gc_worker: reduce GC scan locks when meeting region cache miss (#18385)

store/tikv/gcworker/gc_worker.go

@@ -48,14 +48,18 @@ import (
 
 // GCWorker periodically triggers GC process on tikv server.
 type GCWorker struct {
-	uuid        string
-	desc        string
-	store       tikv.Storage
-	pdClient    pd.Client
-	gcIsRunning bool
-	lastFinish  time.Time
-	cancel      context.CancelFunc
-	done        chan error
+	uuid         string
+	desc         string
+	store        tikv.Storage
+	pdClient     pd.Client
+	gcIsRunning  bool
+	lastFinish   time.Time
+	cancel       context.CancelFunc
+	done         chan error
+	testingKnobs struct {
+		scanLocks    func(key []byte) []*tikv.Lock
+		resolveLocks func(regionID tikv.RegionVerID) (ok bool, err error)
+	}
 }
 
 // NewGCWorker creates a GCWorker instance.
@@ -870,6 +874,7 @@ func (w *GCWorker) resolveLocksForRange(
 		ctx = context.WithValue(ctx, "injectedBackoff", struct{}{})
 		bo = tikv.NewBackoffer(ctx, sleep)
 	})
+retryScanAndResolve:
 	for {
 		select {
 		case <-ctx.Done():
@@ -910,16 +915,33 @@ func (w *GCWorker) resolveLocksForRange(
 			locks[i] = tikv.NewLock(locksInfo[i])
 		}
 
-		ok, err1 := w.store.GetLockResolver().BatchResolveLocks(bo, locks, loc.Region)
-		if err1 != nil {
-			return regions, errors.Trace(err1)
+		if w.testingKnobs.scanLocks != nil {
+			locks = append(locks, w.testingKnobs.scanLocks(key)...)
 		}
-		if !ok {
-			err = bo.Backoff(tikv.BoTxnLock, errors.Errorf("remain locks: %d", len(locks)))
-			if err != nil {
-				return regions, errors.Trace(err)
+		for {
+			ok, err1 := w.store.GetLockResolver().BatchResolveLocks(bo, locks, loc.Region)
+			if w.testingKnobs.resolveLocks != nil {
+				ok, err1 = w.testingKnobs.resolveLocks(loc.Region)
 			}
-			continue
+			if err1 != nil {
+				return regions, errors.Trace(err1)
+			}
+			if !ok {
+				err = bo.Backoff(tikv.BoTxnLock, errors.Errorf("remain locks: %d", len(locks)))
+				if err != nil {
+					return regions, errors.Trace(err)
+				}
+				stillInSame, refreshedLoc, err := w.tryRelocateLocksRegion(bo, locks)
+				if err != nil {
+					return regions, errors.Trace(err)
+				}
+				if stillInSame {
+					loc = refreshedLoc
+					continue
+				}
+				continue retryScanAndResolve
+			}
+			break
 		}
 		if len(locks) < gcScanLockLimit {
 			regions++
@@ -945,6 +967,18 @@ func (w *GCWorker) resolveLocksForRange(
 	return regions, nil
 }
 
+func (w *GCWorker) tryRelocateLocksRegion(bo *tikv.Backoffer, locks []*tikv.Lock) (stillInSameRegion bool, refreshedLoc *tikv.KeyLocation, err error) {
+	if len(locks) == 0 {
+		return
+	}
+	refreshedLoc, err = w.store.GetRegionCache().LocateKey(bo, locks[0].Key)
+	if err != nil {
+		return
+	}
+	stillInSameRegion = refreshedLoc.Contains(locks[len(locks)-1].Key)
+	return
+}
+
 func (w *GCWorker) uploadSafePointToPD(ctx context.Context, safePoint uint64) error {
 	var newSafePoint uint64
 	var err error

store/tikv/gcworker/gc_worker_test.go

@@ -370,6 +370,39 @@ func (s *testGCWorkerSuite) TestResolveLockRangeInfine(c *C) {
 	c.Assert(err, NotNil)
 }
 
+func (s *testGCWorkerSuite) TestResolveLockRangeMeetRegionCacheMiss(c *C) {
+	var (
+		scanCnt       int
+		scanCntRef    = &scanCnt
+		resolveCnt    int
+		resolveCntRef = &resolveCnt
+	)
+	s.gcWorker.testingKnobs.scanLocks = func(key []byte) []*tikv.Lock {
+		*scanCntRef++
+		return []*tikv.Lock{
+			{
+				Key: []byte{1},
+			},
+			{
+				Key: []byte{1},
+			},
+		}
+	}
+	s.gcWorker.testingKnobs.resolveLocks = func(regionID tikv.RegionVerID) (ok bool, err error) {
+		*resolveCntRef++
+		if *resolveCntRef == 1 {
+			s.gcWorker.store.GetRegionCache().InvalidateCachedRegion(regionID)
+			// mock the region cache miss error
+			return false, nil
+		}
+		return true, nil
+	}
+	_, err := s.gcWorker.resolveLocksForRange(context.Background(), 1, []byte{0}, []byte{10})
+	c.Assert(err, IsNil)
+	c.Assert(resolveCnt, Equals, 2)
+	c.Assert(scanCnt, Equals, 1)
+}
+
 func (s *testGCWorkerSuite) TestRunGCJob(c *C) {
 	gcSafePointCacheInterval = 0
 	err := RunGCJob(context.Background(), s.store, 0, "mock", 1)