Don't unconditionally send consumer snapshot when becoming leader (#4965

)

Feasibly a Raft node that is keeping up with its peers can become a
leader regardless of whether or not the upper layer is caught up with
its applies. Since the leader change notification to the upper state
machine could interleave with the apply queue, then unconditionally
sending a snapshot as a new append entry on consumer leader transitions
could cause the rest of the group to revert to an earlier consumer
state.

Signed-off-by: Neil Twigg <neil@nats.io>

server/jetstream_cluster.go

@@ -4660,16 +4660,6 @@ func (js *jetStream) monitorConsumer(o *consumer, ca *consumerAssignment) {
 				js.setConsumerAssignmentRecovering(ca)
 			}
 
-			// Synchronize everyone to our state.
-			if isLeader && n != nil {
-				// Only send out if we have state.
-				if _, _, applied := n.Progress(); applied > 0 {
-					if snap, err := o.store.EncodedState(); err == nil {
-						n.SendSnapshot(snap)
-					}
-				}
-			}
-
 			// Process the change.
 			if err := js.processConsumerLeaderChange(o, isLeader); err == nil && isLeader {
 				doSnapshot(true)