Core group coordinator
Every core group has a coordinator that manages high availability activities between the core group members, including failover of HA singleton services and distribution of live server state data to other members.
The coordinator can use large amounts of CPU and JVM heap.
The coordinator workload can be divided over multiple coordinator instances running on different core group members, enabling the sharing of resource costs across machines.
Coordinator election
If core group member hosting a coordinator instance fails, and the HA manager elects a replacement coordinator.
Informational messages are logged in SystemOut.log when a core group member is elected as a coordinator...
HMGR0206I: The coordinator is an active coordinator for core group DefaultCoreGroup...and if a core group member is no longer an elected coordinator...
HMGR0207I: The coordinator was previously an active coordinator for core group DefaultCoreGroup but has lost leadership.Electing a new coordinator consumes a lot network traffic and CPU. Specify a preferred coordinator server to eliminate the need to make frequent coordinator changes.
Multiple coordinators
You can specify the number of coordinators. The default is one, which is sufficient for most installations. Consider increasing if the core group coordinator member uses noticeably more memory or CPU than other core group members.
Preferred servers
When configuring a core group, we can specify the core group members the HA manager should use as coordinators. Preferred coordinator servers should be core group processes that are cycled as infrequently as possible, and hosted on machines with excess capacity.
When coordinators are elected during a view change, the HA manager checks for a list of preferred servers. If there is a list, the HA manager selects a server from that list as the coordinator. If there is no list, the HA manager selects the view member with the lexically lowest name.
Related concepts
Core group View Synchrony Protocol
Core groups (HA domains)
Related tasks
Change the number of core group coordinators
Configure core group preferred coordinators