add comments

cdc/owner/changefeed.go

@@ -415,7 +415,7 @@ func (c *changefeed) tick(ctx cdcContext.Context, captures map[model.CaptureID]*
 	// be max uint64. In this case, we need to advance newResolvedTs to global barrier
 	// ts and advance newCheckpointTs to min table barrier ts.
 	if newResolvedTs == math.MaxUint64 || newCheckpointTs == math.MaxUint64 {
-		if newCheckpointTs != math.MaxUint64 || newResolvedTs != math.MaxUint64 {
+		if newCheckpointTs != newResolvedTs {
 			log.Panic("newResolvedTs and newCheckpointTs should be both max uint64 or not",
 				zap.Uint64("checkpointTs", preCheckpointTs),
 				zap.Uint64("resolvedTs", c.state.Status.ResolvedTs),
@@ -426,8 +426,6 @@ func (c *changefeed) tick(ctx cdcContext.Context, captures map[model.CaptureID]*
 		newCheckpointTs = barrier.minDDLBarrierTs
 	}
 
-	// If the table pipeline corresponding to minDDLBarrierTs is not ready, newCheckpointTs
-	// should wait for it.
 	// Note that newResolvedTs could be larger than barrier.GlobalBarrierTs no matter
 	// whether redo is enabled.
 	if newCheckpointTs > barrier.minDDLBarrierTs {
@@ -459,6 +457,9 @@ func (c *changefeed) tick(ctx cdcContext.Context, captures map[model.CaptureID]*
 		} else {
 			newResolvedTs = prevResolvedTs
 		}
+		// If allPhysicalTables is empty, newCheckpointTs would advance to min table barrier ts, which may be larger
+		// than preResolvedTs. In this case, we need to set newCheckpointTs to preResolvedTs to guarantee that the
+		// checkpointTs will not cross the preResolvedTs.
 		if newCheckpointTs > prevResolvedTs {
 			newCheckpointTs = prevResolvedTs
 			if newCheckpointTs < preCheckpointTs {