Race condition when updating a field in Sidekiq

Question

I have a concurrency of two threads in Sidekiq and at one point I call the following method in one of my models:

def update_pending
  update(pending_stats: self.pending_stats + 1)
end

I would expect that when both jobs finish, the pending_stats attribute is two, but it is just one, even though both threads call that method.

How can I make sure that the two threads update actually with the correct value?

Answer 1

Try using increment_counter which is an atomic operation.

    def update_pending
      increment_counter(:pending_status, 1)
    end

This would execute following SQL:

    UPDATE ...
    SET pending_status = COALESCE(pending_status, 0) + 1
    WHERE ...