domain: splite handleDDLEvent into new thread (#53734) (#55277)

ref #53744

pkg/domain/domain.go

@@ -2277,6 +2277,9 @@ func (do *Domain) UpdateTableStatsLoop(ctx, initStatsCtx sessionctx.Context) err
 	// This is because the updated worker's primary responsibilities are to update the change delta and handle DDL operations.
 	// These tasks do not interfere with or depend on the initialization process.
 	do.wg.Run(func() { do.updateStatsWorker(ctx, owner) }, "updateStatsWorker")
+	do.wg.Run(func() {
+		do.handleDDLEvent()
+	}, "handleDDLEvent")
 	// Wait for the stats worker to finish the initialization.
 	// Otherwise, we may start the auto analyze worker before the stats cache is initialized.
 	do.wg.Run(
@@ -2481,12 +2484,6 @@ func (do *Domain) updateStatsWorker(ctx sessionctx.Context, owner owner.Manager)
 		case <-do.exit:
 			do.updateStatsWorkerExitPreprocessing(statsHandle, owner)
 			return
-			// This channel is sent only by ddl owner.
-		case t := <-statsHandle.DDLEventCh():
-			err := statsHandle.HandleDDLEvent(t)
-			if err != nil {
-				logutil.BgLogger().Error("handle ddl event failed", zap.String("event", t.String()), zap.Error(err))
-			}
 		case <-deltaUpdateTicker.C:
 			err := statsHandle.DumpStatsDeltaToKV(false)
 			if err != nil {
@@ -2512,6 +2509,24 @@ func (do *Domain) updateStatsWorker(ctx sessionctx.Context, owner owner.Manager)
 	}
 }
 
+func (do *Domain) handleDDLEvent() {
+	logutil.BgLogger().Info("handleDDLEvent started.")
+	defer util.Recover(metrics.LabelDomain, "handleDDLEvent", nil, false)
+	statsHandle := do.StatsHandle()
+	for {
+		select {
+		case <-do.exit:
+			return
+			// This channel is sent only by ddl owner.
+		case t := <-statsHandle.DDLEventCh():
+			err := statsHandle.HandleDDLEvent(t)
+			if err != nil {
+				logutil.BgLogger().Error("handle ddl event failed", zap.String("event", t.String()), zap.Error(err))
+			}
+		}
+	}
+}
+
 func (do *Domain) autoAnalyzeWorker(owner owner.Manager) {
 	defer util.Recover(metrics.LabelDomain, "autoAnalyzeWorker", nil, false)
 	statsHandle := do.StatsHandle()