Notes posted by kratob

Confusing log output

If you do a single Rails.cache.read('my_key'), your will usually see in your log something like

Cache read: my_key
Cache read: my_key
Cache write: my_key

Don’t worry about this.

What happens here is this: Before going to memcached, rails will first ask a local MemoryStore cache (which is responsible for the first and third line in the log), before falling through to memcached. This local cache is destroyed after each request.

Source is in activesupport/lib/active_support/cache/strategy/local_cache.rb.

Careful with scopes

Just like find, find_in_batches introduces an implicit scope into the block. So for example

Person.find_in_batches(:conditions => {:birthday => Date.today}) do |birthday_childs|
  Person.all.each do |person|
    person.send_presents_to(birthday_childs)
  end
end

does not work as expected, because the Person.all within the block will also find only persons with :conditions => {:birthday => Date.today}.