emqx4.3/changes/ce/perf-13634.en.md

Major optimization of the Durable Sessions feature.

• Idle durable subscribers no longer consume CPU.
• End-to-end latency of durable sessions has been improved.
• Frequency of durable storage queries has been significantly reduced.
• Optimized utilization of the cluster backplane network.

Configuration changes:

• Meaning of durable_sessions.idle_poll_interval parameter has changed. Now durable sessions are waken up immediately when new messages are written to the durable storage, so idle_poll_interval no longer affects end-to-end latency during normal operation.

From EMQX 5.8.1 on, idle polling is only used as a fallback mechanism for recovering from certain network errors. Therefore, the default value of idle_poll_interval has been increased. If this parameter has been customized in a previous version of EMQX, it should be increased as well.

New metrics:

• emqx_ds_poll_requests
• emqx_ds_poll_requests_fulfilled
• emqx_ds_poll_requests_dropped
• emqx_ds_poll_requests_expired
• emqx_ds_poll_request_sharing