DatabaseCleaner improperly starts and ends transactions for ActiveRecord

[ryanong]

If there is more than one connection in the connection pool DatabaseCleaner will only begin the transaction on one of the connections.
https://github.com/rails/rails/blob/master/activerecord/lib/active_record/fixtures.rb#L979

Any ActiveRecord call afterwards will use the next connection in the pool which does not have a transaction.

When DatabaseCleaner closes the transaction, it will only do so on the next active connection. Thus leaving a connection with an active transaction in the connection pool which can deadlock when doing a deletion cleanup or any table modifications.

DatabaseCleaner should start and end transactions the same way ActiveRecord does by collecting all available connections and starting transactions on all of them.

start: https://github.com/rails/rails/blob/06a9e18e646845ded0f0a46a14c1eb6b3a14e55a/activerecord/lib/active_record/fixtures.rb#L949
end: https://github.com/rails/rails/blob/06a9e18e646845ded0f0a46a14c1eb6b3a14e55a/activerecord/lib/active_record/fixtures.rb#L967

[lulalala]

@ryanong the code line numbers are off because master changed. Can you reference line numbers by some commit please?

[ryanong]

@lulalala fixed