Rails.cache with Memcache and a File cache for fragments

One of the things that we do at TouchLocal is provide Search Engine Optimised pages that drive traffic to the site through the UK National Directory pages. As you can imagine, there’s quite a lot of data intensive processing that is required to generate these pages, and there are an awful lot of them. As it changes relatively rarely, for a long time we had been caching these pages in a Rails Action cache so that the headers and footers are not cached but the content is.

As we enhanced the caching strategy through the site, and the Rails support for Memcache improved, we changed the Rails cache to use Memcache. This by implication meant that the default cache we had been using for actions (the filestore cache) was no longer used and the infrastructure team could not flush the cache in the same way it previously had.

So that we could use the Rails.cache helper and still have the benefit of the Action cache, we changed our production environment configuration to look like this:

# Namespace for memcache to automatically flush on app version updates.
# APP_REVISION is updated automatically via asking the Version Control System
ns = "dir_#{RAILS_ENV}_#{$persona}_#{APP_REVISION}"

# MC_ADDRESSES constant is put into the root namespace - we use it for other things
::MC_ADDRESSES = ['', '', '']

# Rails.cache is memcache
config.cache_store = :mem_cache_store, MC_ADDRESSES,{:namespace => ns}

# Force the ActionController cache store to be the file one as per the previous default.
config.action_controller.cache_store = :file_store, "#{RAILS_ROOT}/tmp/cache"

Happy days.