Configuring Drupal with multiple bins for memcached

In a recent article, we explained how to build memcached from source and  PHP memcache using PECL on Ubuntu Gutsy 7.10.

This article is a followup on how to configure memcache for Drupal, and how multiple bins help with performance.

Each bin in memcached correspond to one or more cache table in Drupal.

To do this, we first setup a start script for memcache that would start each bin with the correct size. This would go into /usr/local/bin/memcache.sh:

#!/bin/sh
case "$1" in
start) /usr/local/bin/memcached -d -u root -m 64  -p 11211
/usr/local/bin/memcached -d -u root -m 320 -p 11212
/usr/local/bin/memcached -d -u root -m 128 -p 11213
;;
stop)  killall memcached
;;
esac 

Then we need to change Drupal's settings.php to match that. You see that the page cache and filter cache each have their own bin, running on a separate instance of memcache. Everything else shares a "default" cache, which includes the menu cache and variables.

$conf = array(
'cache_inc' => './sites/all/modules/memcache/memcache.inc',
'memcache_servers' => array(
'localhost:11211' => 'default',
'localhost:11212' => 'page',
'localhost:11213' => 'filter',
),
'memcache_bins' => array(
'cache'        => 'default',
'cache_menu'   => 'default',
'cache_page'   => 'page',
'cache_filter' => 'filter',
),
);

Here are some statistics for each bin, after running for three weeks.

This one is for the default
bin, which is used for the "cache_menu" and "cache" tables.

The following bin is "page", and it is used for the "cache_page" table.

The filter
bin is for the cache_filter" table.

The page bin is the one that has the worst hits/misses ratio. The other two are very good. By separating the bins, we get better performance.