Disable Metrics by default Issue#209
Test performance effect of 'default' hashCode #168
Try to optimize the Set in the AsyncRequest*Impl #205, Step 1: Abstracting pendingRequests in AsyncRequest*Impl
Try to optimize the Set in the AsyncRequest*Impl #205, Step 2: replacing getPendingResponseCount() with hasNoPendingResponses()
Try to optimize the Set in the AsyncRequest*Impl #205, Step 3: Only create the map if waiting for more then one response.