schedule: placement rules cache reduce cache low usage fit

server/schedule/checker/checker_controller.go

@@ -18,6 +18,7 @@ import (
 	"context"
 	"time"
 
+	"github.com/pingcap/failpoint"
 	"github.com/tikv/pd/pkg/cache"
 	"github.com/tikv/pd/pkg/core"
 	"github.com/tikv/pd/pkg/errs"
@@ -91,13 +92,26 @@ func (c *Controller) CheckRegion(region *core.RegionInfo) []*operator.Operator {
 	}
 
 	if c.opts.IsPlacementRulesEnabled() {
-		fit := c.priorityInspector.Inspect(region)
-		if op := c.ruleChecker.CheckWithFit(region, fit); op != nil {
-			if opController.OperatorCount(operator.OpReplica) < c.opts.GetReplicaScheduleLimit() {
-				return []*operator.Operator{op}
+		skipRuleCheck := c.cluster.GetOpts().IsPlacementRulesCacheEnabled() &&
+			c.cluster.GetRuleManager().IsRegionFitCached(c.cluster, region)
+		if skipRuleCheck {
+			// If the fit is fetched from cache, it seems that the region doesn't need check
+			failpoint.Inject("assertShouldNotCache", func() {
+				panic("cached shouldn't be used")
+			})
+			ruleCheckerGetCacheCounter.Inc()
+		} else {
+			failpoint.Inject("assertShouldCache", func() {
+				panic("cached should be used")
+			})
+			fit := c.priorityInspector.Inspect(region)
+			if op := c.ruleChecker.CheckWithFit(region, fit); op != nil {
+				if opController.OperatorCount(operator.OpReplica) < c.opts.GetReplicaScheduleLimit() {
+					return []*operator.Operator{op}
+				}
+				operator.OperatorLimitCounter.WithLabelValues(c.ruleChecker.GetType(), operator.OpReplica.String()).Inc()
+				c.regionWaitingList.Put(region.GetID(), nil)
 			}
-			operator.OperatorLimitCounter.WithLabelValues(c.ruleChecker.GetType(), operator.OpReplica.String()).Inc()
-			c.regionWaitingList.Put(region.GetID(), nil)
 		}
 	} else {
 		if op := c.learnerChecker.Check(region); op != nil {

server/schedule/checker/rule_checker.go

@@ -20,7 +20,6 @@ import (
 	"math"
 	"time"
 
-	"github.com/pingcap/failpoint"
 	"github.com/pingcap/kvproto/pkg/metapb"
 	"github.com/pingcap/kvproto/pkg/pdpb"
 	"github.com/pingcap/log"
@@ -128,17 +127,6 @@ func (c *RuleChecker) CheckWithFit(region *core.RegionInfo, fit *placement.Regio
 		log.Debug("fail to check region", zap.Uint64("region-id", region.GetID()), zap.Error(errRegionNoLeader))
 		return
 	}
-	// If the fit is fetched from cache, it seems that the region doesn't need cache
-	if c.cluster.GetOpts().IsPlacementRulesCacheEnabled() && fit.IsCached() {
-		failpoint.Inject("assertShouldNotCache", func() {
-			panic("cached shouldn't be used")
-		})
-		ruleCheckerGetCacheCounter.Inc()
-		return nil
-	}
-	failpoint.Inject("assertShouldCache", func() {
-		panic("cached should be used")
-	})
 
 	// If the fit is calculated by FitRegion, which means we get a new fit result, thus we should
 	// invalid the cache if it exists

server/schedule/placement/fit.go

@@ -21,7 +21,6 @@ import (
 
 	"github.com/pingcap/kvproto/pkg/metapb"
 	"github.com/tikv/pd/pkg/core"
-	"github.com/tikv/pd/pkg/utils/syncutil"
 )
 
 const replicaBaseScore = 100
@@ -30,30 +29,12 @@ const replicaBaseScore = 100
 // All peers are divided into corresponding rules according to the matching
 // rules, and the remaining Peers are placed in the OrphanPeers list.
 type RegionFit struct {
-	mu struct {
-		syncutil.RWMutex
-		cached bool
-	}
 	RuleFits     []*RuleFit     `json:"rule-fits"`
 	OrphanPeers  []*metapb.Peer `json:"orphan-peers"`
 	regionStores []*core.StoreInfo
 	rules        []*Rule
 }
 
-// SetCached indicates this RegionFit is fetch form cache
-func (f *RegionFit) SetCached(cached bool) {
-	f.mu.Lock()
-	defer f.mu.Unlock()
-	f.mu.cached = cached
-}
-
-// IsCached indicates whether this result is fetched from caches
-func (f *RegionFit) IsCached() bool {
-	f.mu.RLock()
-	defer f.mu.RUnlock()
-	return f.mu.cached
-}
-
 // Replace return true if the replacement store is fit all constraints and isolation score is not less than the origin.
 func (f *RegionFit) Replace(srcStoreID uint64, dstStore *core.StoreInfo) bool {
 	fit := f.getRuleFitByStoreID(srcStoreID)

server/schedule/placement/fit_test.go

@@ -19,6 +19,7 @@ import (
 	"strconv"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/pingcap/kvproto/pkg/metapb"
 	"github.com/stretchr/testify/assert"
@@ -28,6 +29,7 @@ import (
 
 func makeStores() StoreSet {
 	stores := core.NewStoresInfo()
+	now := time.Now()
 	for zone := 1; zone <= 5; zone++ {
 		for rack := 1; rack <= 5; rack++ {
 			for host := 1; host <= 5; host++ {
@@ -42,7 +44,7 @@ func makeStores() StoreSet {
 					if x == 5 {
 						labels["engine"] = "tiflash"
 					}
-					stores.SetStore(core.NewStoreInfoWithLabel(id, labels))
+					stores.SetStore(core.NewStoreInfoWithLabel(id, labels).Clone(core.SetLastHeartbeatTS(now)))
 				}
 			}
 		}

server/schedule/placement/region_rule_cache.go

@@ -21,6 +21,10 @@ import (
 	"github.com/tikv/pd/pkg/utils/syncutil"
 )
 
+const (
+	minHitCountToCacheHit = 10 // RegionHit is cached only when the number of hits exceeds this
+)
+
 // RegionRuleFitCacheManager stores each region's RegionFit Result and involving variables
 // only when the RegionFit result is satisfied with its rules
 // RegionRuleFitCacheManager caches RegionFit result for each region only when:
@@ -65,7 +69,7 @@ func (manager *RegionRuleFitCacheManager) CheckAndGetCache(region *core.RegionIn
 	}
 	manager.mu.RLock()
 	defer manager.mu.RUnlock()
-	if cache, ok := manager.regionCaches[region.GetID()]; ok && cache.bestFit != nil {
+	if cache, ok := manager.regionCaches[region.GetID()]; ok {
 		if cache.IsUnchanged(region, rules, stores) {
 			return true, cache.bestFit
 		}
@@ -80,7 +84,13 @@ func (manager *RegionRuleFitCacheManager) SetCache(region *core.RegionInfo, fit
 	}
 	manager.mu.Lock()
 	defer manager.mu.Unlock()
-	fit.SetCached(true)
+	if cache, ok := manager.regionCaches[region.GetID()]; ok {
+		cache.hitCount++
+		if cache.hitCount >= minHitCountToCacheHit {
+			cache.bestFit = fit
+		}
+		return
+	}
 	manager.regionCaches[region.GetID()] = manager.toRegionRuleFitCache(region, fit)
 }
 
@@ -90,6 +100,7 @@ type regionRuleFitCache struct {
 	regionStores []*storeCache
 	rules        []ruleCache
 	bestFit      *RegionFit
+	hitCount     uint32
 }
 
 // IsUnchanged checks whether the region and rules unchanged for the cache
@@ -132,7 +143,8 @@ func (manager *RegionRuleFitCacheManager) toRegionRuleFitCache(region *core.Regi
 		region:       toRegionCache(region),
 		regionStores: manager.toStoreCacheList(fit.regionStores),
 		rules:        toRuleCacheList(fit.rules),
-		bestFit:      fit,
+		bestFit:      nil,
+		hitCount:     0,
 	}
 }
 

server/schedule/placement/rule_manager.go

@@ -325,18 +325,30 @@ func (m *RuleManager) GetRulesForApplyRange(start, end []byte) []*Rule {
 	return m.ruleList.getRulesForApplyRange(start, end)
 }
 
+// IsRegionFitCached returns whether the RegionFit can be cached.
+func (m *RuleManager) IsRegionFitCached(storeSet StoreSet, region *core.RegionInfo) bool {
+	regionStores := getStoresByRegion(storeSet, region)
+	rules := m.GetRulesForApplyRegion(region)
+	isCached, _ := m.cache.CheckAndGetCache(region, rules, regionStores)
+	return isCached
+}
+
 // FitRegion fits a region to the rules it matches.
-func (m *RuleManager) FitRegion(storeSet StoreSet, region *core.RegionInfo) *RegionFit {
+func (m *RuleManager) FitRegion(storeSet StoreSet, region *core.RegionInfo) (fit *RegionFit) {
 	regionStores := getStoresByRegion(storeSet, region)
 	rules := m.GetRulesForApplyRegion(region)
+	var isCached bool
 	if m.opt.IsPlacementRulesCacheEnabled() {
-		if ok, fit := m.cache.CheckAndGetCache(region, rules, regionStores); fit != nil && ok {
+		if isCached, fit = m.cache.CheckAndGetCache(region, rules, regionStores); isCached && fit != nil {
 			return fit
 		}
 	}
-	fit := fitRegion(regionStores, region, rules, m.opt.IsWitnessAllowed())
+	fit = fitRegion(regionStores, region, rules, m.opt.IsWitnessAllowed())
 	fit.regionStores = regionStores
 	fit.rules = rules
+	if isCached {
+		m.SetRegionFitCache(region, fit)
+	}
 	return fit
 }
 

server/schedule/placement/rule_manager_test.go

@@ -24,13 +24,14 @@ import (
 	"github.com/tikv/pd/pkg/core"
 	"github.com/tikv/pd/pkg/storage/endpoint"
 	"github.com/tikv/pd/pkg/storage/kv"
+	"github.com/tikv/pd/server/config"
 )
 
 func newTestManager(t *testing.T) (endpoint.RuleStorage, *RuleManager) {
 	re := require.New(t)
 	store := endpoint.NewStorageEndpoint(kv.NewMemoryKV(), nil)
 	var err error
-	manager := NewRuleManager(store, nil, nil)
+	manager := NewRuleManager(store, nil, config.NewTestOptions())
 	err = manager.Initialize(3, []string{"zone", "rack", "host"})
 	re.NoError(err)
 	return store, manager
@@ -421,6 +422,49 @@ func TestCheckApplyRules(t *testing.T) {
 	re.Regexp("needs at least one leader or voter", err.Error())
 }
 
+func TestCacheManager(t *testing.T) {
+	re := require.New(t)
+	_, manager := newTestManager(t)
+	manager.opt.SetPlacementRulesCacheEnabled(true)
+	rules := addExtraRules(0)
+	re.NoError(manager.SetRules(rules))
+	stores := makeStores()
+
+	regionMeta := &metapb.Region{
+		Id:          1,
+		StartKey:    []byte(""),
+		EndKey:      []byte(""),
+		RegionEpoch: &metapb.RegionEpoch{ConfVer: 0, Version: 0},
+		Peers: []*metapb.Peer{
+			{Id: 11, StoreId: 1111, Role: metapb.PeerRole_Voter},
+			{Id: 12, StoreId: 2111, Role: metapb.PeerRole_Voter},
+			{Id: 13, StoreId: 3111, Role: metapb.PeerRole_Voter},
+		},
+	}
+	region := core.NewRegionInfo(regionMeta, regionMeta.Peers[0])
+	fit := manager.FitRegion(stores, region)
+	manager.SetRegionFitCache(region, fit)
+	// bestFit is not stored when the total number of hits is insufficient.
+	for i := 1; i < minHitCountToCacheHit/2; i++ {
+		manager.FitRegion(stores, region)
+		re.True(manager.IsRegionFitCached(stores, region))
+		cache := manager.cache.regionCaches[1]
+		re.Equal(uint32(i), cache.hitCount)
+		re.Nil(cache.bestFit)
+	}
+	// Store bestFit when the total number of hits is sufficient.
+	for i := 0; i < minHitCountToCacheHit; i++ {
+		manager.FitRegion(stores, region)
+	}
+	cache := manager.cache.regionCaches[1]
+	re.Equal(uint32(minHitCountToCacheHit), cache.hitCount)
+	re.NotNil(cache.bestFit)
+	// Cache invalidation after change
+	regionMeta.Peers[2] = &metapb.Peer{Id: 14, StoreId: 4111, Role: metapb.PeerRole_Voter}
+	region = core.NewRegionInfo(regionMeta, regionMeta.Peers[0])
+	re.False(manager.IsRegionFitCached(stores, region))
+}
+
 func dhex(hk string) []byte {
 	k, err := hex.DecodeString(hk)
 	if err != nil {