Cluster Messages

Messages operating at cluster scope — global barriers and cluster-wide configuration.

All broadcast messages implicitly carry SharedCluster via the Broadcaster.

Message	Dispatch	ExclusiveRequired	ResourceKey
FlushAll	Broadcast: all PChannels	Yes (all PChannels)	ExclusiveCluster
AlterReplicateConfig	Broadcast: all PChannels	Yes (all PChannels)	ExclusiveCluster
AlterWAL	Broadcast: all PChannels	Yes (all PChannels)	ExclusiveCluster
AlterResourceGroup	Broadcast: CChannel	No	ExclusiveCluster
DropResourceGroup	Broadcast: CChannel	No	ExclusiveCluster

• FlushAll: Flushes ALL growing segments across ALL collections on ALL PChannels.
• AlterReplicateConfig: Changes replication topology — enabling, disabling, or switching PRIMARY/SECONDARY roles.
• AlterWAL: Switches WAL backend implementation across the entire cluster.
• AlterResourceGroup: Creates, updates, or transfers nodes between query resource groups.
• DropResourceGroup: Removes a resource group after verifying no replicas are loaded in it.

Key Invariants

• FlushAll, AlterReplicateConfig, AlterWAL act as global barriers: no other messages can be in flight on any PChannel.
• AlterResourceGroup, DropResourceGroup are serialized via ExclusiveCluster but are CChannel-only (no PChannel-level exclusive lock).