[horde] Memcache server questions

[Andrew Morgan]

On Wed, 12 Nov 2008, Steve Devine wrote:

>  We are about a month away from full release of our Horde implementation.
> Twice we have had hard failures of our session management system.
> We are using memcache on a separate server. Its a SunX4100 with 8gigs of 
> available ram, we gave memcached 4Gigs to use and it had been running fine. 
> Yesterday our Communication manager sent out a huge mass mailing inviting 
> people to try the system and after an hour it went right in the tank.
> We are in the process of getting another machine to run memcached on line so 
> we can do failover but this whole thing spooks me a bit.
> I have read many times on this list that memcache is the best way to handle 
> sessions on a large installation. Is this still the feeling of the list?
> One of the problems is when the apache server cannot write the session it 
> just hangs and the user gets a blank screen. Soon it seems to cascade out of 
> control and stopping and restarting the memcache process did not seem to 
> help.
> If I decide to abandon the memcache server in favor of mysql am I heading 
> down the same road? Anyone out there with experience in either of these 
> methods care to comment?
> Thanks
> /sd

I've been running memcached on a Sun x4100 with 8GB of RAM.  I gave it 2GB 
of RAM because this machine also runs our MySQL instance for Horde.  I'm 
running Debian Etch, stock packages.  It has been rock-solid for us.

Can you be more specific when you say "it went right in the tank"?  Did 
memcached stop responding?

Sessions are really really hard on MySQL.  The session table is updated so 
frequently that it is almost never able to use the MySQL query cache.  You 
can also have locking problems unless you use InnoDB tables.  Even still, 
every session update must be written to disk, which is a lot slower than 
memory.  Last time I checked, it isn't possible to use memory-based MySQL 
tables for the session table either (locking not supported? I forget).

 	Andy