testutils,kvserver: disable store rebalancer when replication manual

`ReplicationManual` can be specified in tests which use a test cluster
to prevent lease/replica movements.

This proves vital if the test is asserting exactly on the placement of a
range, or its leaseholder.

Also disable the store rebalancer, which could move both leases and
replicas under `ReplicationManual` before.

Informs: #132310
Informs: #132272
Release note: None

pkg/kv/kvserver/store_rebalancer.go

@@ -149,6 +149,7 @@ type StoreRebalancer struct {
 	processTimeoutFn        func(replica CandidateReplica) time.Duration
 	objectiveProvider       RebalanceObjectiveProvider
 	subscribedToSpanConfigs func() bool
+	disabled                func() bool
 }
 
 // NewStoreRebalancer creates a StoreRebalancer to work in tandem with the
@@ -191,6 +192,10 @@ func NewStoreRebalancer(
 			}
 			return !rq.store.cfg.SpanConfigSubscriber.LastUpdated().IsEmpty()
 		},
+		disabled: func() bool {
+			return LoadBasedRebalancingMode.Get(&st.SV) == LBRebalancingOff ||
+				rq.store.cfg.TestingKnobs.DisableStoreRebalancer
+		},
 	}
 	sr.AddLogTag("store-rebalancer", nil)
 	rq.store.metrics.registry.AddMetricStruct(&sr.metrics)
@@ -308,15 +313,13 @@ func (sr *StoreRebalancer) Start(ctx context.Context, stopper *stop.Stopper) {
 				timer.Read = true
 				timer.Reset(jitteredInterval(allocator.LoadBasedRebalanceInterval.Get(&sr.st.SV)))
 			}
-
+			if sr.disabled() {
+				continue
+			}
 			// Once the rebalance mode and rebalance objective are defined for
 			// this loop, they are immutable and do not change. This avoids
 			// inconsistency where the rebalance objective changes and very
 			// different or contradicting actions are then taken.
-			mode := sr.RebalanceMode()
-			if mode == LBRebalancingOff {
-				continue
-			}
 			if !sr.subscribedToSpanConfigs() {
 				continue
 			}
@@ -326,7 +329,7 @@ func (sr *StoreRebalancer) Start(ctx context.Context, stopper *stop.Stopper) {
 
 			hottestRanges := sr.replicaRankings.TopLoad(objective.ToDimension())
 			options := sr.scorerOptions(ctx, objective.ToDimension())
-			rctx := sr.NewRebalanceContext(ctx, options, hottestRanges, mode)
+			rctx := sr.NewRebalanceContext(ctx, options, hottestRanges, sr.RebalanceMode())
 			sr.rebalanceStore(ctx, rctx)
 		}
 	})

pkg/kv/kvserver/testing_knobs.go

@@ -176,6 +176,9 @@ type StoreTestingKnobs struct {
 	DisableReplicaGCQueue bool
 	// DisableReplicateQueue disables the replication queue.
 	DisableReplicateQueue bool
+	// DisableStoreRebalancer turns off the store rebalancer which moves replicas
+	// and leases.
+	DisableStoreRebalancer bool
 	// DisableLoadBasedSplitting turns off LBS so no splits happen because of load.
 	DisableLoadBasedSplitting bool
 	// LoadBasedSplittingOverrideKey returns a key which should be used for load

pkg/testutils/testcluster/testcluster.go

@@ -581,6 +581,7 @@ func (tc *TestCluster) AddServer(
 		stkCopy.DisableSplitQueue = true
 		stkCopy.DisableMergeQueue = true
 		stkCopy.DisableReplicateQueue = true
+		stkCopy.DisableStoreRebalancer = true
 		serverArgs.Knobs.Store = &stkCopy
 	}