Is it recommended to store PHP Sessions in MemCache?

php memcached
Adam picture Adam · Dec 19, 2012 · Viewed 51.5k times · Source

I'm working with a couple of Web Servers behind a Load Balancer and I can enable Sticky Sessions to hold a user to the one specific Web Servers - this will work.

I have been reading about PHP Sessions & MemCache. I must say what I've read is a touch confusing as some pages say its a good idea and others the opposite.

Questions:

  1. is it possible to keep php sessions in memcache?
  2. is it better to use sticky sessions over memcache?
  3. what are the problems with php sessions in memcache - note: I can get enough cache (amazon so its expandable).

Answer

FredTheWebGuy picture FredTheWebGuy · Dec 19, 2012

1: YES. And I strongly recommend storing PHP sessions in Memcached. Here's why:

Memcached is great for storing small chunks of data that are frequently accessed by the database and filesystem.

Memcached was designed specifically for sessions. It was originally the brainchild of the lead developer of livejournal.com, and later used to also cache the content of users' posts. The benefit was immediate: most of the action was taking place in memory. Page load times greatly improved.

Thankfully, PHP and Apache have an easy implementation to handle sessions with Memcached. Simply install with a few shell commands

example for debian:

sudo apt-get -t stable install php5-memcached

and

change your php.ini settings to something similar to:

(taken from http://www.dotdeb.org/2008/08/25/storing-your-php-sessions-using-memcached/)

 session.save_handler = memcache
 ; change server:port to fit your needs...
 session.save_path="tcp://server:port?persistent=1&weight=1&
timeout=1&retry_interval=15"

The key is the session.save_path

It will no longer point to a relative file path on your server. APC was mentioned- APC for the caching of .php files used by the program. APC and Memcached will reduce IO signicantly and leave Apache free to serve resources,such as images, faster.

2: No

3: The fundamental disadvantage of using Memcached is data volatility

Session data is not persistent in Memcached. So if and when the server crashes, all data in memory is lost. Everyone will have to log in again.

And then you have memory consumption...

Remember: the sessions are stored in the memory. If your website handles a large amount of concurrent users, you may have to shell out a little extra money for a larger memory allocation.

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