Understanding Datasource Roles

All datasources within a dataservice have a specific role within the dataservice. The Primary (master) role is one that provides a source of replication information, and a Replica (slave) one that receives that information.

Role	Supplies Replication Data	Receives Replication Data	Load Balancing	Failover
master	Yes	No	Yes	Yes
slave	No	Yes	Yes	Yes
relay	Yes	Yes	Yes	Yes
standby	No	Yes	No	Yes
archive	No	Yes	Yes	No

More detailed information for each role:

• master (Primary)

  A datasource in a master role is providing a source for replication information to other datasources in the dataservice and is able to provide both read and write connections for applications.

• slave (Replica)

  A slave datasource is receiving data from a master and having that replicated data applied by Tungsten Cluster. Replicas are used for read-only operations by applications.

• relay

  A relay datasource receives replication data, from upstream primary nodes in remote clusters, and serves the downstream replicas within the same cluster.

  This role is specific to the passive cluster within an Composite Active/Passive topology, or within the cross-site sub-services within Composite Active/Active and Composite Dynamic Active/Active topologies.

  In the event of a failover between the active and passive cluster within a Composite Active/Passive configuration, the relay node will be promoted to the master role. During a switch, the old master will become the relay.

• standby

  A standby datasource receives replication data, but is never chosen by the connector to act as a read source by application clients. Standby datasources are therefore kept up to date with replication, but not used for load balancing.

  When a failover occurs, a standby datasource can be enabled as a standard slave and included in load-balanced operations.

• archive

  An archive datasource can be used to provide an active (up to date) copy of the data, without the datasource being used in the event of a failover. This can be useful for providing backup support, offline querying outside of the normal dataservice operations, or auditing purposes.