What is the default expiry time for Rails cache?

Question

I've done some googling and couldn't find the answer to this question. Rails allows to specify expiry times for its cache like that:

Rails.cache.fetch("my_var", :expires_in => 10.seconds) 

But what happens if I specify nothing:

Rails.cache.fetch("my_var") 

It never expires? Is there a default value? How can I explicitly define something that never expires?

Answer 1

It really depends on which cache storage you're using. Rails provides several, one of them most popular is Memcached. One of key features of Memcached is that it automatically expires old unused records, so you can forget about :expire option.

Other Rails cache storages, like memory storage or redis storage will keep will not expire date unless you explicitly specify when to do that.

More about how cache key expiration works in Rails.

Answer 2

Using Dalli for memcached (who doesn't), the default expiry time is never, as @Rahul says. You don't have to worry about garbage collection, as @icem says, memcached throw out the old unused records.

See the official dalli documentation:

Expires_in default is 0, which means never 

https://github.com/mperham/dalli#configuration

you can set the global expiry time for dalli

config.cache_store = :dalli_store, { expires_in: 1.day} 

and for better individual control:

Rails.cache.write "some_cache_key", some_cachable_string, expires_in: 3.hours 

the new doc http://apidock.com/rails/ActiveSupport/Cache/Store/write doesn't say much, but the old does: http://apidock.com/rails/ActiveSupport/Cache/MemCacheStore/write

manually expire a cache (if some event occurred):

Rails.cache.delete "some_cache_key"