGINE=MyISAM DEFAULT CHARSET=latin1;
> LOCK TABLES `sqlrelay` WRITE;
> INSERT INTO `sqlrelay` VALUES
> ('one','two','three','four'),('one','two','three','four'),('one','two','three','four');
> UNLOCK TABLES;
> 
> testsql.sql
>  ----
> SELECT var1, var2, var3, COALESCE(var4,'whatever') as var4 FROM
> test_sqlrelay.sqlrelay ORDER BY var1 ASC LIMIT 0,70;
> select count(*) as numResults from test_sqlrelay.sqlrelay limit 10;
> 
> testsql.sh
>  ----
> #!/bin/sh
> for I in `seq 10`; do
>         /usr/local/sqlrelay/bin/sqlrsh -id <mysql> testsql.sql
>         echo -e "[  $I  ]\n"
>         sleep 10
> done
> 
> Running this script with that sql on a freshly started sqlrelay
> instance (it seems to vary otherwise) will result in a segfault and
> cursor error on the second pass.
> 
> In gdb I was able to track it down to:
>  -- mysqlconnection.C:437 --
> if ((queryresult=mysql_stmt_execute(stmt))) {
> 
> Now here's where it gets weird.  If you do reverse the statements in
> testsql.sql (do the select count() first) then this error does NOT
> occur.
> 
> There are other examples where I've found this behavior, but they're
> far more sporadic.
> 
> I'll continue to try to track this further on my end, but if you need
> any further details, please let me know.
> 
> Thanks for your time,
> 
>  - Chris
> 
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