backport-2.1: storage: make load-based replica rebalancing decisions at the store level

docs/generated/settings/settings.html

@@ -17,9 +17,9 @@
 <tr><td><code>jobs.registry.leniency</code></td><td>duration</td><td><code>1m0s</code></td><td>the amount of time to defer any attempts to reschedule a job</td></tr>
 <tr><td><code>kv.allocator.lease_rebalancing_aggressiveness</code></td><td>float</td><td><code>1</code></td><td>set greater than 1.0 to rebalance leases toward load more aggressively, or between 0 and 1.0 to be more conservative about rebalancing leases</td></tr>
 <tr><td><code>kv.allocator.load_based_lease_rebalancing.enabled</code></td><td>boolean</td><td><code>true</code></td><td>set to enable rebalancing of range leases based on load and latency</td></tr>
+<tr><td><code>kv.allocator.load_based_rebalancing</code></td><td>enumeration</td><td><code>1</code></td><td>whether to rebalance based on the distribution of QPS across stores [off = 0, leases = 1, leases and replicas = 2]</td></tr>
+<tr><td><code>kv.allocator.qps_rebalance_threshold</code></td><td>float</td><td><code>0.25</code></td><td>minimum fraction away from the mean a store's QPS (such as queries per second) can be before it is considered overfull or underfull</td></tr>
 <tr><td><code>kv.allocator.range_rebalance_threshold</code></td><td>float</td><td><code>0.05</code></td><td>minimum fraction away from the mean a store's range count can be before it is considered overfull or underfull</td></tr>
-<tr><td><code>kv.allocator.stat_based_rebalancing.enabled</code></td><td>boolean</td><td><code>false</code></td><td>set to enable rebalancing range replicas and leases to more evenly distribute read and write load across the stores in a cluster</td></tr>
-<tr><td><code>kv.allocator.stat_rebalance_threshold</code></td><td>float</td><td><code>0.2</code></td><td>minimum fraction away from the mean a store's stats (like disk usage or writes per second) can be before it is considered overfull or underfull</td></tr>
 <tr><td><code>kv.bulk_io_write.concurrent_export_requests</code></td><td>integer</td><td><code>5</code></td><td>number of export requests a store will handle concurrently before queuing</td></tr>
 <tr><td><code>kv.bulk_io_write.concurrent_import_requests</code></td><td>integer</td><td><code>1</code></td><td>number of import requests a store will handle concurrently before queuing</td></tr>
 <tr><td><code>kv.bulk_io_write.max_rate</code></td><td>byte size</td><td><code>8.0 EiB</code></td><td>the rate limit (bytes/sec) to use for writes to disk on behalf of bulk io ops</td></tr>

pkg/cmd/roachtest/rebalance_load.go

@@ -107,20 +107,30 @@ func registerRebalanceLoad(r *registry) {
 		}
 	}
 
-	minutes := 2 * time.Minute
-	numNodes := 4 // the last node is just used to generate load
 	concurrency := 128
 
 	r.Add(testSpec{
 		Name:   `rebalance-leases-by-load`,
-		Nodes:  nodes(numNodes),
-		Stable: false, // TODO(a-robinson): Promote to stable
+		Nodes:  nodes(4), // the last node is just used to generate load
+		Stable: false,    // TODO(a-robinson): Promote to stable
 		Run: func(ctx context.Context, t *test, c *cluster) {
 			if local {
 				concurrency = 32
 				fmt.Printf("lowering concurrency to %d in local testing\n", concurrency)
 			}
-			rebalanceLoadRun(ctx, t, c, minutes, concurrency)
+			rebalanceLoadRun(ctx, t, c, 2*time.Minute, concurrency)
+		},
+	})
+	r.Add(testSpec{
+		Name:   `rebalance-replicas-by-load`,
+		Nodes:  nodes(7), // the last node is just used to generate load
+		Stable: false,    // TODO(a-robinson): Promote to stable
+		Run: func(ctx context.Context, t *test, c *cluster) {
+			if local {
+				concurrency = 32
+				fmt.Printf("lowering concurrency to %d in local testing\n", concurrency)
+			}
+			rebalanceLoadRun(ctx, t, c, 5*time.Minute, concurrency)
 		},
 	})
 }

pkg/settings/registry.go

@@ -34,10 +34,13 @@ var Registry = make(map[string]Setting)
 // When a setting is removed, it should be added to this list so that we cannot
 // accidentally reuse its name, potentially mis-handling older values.
 var retiredSettings = map[string]struct{}{
-	//removed as of 2.0.
+	// removed as of 2.0.
 	"kv.gc.batch_size":                     {},
 	"kv.transaction.max_intents":           {},
 	"diagnostics.reporting.report_metrics": {},
+	// removed as of 2.1.
+	"kv.allocator.stat_based_rebalancing.enabled": {},
+	"kv.allocator.stat_rebalance_threshold":       {},
 }
 
 // Register adds a setting to the registry.

pkg/storage/allocator.go

@@ -90,10 +90,6 @@ var leaseRebalancingAggressiveness = settings.RegisterNonNegativeFloatSetting(
 	1.0,
 )
 
-func statsBasedRebalancingEnabled(st *cluster.Settings, disableStatsBasedRebalance bool) bool {
-	return EnableStatsBasedRebalancing.Get(&st.SV) && st.Version.IsActive(cluster.VersionStatsBasedRebalancing) && !disableStatsBasedRebalance
-}
-
 // AllocatorAction enumerates the various replication adjustments that may be
 // recommended by the allocator.
 type AllocatorAction int
@@ -247,10 +243,7 @@ func MakeAllocator(
 // supplied range, as governed by the supplied zone configuration. It
 // returns the required action that should be taken and a priority.
 func (a *Allocator) ComputeAction(
-	ctx context.Context,
-	zone config.ZoneConfig,
-	rangeInfo RangeInfo,
-	disableStatsBasedRebalancing bool,
+	ctx context.Context, zone config.ZoneConfig, rangeInfo RangeInfo,
 ) (AllocatorAction, float64) {
 	if a.storePool == nil {
 		// Do nothing if storePool is nil for some unittests.
@@ -341,10 +334,8 @@ func (a *Allocator) ComputeAction(
 }
 
 type decisionDetails struct {
-	Target               string
-	Existing             string  `json:",omitempty"`
-	RangeBytes           int64   `json:",omitempty"`
-	RangeWritesPerSecond float64 `json:",omitempty"`
+	Target   string
+	Existing string `json:",omitempty"`
 }
 
 // AllocateTarget returns a suitable store for a new allocation with the
@@ -357,42 +348,54 @@ func (a *Allocator) AllocateTarget(
 	zone config.ZoneConfig,
 	existing []roachpb.ReplicaDescriptor,
 	rangeInfo RangeInfo,
-	disableStatsBasedRebalancing bool,
 ) (*roachpb.StoreDescriptor, string, error) {
 	sl, aliveStoreCount, throttledStoreCount := a.storePool.getStoreList(rangeInfo.Desc.RangeID, storeFilterThrottled)
 
+	target, details := a.allocateTargetFromList(
+		ctx, sl, zone, existing, rangeInfo, a.scorerOptions())
+
+	if target != nil {
+		return target, details, nil
+	}
+
+	// When there are throttled stores that do match, we shouldn't send
+	// the replica to purgatory.
+	if throttledStoreCount > 0 {
+		return nil, "", errors.Errorf("%d matching stores are currently throttled", throttledStoreCount)
+	}
+	return nil, "", &allocatorError{
+		constraints:      zone.Constraints,
+		existingReplicas: len(existing),
+		aliveStores:      aliveStoreCount,
+		throttledStores:  throttledStoreCount,
+	}
+}
+
+func (a *Allocator) allocateTargetFromList(
+	ctx context.Context,
+	sl StoreList,
+	zone config.ZoneConfig,
+	existing []roachpb.ReplicaDescriptor,
+	rangeInfo RangeInfo,
+	options scorerOptions,
+) (*roachpb.StoreDescriptor, string) {
 	analyzedConstraints := analyzeConstraints(
 		ctx, a.storePool.getStoreDescriptor, existing, zone)
-	options := a.scorerOptions(disableStatsBasedRebalancing)
 	candidates := allocateCandidates(
 		sl, analyzedConstraints, existing, rangeInfo, a.storePool.getLocalities(existing), options,
 	)
 	log.VEventf(ctx, 3, "allocate candidates: %s", candidates)
 	if target := candidates.selectGood(a.randGen); target != nil {
 		log.VEventf(ctx, 3, "add target: %s", target)
 		details := decisionDetails{Target: target.compactString(options)}
-		if options.statsBasedRebalancingEnabled {
-			details.RangeBytes = rangeInfo.LogicalBytes
-			details.RangeWritesPerSecond = rangeInfo.WritesPerSecond
-		}
 		detailsBytes, err := json.Marshal(details)
 		if err != nil {
 			log.Warningf(ctx, "failed to marshal details for choosing allocate target: %s", err)
 		}
-		return &target.store, string(detailsBytes), nil
+		return &target.store, string(detailsBytes)
 	}
 
-	// When there are throttled stores that do match, we shouldn't send
-	// the replica to purgatory.
-	if throttledStoreCount > 0 {
-		return nil, "", errors.Errorf("%d matching stores are currently throttled", throttledStoreCount)
-	}
-	return nil, "", &allocatorError{
-		constraints:      zone.Constraints,
-		existingReplicas: len(existing),
-		aliveStores:      aliveStoreCount,
-		throttledStores:  throttledStoreCount,
-	}
+	return nil, ""
 }
 
 func (a Allocator) simulateRemoveTarget(
@@ -401,7 +404,6 @@ func (a Allocator) simulateRemoveTarget(
 	zone config.ZoneConfig,
 	candidates []roachpb.ReplicaDescriptor,
 	rangeInfo RangeInfo,
-	disableStatsBasedRebalancing bool,
 ) (roachpb.ReplicaDescriptor, string, error) {
 	// Update statistics first
 	// TODO(a-robinson): This could theoretically interfere with decisions made by other goroutines,
@@ -413,7 +415,7 @@ func (a Allocator) simulateRemoveTarget(
 		a.storePool.updateLocalStoreAfterRebalance(targetStore, rangeInfo, roachpb.REMOVE_REPLICA)
 	}()
 	log.VEventf(ctx, 3, "simulating which replica would be removed after adding s%d", targetStore)
-	return a.RemoveTarget(ctx, zone, candidates, rangeInfo, disableStatsBasedRebalancing)
+	return a.RemoveTarget(ctx, zone, candidates, rangeInfo)
 }
 
 // RemoveTarget returns a suitable replica to remove from the provided replica
@@ -426,7 +428,6 @@ func (a Allocator) RemoveTarget(
 	zone config.ZoneConfig,
 	candidates []roachpb.ReplicaDescriptor,
 	rangeInfo RangeInfo,
-	disableStatsBasedRebalancing bool,
 ) (roachpb.ReplicaDescriptor, string, error) {
 	if len(candidates) == 0 {
 		return roachpb.ReplicaDescriptor{}, "", errors.Errorf("must supply at least one candidate replica to allocator.RemoveTarget()")
@@ -441,7 +442,7 @@ func (a Allocator) RemoveTarget(
 
 	analyzedConstraints := analyzeConstraints(
 		ctx, a.storePool.getStoreDescriptor, rangeInfo.Desc.Replicas, zone)
-	options := a.scorerOptions(disableStatsBasedRebalancing)
+	options := a.scorerOptions()
 	rankedCandidates := removeCandidates(
 		sl,
 		analyzedConstraints,
@@ -455,10 +456,6 @@ func (a Allocator) RemoveTarget(
 			if exist.StoreID == bad.store.StoreID {
 				log.VEventf(ctx, 3, "remove target: %s", bad)
 				details := decisionDetails{Target: bad.compactString(options)}
-				if options.statsBasedRebalancingEnabled {
-					details.RangeBytes = rangeInfo.LogicalBytes
-					details.RangeWritesPerSecond = rangeInfo.WritesPerSecond
-				}
 				detailsBytes, err := json.Marshal(details)
 				if err != nil {
 					log.Warningf(ctx, "failed to marshal details for choosing remove target: %s", err)
@@ -495,7 +492,6 @@ func (a Allocator) RebalanceTarget(
 	raftStatus *raft.Status,
 	rangeInfo RangeInfo,
 	filter storeFilter,
-	disableStatsBasedRebalancing bool,
 ) (*roachpb.StoreDescriptor, string) {
 	sl, _, _ := a.storePool.getStoreList(rangeInfo.Desc.RangeID, filter)
 
@@ -529,7 +525,7 @@ func (a Allocator) RebalanceTarget(
 
 	analyzedConstraints := analyzeConstraints(
 		ctx, a.storePool.getStoreDescriptor, rangeInfo.Desc.Replicas, zone)
-	options := a.scorerOptions(disableStatsBasedRebalancing)
+	options := a.scorerOptions()
 	results := rebalanceCandidates(
 		ctx,
 		sl,
@@ -585,8 +581,7 @@ func (a Allocator) RebalanceTarget(
 			target.store.StoreID,
 			zone,
 			replicaCandidates,
-			rangeInfo,
-			disableStatsBasedRebalancing)
+			rangeInfo)
 		if err != nil {
 			log.Warningf(ctx, "simulating RemoveTarget failed: %s", err)
 			return nil, ""
@@ -606,10 +601,6 @@ func (a Allocator) RebalanceTarget(
 		Target:   target.compactString(options),
 		Existing: existingCandidates.compactString(options),
 	}
-	if options.statsBasedRebalancingEnabled {
-		details.RangeBytes = rangeInfo.LogicalBytes
-		details.RangeWritesPerSecond = rangeInfo.WritesPerSecond
-	}
 	detailsBytes, err := json.Marshal(details)
 	if err != nil {
 		log.Warningf(ctx, "failed to marshal details for choosing rebalance target: %s", err)
@@ -618,12 +609,10 @@ func (a Allocator) RebalanceTarget(
 	return &target.store, string(detailsBytes)
 }
 
-func (a *Allocator) scorerOptions(disableStatsBasedRebalancing bool) scorerOptions {
+func (a *Allocator) scorerOptions() scorerOptions {
 	return scorerOptions{
-		deterministic:                a.storePool.deterministic,
-		statsBasedRebalancingEnabled: statsBasedRebalancingEnabled(a.storePool.st, disableStatsBasedRebalancing),
-		rangeRebalanceThreshold:      rangeRebalanceThreshold.Get(&a.storePool.st.SV),
-		statRebalanceThreshold:       statRebalanceThreshold.Get(&a.storePool.st.SV),
+		deterministic:           a.storePool.deterministic,
+		rangeRebalanceThreshold: rangeRebalanceThreshold.Get(&a.storePool.st.SV),
 	}
 }