def with_connection
    connection_id = current_connection_id
    fresh_connection = true unless @reserved_connections[connection_id]
    yield connection
  ensure
    release_connection(connection_id) if fresh_connection
  end
def with_connection
    connection_id = current_connection_id
    fresh_connection = true unless @reserved_connections[connection_id]
    yield connection
  ensure
    release_connection(connection_id) if fresh_connection
  end
If a connection already exists yield it to the block. If no connection
 exists checkout a connection, yield it to the block, and checkin the
 connection when finished.