Add missing super in prune_thread_cache method

[eugeneius]

Followup to #50938.

QueryCache::ConnectionPoolConfiguration is prepended to ConnectionPool and its prune_thread_cache method doesn't call super, so this method was never called. It's also unnecessary: reaped connections are already removed from @thread_cached_conns by the remove_connection_from_thread_cache call in steal!.

[byroot]

It's also unnecessary: reaped connections are already removed from @thread_cached_conns by the remove_connection_from_thread_cache call in steal!

That's no longer fully true though, not in testing at least because of the connection pinning. Now when you are using transactional fixtures, the same connection my be associated to multiple threads, but still only has one official owner, hence this pruning.

The missing super is definitely a mistake, and it probably had limited consequence because that's an edge case that only happens in test but we should fix it, not remove the whole thing.

[eugeneius]

I originally just added the missing call to super, but then tried to write a test for it and couldn't see a case where it would be needed. Thanks for the pointer to #50999, I see now since checkout returns the pinned connection it happens here:

rails/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb

Lines 178 to 180 in 6260b6b

	def connection
	@thread_cached_conns[ActiveSupport::IsolatedExecutionState.context] ||= checkout
	end

I'll just add the call to super, sorry for second guessing you!

[byroot]

sorry for second guessing you!

Absolutely not, I make as many mistake as the next person.

[eugeneius]

As demonstrated here, so do I 😄