Optimizing Phoenix Channels Performance with Erlang Garbage Collection

Erik Guzman explores a common issue faced by developers using Phoenix Channels for WebSocket connections, particularly with long-lived connections, which can lead to substantial memory consumption on the server. This was highlighted by Guzman's experience with his Stream Closed Captioner application for Twitch streamers and Zoom meetings, where memory usage could reach up to 6-7 gigabytes due to many simultaneous connections. Upon researching, he found that the underlying problem is related to the way the Erlang Virtual Machine (VM) handles garbage collection for long-lived processes, which can prevent memory from being freed up in a timely manner. He shares insights from the book 'Real-Time Phoenix' that suggest using the ERL_FULLSWEEP_AFTER environment variable to adjust the frequency of full-sweep garbage collections. By setting this to a lower number than the default of 65535, it forces the VM to clean up memory more often. In Guzman's case, adjusting this value to 20 resulted in a drastic reduction of memory usage from 6 gigabytes to around 3.5 gigabytes. This change had a significant positive impact on the application's performance and cost-efficiency. Guzman concludes by recommending 'Real-Time Phoenix' by Stephen Bussey for further reading and encourages developers to consider adjusting the ERL_FULLSWEEP_AFTER setting if they are facing similar issues with their real-time Phoenix Channels applications.