processor: fix task status flushed too many before table is initializ…

…ed (#1190) #1191

cherry pick #1190 to release-4.0 (#1191)

cdc/model/owner.go

@@ -209,6 +209,8 @@ type TaskStatus struct {
 	Operation    map[TableID]*TableOperation   `json:"operation"`
 	AdminJobType AdminJobType                  `json:"admin-job-type"`
 	ModRevision  int64                         `json:"-"`
+	// true means Operation record has been changed
+	Dirty bool `json:"-"`
 }
 
 // String implements fmt.Stringer interface.

cdc/processor.go

@@ -210,6 +210,8 @@ func newProcessor(
 		schemaStorage: schemaStorage,
 		errCh:         errCh,
 
+		flushCheckpointInterval: flushCheckpointInterval,
+
 		position: &model.TaskPosition{CheckPointTs: checkpointTs},
 		output:   make(chan *model.PolymorphicEvent, defaultOutputChanSize),
 
@@ -534,11 +536,15 @@ func (p *processor) flushTaskStatusAndPosition(ctx context.Context) error {
 			if err != nil {
 				return false, backoff.Permanent(errors.Trace(err))
 			}
-			err = p.flushTaskPosition(ctx)
-			if err != nil {
-				return true, errors.Trace(err)
+			// processor reads latest task status from etcd, analyzes operation
+			// field and processes table add or delete. If operation is unapplied
+			// but stays unchanged after processor handling tables, it means no
+			// status is changed and we don't need to flush task status neigher.
+			if !taskStatus.Dirty {
+				return false, nil
 			}
-			return true, nil
+			err = p.flushTaskPosition(ctx)
+			return true, err
 		})
 	if err != nil {
 		// not need to check error
@@ -598,6 +604,7 @@ func (p *processor) handleTables(ctx context.Context, status *model.TaskStatus)
 					log.Warn("table which will be deleted is not found", zap.Int64("tableID", tableID))
 					opt.Done = true
 					opt.Status = model.OperFinished
+					status.Dirty = true
 					continue
 				}
 				stopped, checkpointTs := table.safeStop()
@@ -610,6 +617,7 @@ func (p *processor) handleTables(ctx context.Context, status *model.TaskStatus)
 						opt.Done = true
 						opt.Status = model.OperFinished
 					}
+					status.Dirty = true
 				}
 			}
 		} else {
@@ -622,6 +630,7 @@ func (p *processor) handleTables(ctx context.Context, status *model.TaskStatus)
 			}
 			p.addTable(ctx, tableID, replicaInfo)
 			opt.Status = model.OperProcessed
+			status.Dirty = true
 		}
 	}
 
@@ -639,13 +648,17 @@ func (p *processor) handleTables(ctx context.Context, status *model.TaskStatus)
 			}
 			status.Operation[tableID].Done = true
 			status.Operation[tableID].Status = model.OperFinished
+			status.Dirty = true
 		default:
 			goto done
 		}
 	}
 done:
 	if !status.SomeOperationsUnapplied() {
 		status.Operation = nil
+		// status.Dirty must be true when status changes from `unapplied` to `applied`,
+		// setting status.Dirty = true is not **must** here.
+		status.Dirty = true
 	}
 	return tablesToRemove, nil
 }