The multi-shard query coordinator, a component of the shard catalog, can be kept highly available and scaled to meet its workload with these recommendations.

The availability of the multi-shard coordinator impacts proxy-routing based workloads, so it is highly recommended that the coordinator be protected with Data Guard in Maximum Availability protection mode (zero data loss failover) with fast-start failover enabled. The coordinator may optionally be Oracle RAC-enabled for additional availability and scalability.

To improve the scalability and availability of multi-shard query workloads, Oracle Active Data Guard standby shard catalog databases in read-only mode can act as multi-shard query coordinators. For each active replica of the catalog database, a special coordinator service, GDS$COORDINATOR.cloud_name (where cloud_name is the value specified for the configname parameter in the GDSCTL CREATE SHARDCATALOG command, and is oradbcloud by default) is running and registered on all shard directors.

Clients can connect to this service on any of the replicas and perform multi-shard queries, allowing shard directors to distribute the multi-shard query workload with respect to runtime load balancing and decrease the load on in the primary shard catalog, which is the central component of Oracle Globally Distributed Database.

Additionally, if the database’s region is set, and the client specifies the region in the connection string, a shard director routes a connection with respect to regional affinity.

Availability of the multi-shard query coordinator has zero impact on workloads using direct routing.