Installation on multiple Hosts and Caching

[perlgeek]

Hi all,

we have OTRS 3.2.9 installed on four hosts; two for the web frontend behind a load balancer, and two hosts that run the postmaster.

Now we have the problems that the caches diverge on these hosts. For example a new ticket comes in through the postmaster, and the result of TicketGet are cached on that server. Next I use the web frontend to set the ticket state to "sleeping" (a custom state, I think), and the webserver invalidates its own cache, but not that of the postmaster host. A follow-up email is sent to the postmaster, it retrieves the ticket from the cache, the cached state is still "open", and it doesn't wake up the ticket.

How do other people deal with these issues?

First we have tried to put the cache files on an NFS share, but the cache needs file locking, and locking and NFS are natural enemies, it seems. Even it one gets an NFS share where locking "works", it occasionally hangs for 20s or so to release a lock, which is unacceptable for a web server.
Now I'm investigating a common Redis caching backend for all four hosts, but a call to AgentTicketGet fetches about 130 caches, and the network latency adds up to about 200ms for all those lookups -- a step in the wrong direction, in terms of performance.

Any other ideas, or even better, existing solutions?

[jojo]

we are using a memcached backend, which exclusivly is used on customer projects

[perlgeek]

Have you measured how much time the requests to memcached take?

Also, have you managed to use authentication in the memcached backend? (The OTRS hosts don't run in an isolated network, so we to take care that not everybody can read the cache)