*** The Galera software is designed so that all nodes are only as fast as their slowest node

Step 1 – Detect the node slowing down the cluster

  1. Check the amount of pause events a node has sent due to flow control on each node (lower is better)
    • SHOW STATUS LIKE ‘wsrep_flow_control_sent’;
  2. Check the average of the received queue length since the last status query on each node (lower is better)
    • SHOW STATUS LIKE ‘wsrep_local_recv_queue_avg’;
  3. Nodes that return values much higher than 0.0 indicates that it cannot apply write-sets as fast as they are received and can generate replication throttling for the whole cluster.

Step 2 – Fix the node slowing down the cluster

  1. To immediately speed up the performance, comment out the slow node from the haproxy configuration (if using ha as the load balancer)
  2. Find what is different about this node and solve accordingly.
    • CPUs
    • Disk IO
    • Network
    • RAM

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