optimize migrator's executeWriteFuncs

go/logic/migrator.go

@@ -1279,32 +1279,39 @@ func (this *Migrator) executeWriteFuncs() error {
 					return err
 				}
 			}
-		default:
+		case copyRowsFunc := <-this.copyRowsQueue:
+			if err := this.drainApplierEventQueue(); err != nil {
+				return this.migrationContext.Log.Errore(err)
+			}
 			{
-				select {
-				case copyRowsFunc := <-this.copyRowsQueue:
-					{
-						copyRowsStartTime := time.Now()
-						// Retries are handled within the copyRowsFunc
-						if err := copyRowsFunc(); err != nil {
-							return this.migrationContext.Log.Errore(err)
-						}
-						if niceRatio := this.migrationContext.GetNiceRatio(); niceRatio > 0 {
-							copyRowsDuration := time.Since(copyRowsStartTime)
-							sleepTimeNanosecondFloat64 := niceRatio * float64(copyRowsDuration.Nanoseconds())
-							sleepTime := time.Duration(int64(sleepTimeNanosecondFloat64)) * time.Nanosecond
-							time.Sleep(sleepTime)
-						}
-					}
-				default:
-					{
-						// Hmmmmm... nothing in the queue; no events, but also no row copy.
-						// This is possible upon load. Let's just sleep it over.
-						this.migrationContext.Log.Debugf("Getting nothing in the write queue. Sleeping...")
-						time.Sleep(time.Second)
-					}
+				copyRowsStartTime := time.Now()
+				// Retries are handled within the copyRowsFunc
+				if err := copyRowsFunc(); err != nil {
+					return this.migrationContext.Log.Errore(err)
+				}
+				if niceRatio := this.migrationContext.GetNiceRatio(); niceRatio > 0 {
+					copyRowsDuration := time.Since(copyRowsStartTime)
+					sleepTimeNanosecondFloat64 := niceRatio * float64(copyRowsDuration.Nanoseconds())
+					sleepTime := time.Duration(sleepTimeNanosecondFloat64) * time.Nanosecond
+					time.Sleep(sleepTime)
+				}
+			}
+		}
+	}
+}
+
+func (this *Migrator) drainApplierEventQueue() error {
+	for {
+		select {
+		case eventStruct := <-this.applyEventsQueue:
+			{
+				this.throttler.throttle(nil)
+				if err := this.onApplyEventStruct(eventStruct); err != nil {
+					return err
 				}
 			}
+		default:
+			return nil
 		}
 	}
 }