Galera Flow Control Pause Events
warningGalera/PXC cluster experiencing flow control pauses due to replication lag between nodes. Slower nodes trigger flow control to prevent unbounded lag, causing write stalls across the entire cluster and reducing overall throughput.
mysql.galera.wsrep_flow_control_paused > 0.1 (>10% time paused) or mysql.galera.wsrep_flow_control_sent rate > 10/sec, with mysql.galera.wsrep_local_recv_queue_avg > 100
Identify lagging node by comparing mysql.galera.wsrep_local_recv_queue across all nodes. Check mysql.galera.wsrep_local_state to ensure all nodes are SYNCED (state 4). Review node resource utilization - lagging node may be CPU, I/O, or network constrained. Configure flow control thresholds: gcs.fc_limit (default 16) and gcs.fc_factor (default 1.0). If specific node consistently lags: 1) Scale up that node, 2) Check for competing workloads, 3) Verify network latency between nodes. Monitor mysql.galera.wsrep_cert_deps_distance - low distance indicates limited parallelization opportunity.