kv/client: use ephemeral goroutine to handle region range request

cdc/kv/client.go

@@ -601,10 +601,17 @@ func (s *eventFeedSession) eventFeed(ctx context.Context, ts uint64) error {
 				return ctx.Err()
 			case task := <-s.requestRangeCh:
 				s.rangeChSizeGauge.Dec()
-				err := s.divideAndSendEventFeedToRegions(ctx, task.span, task.ts)
-				if err != nil {
-					return errors.Trace(err)
-				}
+				// divideAndSendEventFeedToRegions could be block for some time,
+				// since it must wait for the region lock available. In order to
+				// consume region range request from `requestRangeCh` as soon as
+				// possible, we create a new goroutine to handle it.
+				// The sequence of region range we process is not matter, the
+				// region lock keeps the region access sequence.
+				// Besides the count or frequency of range request is limitted,
+				// we use ephemeral goroutine instead of permanent gourotine.
+				g.Go(func() error {
+					return s.divideAndSendEventFeedToRegions(ctx, task.span, task.ts)
+				})
 			}
 		}
 	})
@@ -672,6 +679,25 @@ func (s *eventFeedSession) scheduleRegionRequest(ctx context.Context, sri single
 	}
 
 	res := s.rangeLock.LockRange(ctx, sri.span.Start, sri.span.End, sri.verID.GetID(), sri.verID.GetVer())
+	failpoint.Inject("kvClientMockRangeLock", func(val failpoint.Value) {
+		// short sleep to wait region has split
+		time.Sleep(time.Second)
+		s.rangeLock.UnlockRange(sri.span.Start, sri.span.End, sri.verID.GetID(), sri.verID.GetVer(), sri.ts)
+		regionNum := val.(int)
+		retryRanges := make([]regionspan.ComparableSpan, 0, regionNum)
+		start := []byte("a")
+		end := []byte("b1001")
+		for i := 0; i < regionNum; i++ {
+			span := regionspan.Span{Start: start, End: end}
+			retryRanges = append(retryRanges, regionspan.ToComparableSpan(span))
+			start = end
+			end = []byte(fmt.Sprintf("b%d", 1002+i))
+		}
+		res = regionspan.LockRangeResult{
+			Status:      regionspan.LockRangeStatusStale,
+			RetryRanges: retryRanges,
+		}
+	})
 
 	if res.Status == regionspan.LockRangeStatusWait {
 		res = res.WaitFn()

cdc/kv/client_test.go

@@ -15,6 +15,7 @@ package kv
 
 import (
 	"context"
+	"fmt"
 	"net"
 	"sync"
 	"sync/atomic"
@@ -3053,3 +3054,122 @@ func (s *etcdSuite) TestKVClientForceReconnect2(c *check.C) {
 
 	cancel()
 }
+
+// TestConcurrentProcessRangeRequest when region range request channel is full,
+// the kv client can process it correctly without deadlock. This is more likely
+// to happen when region split and merge frequently and large stale requests exist.
+func (s *etcdSuite) TestConcurrentProcessRangeRequest(c *check.C) {
+	defer testleak.AfterTest(c)()
+	defer s.TearDownTest(c)
+	ctx, cancel := context.WithCancel(context.Background())
+	wg := &sync.WaitGroup{}
+
+	requestIDs := new(sync.Map)
+	ch1 := make(chan *cdcpb.ChangeDataEvent, 10)
+	srv1 := newMockChangeDataService(c, ch1)
+	srv1.recvLoop = func(server cdcpb.ChangeData_EventFeedServer) {
+		for {
+			req, err := server.Recv()
+			if err != nil {
+				return
+			}
+			requestIDs.Store(req.RegionId, req.RequestId)
+		}
+	}
+	server1, addr1 := newMockService(ctx, c, srv1, wg)
+
+	defer func() {
+		close(ch1)
+		server1.Stop()
+		wg.Wait()
+	}()
+
+	rpcClient, cluster, pdClient, err := mocktikv.NewTiKVAndPDClient("", mockcopr.NewCoprRPCHandler())
+	c.Assert(err, check.IsNil)
+	pdClient = &mockPDClient{Client: pdClient, versionGen: defaultVersionGen}
+	tiStore, err := tikv.NewTestTiKVStore(rpcClient, pdClient, nil, nil, 0)
+	c.Assert(err, check.IsNil)
+	kvStorage := newStorageWithCurVersionCache(tiStore, addr1)
+	defer kvStorage.Close() //nolint:errcheck
+
+	storeID := uint64(1)
+	regionID := uint64(1000)
+	peerID := regionID + 1
+	cluster.AddStore(storeID, addr1)
+	cluster.Bootstrap(regionID, []uint64{storeID}, []uint64{peerID}, peerID)
+
+	err = failpoint.Enable("github.com/pingcap/ticdc/cdc/kv/kvClientMockRangeLock", "1*return(20)")
+	c.Assert(err, check.IsNil)
+	defer func() {
+		_ = failpoint.Disable("github.com/pingcap/ticdc/cdc/kv/kvClientMockRangeLock")
+	}()
+	lockresolver := txnutil.NewLockerResolver(kvStorage)
+	isPullInit := &mockPullerInit{}
+	cdcClient := NewCDCClient(ctx, pdClient, kvStorage, &security.Credential{})
+	eventCh := make(chan *model.RegionFeedEvent, 10)
+	wg.Add(1)
+	go func() {
+		err := cdcClient.EventFeed(ctx, regionspan.ComparableSpan{Start: []byte("a"), End: []byte("z")}, 100, false, lockresolver, isPullInit, eventCh)
+		c.Assert(errors.Cause(err), check.Equals, context.Canceled)
+		cdcClient.Close() //nolint:errcheck
+		wg.Done()
+	}()
+
+	// the kv client is blocked by failpoint injection, and after region has split
+	// into more sub regions, the kv client will continue to handle and will find
+	// stale region requests (which is also caused by failpoint injection).
+	regionNum := 20
+	for i := 1; i < regionNum; i++ {
+		regionID := uint64(i + 1000)
+		peerID := regionID + 1
+		// split regions to [min, b1001), [b1001, b1002), ... [bN, max)
+		cluster.SplitRaw(regionID-1, regionID, []byte(fmt.Sprintf("b%d", regionID)), []uint64{peerID}, peerID)
+	}
+
+	// wait for all regions requested from cdc kv client
+	err = retry.Run(time.Millisecond*200, 20, func() error {
+		count := 0
+		requestIDs.Range(func(_, _ interface{}) bool {
+			count++
+			return true
+		})
+		if count == regionNum {
+			return nil
+		}
+		return errors.Errorf("region number %d is not as expected %d", count, regionNum)
+	})
+	c.Assert(err, check.IsNil)
+
+	// send initialized event and a resolved ts event to each region
+	requestIDs.Range(func(key, value interface{}) bool {
+		regionID := key.(uint64)
+		requestID := value.(uint64)
+		initialized := mockInitializedEvent(regionID, requestID)
+		ch1 <- initialized
+		resolved := &cdcpb.ChangeDataEvent{Events: []*cdcpb.Event{
+			{
+				RegionId:  regionID,
+				RequestId: requestID,
+				Event:     &cdcpb.Event_ResolvedTs{ResolvedTs: 120},
+			},
+		}}
+		ch1 <- resolved
+		return true
+	})
+
+	resolvedCount := 0
+checkEvent:
+	for {
+		select {
+		case <-eventCh:
+			resolvedCount++
+			if resolvedCount == regionNum*2 {
+				break checkEvent
+			}
+		case <-time.After(time.Second):
+			c.Errorf("no more events received")
+		}
+	}
+
+	cancel()
+}