dropping _osc (changelog) table at end of operation; also better status hint at end of operation

Author: Shlomi Noach

go/logic/migrator.go

@@ -335,6 +335,9 @@ func (this *Migrator) Migrate() (err error) {
 		return err
 	}
 
+	if err := this.finalCleanup(); err != nil {
+		return nil
+	}
 	log.Infof("Done migrating %s.%s", sql.EscapeName(this.migrationContext.DatabaseName), sql.EscapeName(this.migrationContext.OriginalTableName))
 	return nil
 }
@@ -381,26 +384,10 @@ func (this *Migrator) stopWritesAndCompleteMigration() (err error) {
 			}); err != nil {
 			return err
 		}
-		if err := this.dropOldTableIfRequired(); err != nil {
-			return err
-		}
 	}
 	return
 }
 
-func (this *Migrator) dropOldTableIfRequired() (err error) {
-	if !this.migrationContext.OkToDropTable {
-		return nil
-	}
-	dropTableFunc := func() error {
-		return this.applier.dropTable(this.migrationContext.GetOldTableName())
-	}
-	if err := this.retryOperation(dropTableFunc); err != nil {
-		return err
-	}
-	return nil
-}
-
 // Inject the "AllEventsUpToLockProcessed" state hint, wait for it to appear in the binary logs,
 // make sure the queue is drained.
 func (this *Migrator) waitForEventsUpToLock() (err error) {
@@ -435,9 +422,6 @@ func (this *Migrator) stopWritesAndCompleteMigrationOnMasterQuickAndBumpy() (err
 	if err := this.retryOperation(this.applier.UnlockTables); err != nil {
 		return err
 	}
-	if err := this.dropOldTableIfRequired(); err != nil {
-		return err
-	}
 
 	lockAndRenameDuration := this.migrationContext.RenameTablesEndTime.Sub(this.migrationContext.LockTablesStartTime)
 	renameDuration := this.migrationContext.RenameTablesEndTime.Sub(this.migrationContext.RenameTablesStartTime)
@@ -520,6 +504,7 @@ func (this *Migrator) stopWritesAndCompleteMigrationOnReplica() (err error) {
 
 	this.waitForEventsUpToLock()
 
+	this.printMigrationStatusHint()
 	log.Info("Table duplicated with new schema. Am not touching the original table. Replication is stopped. You may now compare the two tables to gain trust into this tool's operation")
 	return nil
 }
@@ -569,6 +554,17 @@ func (this *Migrator) initiateStatus() error {
 	return nil
 }
 
+func (this *Migrator) printMigrationStatusHint() {
+	hint := fmt.Sprintf("# Migrating %s.%s; Ghost table is %s.%s; migration started at %+v",
+		sql.EscapeName(this.migrationContext.DatabaseName),
+		sql.EscapeName(this.migrationContext.OriginalTableName),
+		sql.EscapeName(this.migrationContext.DatabaseName),
+		sql.EscapeName(this.migrationContext.GetGhostTableName()),
+		this.migrationContext.StartTime.Format(time.RubyDate),
+	)
+	fmt.Println(hint)
+}
+
 func (this *Migrator) printStatus() {
 	elapsedTime := this.migrationContext.ElapsedTime()
 	elapsedSeconds := int64(elapsedTime.Seconds())
@@ -580,16 +576,9 @@ func (this *Migrator) printStatus() {
 	}
 
 	// Before status, let's see if we should print a nice reminder for what exactly we're doing here.
-	shouldPrintCourtesyReminder := (elapsedSeconds%600 == 0)
-	if shouldPrintCourtesyReminder {
-		courtesyReminder := fmt.Sprintf("# Migrating %s.%s; Ghost table is %s.%s; migration started at %+v",
-			sql.EscapeName(this.migrationContext.DatabaseName),
-			sql.EscapeName(this.migrationContext.OriginalTableName),
-			sql.EscapeName(this.migrationContext.DatabaseName),
-			sql.EscapeName(this.migrationContext.GetGhostTableName()),
-			this.migrationContext.StartTime.Format(time.RubyDate),
-		)
-		fmt.Println(courtesyReminder)
+	shouldPrintMigrationStatusHint := (elapsedSeconds%600 == 0)
+	if shouldPrintMigrationStatusHint {
+		this.printMigrationStatusHint()
 	}
 
 	var etaSeconds float64 = math.MaxFloat64
@@ -816,3 +805,20 @@ func (this *Migrator) executeWriteFuncs() error {
 	}
 	return nil
 }
+
+// finalCleanup takes actions at very end of migration, dropping tables etc.
+func (this *Migrator) finalCleanup() error {
+	if err := this.retryOperation(this.applier.DropChangelogTable); err != nil {
+		return err
+	}
+	if this.migrationContext.OkToDropTable && !this.migrationContext.TestOnReplica {
+		dropTableFunc := func() error {
+			return this.applier.dropTable(this.migrationContext.GetOldTableName())
+		}
+		if err := this.retryOperation(dropTableFunc); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}