checkpoint(dm): check outdated should respect snapshot create time

dm/syncer/checkpoint.go

@@ -280,12 +280,9 @@ type CheckPoint interface {
 	// corresponding to to Meta.Pos and gtid
 	FlushedGlobalPoint() binlog.Location
 
-	// CheckGlobalPoint checks whether we should save global checkpoint
-	// corresponding to Meta.Check
-	CheckGlobalPoint() bool
-
-	// CheckLastSnapshotCreationTime checks whether we should async flush checkpoint since last time async flush
-	CheckLastSnapshotCreationTime() bool
+	// LastFlushOutdated checks the start time of a flush (when call Snapshot) and finish time of a flush, if both of
+	// the two times are outdated, LastFlushOutdated returns true.
+	LastFlushOutdated() bool
 
 	// Rollback rolls global checkpoint and all table checkpoints back to flushed checkpoints
 	Rollback(schemaTracker *schema.Tracker)
@@ -878,18 +875,18 @@ func (cp *RemoteCheckPoint) String() string {
 	return cp.globalPoint.String()
 }
 
-// CheckGlobalPoint implements CheckPoint.CheckGlobalPoint.
-func (cp *RemoteCheckPoint) CheckGlobalPoint() bool {
+// LastFlushOutdated implements CheckPoint.LastFlushOutdated.
+func (cp *RemoteCheckPoint) LastFlushOutdated() bool {
 	cp.RLock()
 	defer cp.RUnlock()
-	return time.Since(cp.globalPointSaveTime) >= time.Duration(cp.cfg.CheckpointFlushInterval)*time.Second
-}
 
-// CheckLastSnapshotCreationTime implements CheckPoint.CheckLastSnapshotCreationTime.
-func (cp *RemoteCheckPoint) CheckLastSnapshotCreationTime() bool {
-	cp.RLock()
-	defer cp.RUnlock()
-	return time.Since(cp.lastSnapshotCreationTime) >= time.Duration(cp.cfg.CheckpointFlushInterval)*time.Second
+	if time.Since(cp.globalPointSaveTime) < time.Duration(cp.cfg.CheckpointFlushInterval)*time.Second {
+		return false
+	}
+	if time.Since(cp.lastSnapshotCreationTime) < time.Duration(cp.cfg.CheckpointFlushInterval)*time.Second {
+		return false
+	}
+	return true
 }
 
 // Rollback implements CheckPoint.Rollback.

dm/syncer/checkpoint_test.go

@@ -21,6 +21,7 @@ import (
 	"path/filepath"
 	"strings"
 	"testing"
+	"time"
 
 	tidbddl "github.com/pingcap/tidb/ddl"
 	"github.com/pingcap/tidb/parser/ast"
@@ -549,3 +550,18 @@ func TestRemoteCheckPointLoadIntoSchemaTracker(t *testing.T) {
 	_, err = schemaTracker.GetTableInfo(tbl2)
 	require.Error(t, err)
 }
+
+func TestLastFlushOutdated(t *testing.T) {
+	cfg := genDefaultSubTaskConfig4Test()
+	cfg.WorkerCount = 0
+	cfg.CheckpointFlushInterval = 1
+
+	cp := NewRemoteCheckPoint(tcontext.Background(), cfg, "1")
+	checkpoint := cp.(*RemoteCheckPoint)
+	checkpoint.globalPointSaveTime = time.Now().Add(-2 * time.Second)
+
+	require.True(t, checkpoint.LastFlushOutdated())
+	require.Nil(t, checkpoint.Snapshot(true))
+	// though snapshot is nil, checkpoint is not outdated
+	require.False(t, checkpoint.LastFlushOutdated())
+}

dm/syncer/syncer.go

@@ -987,9 +987,9 @@ func (s *Syncer) addJob(job *job) {
 	}
 }
 
-// checkShouldFlush checks whether syncer should flush now because last flushing is outdated.
-func (s *Syncer) checkShouldFlush() error {
-	if !s.checkpoint.CheckGlobalPoint() || !s.checkpoint.CheckLastSnapshotCreationTime() {
+// flushIfOutdated checks whether syncer should flush now because last flushing is outdated.
+func (s *Syncer) flushIfOutdated() error {
+	if !s.checkpoint.LastFlushOutdated() {
 		return nil
 	}
 
@@ -1011,7 +1011,7 @@ func (s *Syncer) handleJob(job *job) (added2Queue bool, err error) {
 	skipCheckFlush := false
 	defer func() {
 		if !skipCheckFlush && err == nil {
-			err = s.checkShouldFlush()
+			err = s.flushIfOutdated()
 		}
 	}()
 
@@ -1140,7 +1140,7 @@ func (s *Syncer) resetShardingGroup(table *filter.Table) {
 // and except rejecting to flush the checkpoint, we also need to rollback the checkpoint saved before
 // this should be handled when `s.Run` returned
 //
-// we may need to refactor the concurrency model to make the work-flow more clearer later.
+// we may need to refactor the concurrency model to make the work-flow more clear later.
 func (s *Syncer) flushCheckPoints() error {
 	err := s.execError.Load()
 	// TODO: for now, if any error occurred (including user canceled), checkpoint won't be updated. But if we have put
@@ -2162,7 +2162,7 @@ func (s *Syncer) Run(ctx context.Context) (err error) {
 		case *replication.GenericEvent:
 			if e.Header.EventType == replication.HEARTBEAT_EVENT {
 				// flush checkpoint even if there are no real binlog events
-				if s.checkpoint.CheckGlobalPoint() {
+				if s.checkpoint.LastFlushOutdated() {
 					s.tctx.L().Info("meet heartbeat event and then flush jobs")
 					err2 = s.flushJobs()
 				}
@@ -2480,7 +2480,7 @@ func (s *Syncer) handleRowsEvent(ev *replication.RowsEvent, ec eventContext) err
 		}
 	})
 
-	return s.checkShouldFlush()
+	return s.flushIfOutdated()
 }
 
 type queryEventContext struct {