kvserver: never pause local replica

As observed in cockroachdb#84884, an overloaded store that held leases could end up
"pausing" replication traffic to itself. This (likely) had no practical
effect since the leader never sends messages to itself, but it meant
reporting bogus counts of paused replicas.

This commit ensures that a raft leader will never pause itself.

Release note: None

pkg/kv/kvserver/replica_raft_overload.go

@@ -43,6 +43,7 @@ var pauseReplicationIOThreshold = settings.RegisterFloatSetting(
 )
 
 type computeExpendableOverloadedFollowersInput struct {
+	self      roachpb.ReplicaID
 	replDescs roachpb.ReplicaSet
 	// TODO(tbg): all entries are overloaded, so consdier removing the IOThreshold here
 	// because it's confusing.
@@ -104,11 +105,10 @@ func computeExpendableOverloadedFollowers(
 	var nonLive map[roachpb.ReplicaID]nonLiveReason
 	var liveOverloadedVoterCandidates map[roachpb.ReplicaID]struct{}
 	var liveOverloadedNonVoterCandidates map[roachpb.ReplicaID]struct{}
-
 	var prs map[uint64]tracker.Progress
 
 	for _, replDesc := range d.replDescs.AsProto() {
-		if _, overloaded := d.ioOverloadMap[replDesc.StoreID]; !overloaded {
+		if _, overloaded := d.ioOverloadMap[replDesc.StoreID]; !overloaded || replDesc.ReplicaID == d.self {
 			continue
 		}
 		// There's at least one overloaded follower, so initialize
@@ -252,6 +252,7 @@ func (r *Replica) updatePausedFollowersLocked(
 	seed := int64(r.RangeID)
 	now := r.store.Clock().Now().GoTime()
 	d := computeExpendableOverloadedFollowersInput{
+		self:          r.replicaID,
 		replDescs:     r.descRLocked().Replicas(),
 		ioOverloadMap: ioOverloadMap,
 		getProgressMap: func(_ context.Context) map[uint64]tracker.Progress {

pkg/kv/kvserver/replica_raft_overload_test.go

@@ -46,6 +46,7 @@ func TestReplicaRaftOverload_computeExpendableOverloadedFollowers(t *testing.T)
 			require.Equal(t, "run", d.Cmd)
 			var seed uint64
 			var replDescs roachpb.ReplicaSet
+			var self roachpb.ReplicaID
 			ioOverloadMap := map[roachpb.StoreID]*admissionpb.IOThreshold{}
 			snapshotMap := map[roachpb.ReplicaID]struct{}{}
 			downMap := map[roachpb.ReplicaID]struct{}{}
@@ -65,6 +66,8 @@ func TestReplicaRaftOverload_computeExpendableOverloadedFollowers(t *testing.T)
 					switch arg.Key {
 					case "min-live-match-index":
 						minLiveMatchIndex = id
+					case "self":
+						self = roachpb.ReplicaID(id)
 					case "voters", "learners":
 						replicaID := roachpb.ReplicaID(id)
 						if matchS != "" {
@@ -134,6 +137,7 @@ func TestReplicaRaftOverload_computeExpendableOverloadedFollowers(t *testing.T)
 			}
 
 			m, _ := computeExpendableOverloadedFollowers(ctx, computeExpendableOverloadedFollowersInput{
+				self:              self,
 				replDescs:         replDescs,
 				ioOverloadMap:     ioOverloadMap,
 				getProgressMap:    getProgressMap,

pkg/kv/kvserver/testdata/replica_raft_overload/self.txt

@@ -0,0 +1,4 @@
+# Won't consider itself for pausing.
+run voters=(1,2,3) overloaded=(1) self=1
+----
+[]