What does happen if cluster is out of quorum?


For example we have a 4-node cluster. In such case there is an epsilon on one of the nodes to have possibility to form a quorum if half of nodes lost. But what will happen if 2 nodes in one HA simultaneously fail and epsilon was on one the lost nodes? I understand that it’s quite rare situation, but our discussions started because of such situation. 2 nodes in HA failed because of backplane, but epsilon was on one of survived nodes.

So again. 4 nodes cluster. 2 nodes in HA fail simultaneously. There is no epsilon in the cluster. What does happen with data access from survived nodes?


I’m going to assume you are using redundancy-2 if you are concerned with HA. If you lose two leaf nodes that are not a replication pair, you will continue to have access to all the data. We don’t automatically fail over the master aggregator (MA). If the MA fails then you must fail it over manually by promoting a child aggregator to be master. The MA controls cluster membership.

Here’ some related documentation: https://docs.memsql.com/operational-manual/v6.7/managing-high-availability/