The implementations compared in the figure above are:
***Legacy:** uses the JSON-based synchronization to transfer all messages.
***Blobs:** uses the new BLOBs implemenation to transfer content of messages. Legacy sync is still used to transfer metadata.
***Blobs + session cache:** same as above, but also caches session in server-side, thus avoiding having to query couch for user authentication data on every request.
***Blobs + session cache + persistent http:** same as above, but also reuses HTTP connections on client side, thus avoiding having to open a new TLS/TCP connection for every request.