FAQ paxos-single-replica-limit

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FAQ Paxos-single-replica-limit

What is paxos-single-replica-limit?

The paxos-single-replica-limit is a parameter within the service stanza that defines a minimum number of nodes in the cluster, at or below which replica records will not be stored. This means only master copies will be stored on the cluster.

What is the default value?

The default value for paxos-single-replica-limit is 1. This makes sense as there is no value to holding replica records in a single node cluster.

Can the parameter be set dynamically?

No, this is a static parameter and cannot be set with asinfo. It is unanimous meaning all nodes within the cluster must have the same value for the cluster to form. If an attempt is made to start a node where paxos-single-replica-limit is different to other nodes the behaviour is undefined. This implies that even if the node starts and joins the cluster it is not a safe or advisable procedure to attempt in a production environment.

Where might the parameter be set to a value greater than 0?

If a use case prioritised availability of new records and system resources are limited, it may not be desirable to wait until only 1 node remains before stopping storage of replicas.

Is paxos-single-replica-limit respected in a rack aware configuration?

Yes. Whether the nodes that go down are of the same group or different groups to the remaining nodes, the value for paxos-single-replica-limit will be respected.