Storing Symfony2 sessions in memcached

config.yml

imports:                                                                                                                                                                                                           
    # ....
    - { resource: services/session.yml }


framework:
    # ....
    session:
      handler_id:     session.handler.memcached

gistfile1.txt

aptitude install memcached php5-memcached

parameters.yml

parameters:
    # ...

    session_memcached_host:     localhost
    session_memcached_port:     11211
    session_memcached_prefix:   sess
    session_memcached_expire:   3600

session_services.yml

services:
    session.memcached:
        class: Memcached
        arguments:
            persistent_id: %session_memcached_prefix%
        calls:
            - [ addServer, [ %session_memcached_host%, %session_memcached_port% ]]

    session.handler.memcached:
        class:     Symfony\Component\HttpFoundation\Session\Storage\Handler\MemcachedSessionHandler
        arguments: [@session.memcached, { prefix: %session_memcached_prefix%, expiretime: %session_memcached_expire% }]

HUGE caveat here... Spent several hours figuring out what was going on.

If you are using Apache prefork, giving the persistent_id when instantiating the service creates a connection to memcached that lasts for as long as the Apache worker child stays alive (this can be a good thing... less overhead). However, the addServer call does not check for duplicates; this causes the memcached server to be listed in the server list and a connection to be opened once for every single request served by the worker.

The default Ubuntu settings are for a maximum of 400 workers, each able to handle 10000 requests before being killed. That means there might be as many as 4,000,000 open connections to the memcached server.

When we hit the memcached open connection limit of 1024, we were no longer able to store or retrieve any sessions from that point forward because the old connections just wouldn't die. There are two possible fixes for this:

1. Create a wrapper class for the built-in Memcached class that checks for duplicates before adding the server.
2. Don't use persistent connections - remove lines 4 & 5 in the session_services.yml snippet above.

Short term (because it's easier) I've gone with #2 - testing shows it's stable for now. There's obviously a performance overhead that would be negated by implementing #1.

@cmenning Could you please show up your #1 gist?

https://gist.github.com/elmariachi111/5637669a028c29e3973a better late than never ;)

see: http://php.net/manual/en/memcached.construct.php#93536

@cmenning you just made my day! Thanks a lot man!!