WAN Latency

Length: 221 words; Published: June 24, 2015; Updated: October 22, 2019; Category: Performance; Type: Best Practices

When using Galera Cluster over a WAN, remember that WAN links can have exceptionally high latency. You can check this by taking Round-Trip Time (RTT) measurements between cluster nodes. If there is a latency, you can correct for this by adjusting all of the temporal parameters.


To take RTT measurements, use ping on each cluster node to ping the others. For example, if you were to log into the node at, you might execute something like the following from the command-line:

$ ping -c 3

  PING ( 58(84) bytes of data.
  64 bytes from icmp_seq=1 ttl=64 time=0.736 ms
  64 bytes from icmp_seq=2 ttl=64 time=0.878 ms
  64 bytes from icmp_seq=3 ttl=64 time=12.7 ms

  --- ---

  3 packets transmitted, 3 received, 0% packet loss, time 2002ms
  rtt min/avg/max/mdev = 0.736/4.788/12.752/5.631 ms

Repeat this on each node in the cluster and note the highest value among them.

Parameters that relate to periods and timeouts, such as evs.join_retrans_period, must all use values that exceed the highest RTT measurement in the cluster.


This allows the cluster to compensate for the latency issues of the WAN links between the cluster nodes.