Re: [Sqlrelay-discussion] infinite loop

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

I ran into a similar problem a while back.  The mysql api does
erroneously return a db has gone away error when certain queries are
run.  I believe in some cases, a query returns multiple result sets and
the code has to decide which one to use, and the first one has that
error in it, or something like that.  I think I ran into the issue when
trying to get stored functions working.  There were lots of references
to similar problems on the web.  I haven't come up with a good solution
yet, but it's on my list :/

Dave
dav...@fi...

On Sat, 2006-07-22 at 10:04 -0700, Devananda wrote:
> Dear List,
> 
> sqlrelay is regularly getting stuck in an infinite reconnect loop on 
> both servers on which I am running it right now. This seems to happen 
> /most often/ after hours of inactivity, but not always. I've spent a 
> week tracking this down, and have found where the MySQL C API is 
> returning an unexpected result, and sqlrelay goes into an infinite loop 
> because of it.
> 
> First, the platform; sqlrelay pulled from CVS a few weeks ago, Fedora 
> 4/5, and MySQL 5.0.18-5.0.22.
> 
> The loop itself happens inside the sqlrconnection_svr::handleQuery 
> function, where the inline comments clearly state "loop here to handle 
> down databases" :) The problem is that the MySQL C API (erroneously?) 
> returns an error message (CR_SERVER_GONE_ERROR) at mysqlconnection.C:542
> 
> if ((queryresult=mysql_stmt_execute(stmt))) {
> 
> As a result, sqlrconnection_svr::processQuery returns FALSE, which 
> triggers sqlrconnection_svr::handleError, which can not returnError() 
> because the database appears to be down, and therefor calls reLogIn(). 
> However, the database is not actually down, and sqlrelay reconnects to 
> it easily, tries to rerun the initial query, and gets the same return 
> value of CR_SERVER_GONE_ERROR, thus beginning the loop again.
> 
> Running sqlr-status during this time shows number of connections 
> skyrocketing, and asking MySQL to "SHOW STATUS" shows the number of 
> client connections (Aborted_clients and Connections) to be increasing as 
> well. "SHOW PROCESSLIST" also displays sqlrelay's connections, which are 
> being established and closed as fast as the server is able.
> 
> This looks as though it could be caused by the bug reported at 
> http://bugs.mysql.com/bug.php?id=19927.
> 
> I have added some code to detect and break out of the infinite loop, 
> hoping that would patch sqlrelay while MySQL fixes their bugs, however, 
> simply breaking out of the loop does not sufficiently fix what ever is 
> wrong. Any further debugging is beyond my abilities :(
> 
> If anyone can help, it would be very appreciated. We are on a pretty 
> tight development schedule, and this is really slowing us down. If 
> anyone needs to see a sqlrelay debug file, let me know and I'll send it 
> off-list.
> 
> 
> 
> Best Regards,
> Devananda van der Veen
> 
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