[rt-users] RT Performance - Intermittent slow spells

[Kenneth Marshall]

On Tue, Mar 17, 2009 at 12:49:14PM +1300, Aaron Guise wrote:
> Hi,
> We are currently having some intermittent problems where our RT stops
> responding.  I have isolated this I think to a database problem of some
> sort.  I turned on Slow Query logging and this is what MySQL picked up.  Any
> ideas what may cause such performance issues.  It is intermittent but very
> annoying when it does occur.  I have tuned the DB with mysqltuner and when
> it does run proper then it really hums along.
> 
> # Time: 090317 12:42:29
> # User at Host: rt[rt] @ localhost []
> # Query_time: 11  Lock_time: 0  Rows_sent: 1  Rows_examined: 0
> SELECT GET_LOCK('Apache-Session-288c54fb38d789956edc518ca4321abb', 3600);
> # User at Host: rt[rt] @ localhost []
> # Query_time: 11  Lock_time: 0  Rows_sent: 1  Rows_examined: 0
> SELECT GET_LOCK('Apache-Session-288c54fb38d789956edc518ca4321abb', 3600);
> # User at Host: rt[rt] @ localhost []
> # Query_time: 11  Lock_time: 0  Rows_sent: 1  Rows_examined: 0
> SELECT GET_LOCK('Apache-Session-288c54fb38d789956edc518ca4321abb', 3600);
> 
> -- 
> Regards
> 
> Aaron

Aaron,

Check the length of your session data. I expect that you have a couple
of very large sessions that a taxing your DB I/O subsystem. If you
delete them, the offending user will need to login again, but your
performance should be back to normal. I do not know what causes this
bloating of the session data, but my current 3000 entry session table
entries are all less than 75k. When I see this problem, there is usually
1 session in the 5-20MB range. Here is the query I use in PostgreSQL
which should be close to what you need:

SELECT id,length(a_session) FROM sessions ORDER BY length(a_session)
  DESC LIMIT 10;

This pruning could be done easily from a cronjob.

Cheers,
Ken