I'm using memcached for some caching in my Rails 3 app through the simple Rails.cache interface and now I'd like to do some background job processing with redis and resque.
I think they're different enough to warrant using both. On heroku though, there are separate fees to use both memcached and redis. Does it make sense to use both or should I migrate to just using redis?
I like using memcached for caching because least recently used keys automatically get pushed out of the cache and I don't need the cache data to persist. Redis is mostly new to me, but I understand that it's persistent by default and that keys do not expire out of the cache automatically.
EDIT: Just wanted to be more clear with my question. I know it's feasible to use only Redis instead of both. I guess I just want to know if there are any specific disadvantages in doing so? Considering both implementation and infrastructure, are there any reasons why I shouldn't just use Redis? (I.e., is memcached faster for simple caching?) I haven't found anything definitive either way.
Assuming that migrating from memcached to redis for the caching you already do is easy enough, I'd go with redis only to keep things simple.
In redis persistence is optional, so you can use it much like memcached if that is what you want. You may even find that making your cache persistent is useful to avoid lots of cache misses after a restart. Expiry is available also - the algorithm is a bit different from memcached, but not enough to matter for most purposes - see http://redis.io/commands/expire for details.