Merge pull request #174 from Wattpad/test-on-replica-manual-replicati…

…on-control

outstanding. Thank you!

go/base/context.go

@@ -83,13 +83,14 @@ type MigrationContext struct {
 	ServeSocketFile string
 	ServeTCPPort    int64
 
-	Noop                    bool
-	TestOnReplica           bool
-	MigrateOnReplica        bool
-	OkToDropTable           bool
-	InitiallyDropOldTable   bool
-	InitiallyDropGhostTable bool
-	CutOverType             CutOver
+	Noop                         bool
+	TestOnReplica                bool
+	MigrateOnReplica             bool
+	TestOnReplicaSkipReplicaStop bool
+	OkToDropTable                bool
+	InitiallyDropOldTable        bool
+	InitiallyDropGhostTable      bool
+	CutOverType                  CutOver
 
 	TableEngine               string
 	RowsEstimate              int64

go/cmd/gh-ost/main.go

@@ -61,6 +61,7 @@ func main() {
 
 	executeFlag := flag.Bool("execute", false, "actually execute the alter & migrate the table. Default is noop: do some tests and exit")
 	flag.BoolVar(&migrationContext.TestOnReplica, "test-on-replica", false, "Have the migration run on a replica, not on the master. At the end of migration replication is stopped, and tables are swapped and immediately swap-revert. Replication remains stopped and you can compare the two tables for building trust")
+	flag.BoolVar(&migrationContext.TestOnReplicaSkipReplicaStop, "test-on-replica-skip-replica-stop", false, "When --test-on-replica is enabled, do not issue commands stop replication (requires --test-on-replica)")
 	flag.BoolVar(&migrationContext.MigrateOnReplica, "migrate-on-replica", false, "Have the migration run on a replica, not on the master. This will do the full migration on the replica including cut-over (as opposed to --test-on-replica)")
 
 	flag.BoolVar(&migrationContext.OkToDropTable, "ok-to-drop-table", false, "Shall the tool drop the old table at end of operation. DROPping tables can be a long locking operation, which is why I'm not doing it by default. I'm an online tool, yes?")
@@ -149,6 +150,13 @@ func main() {
 	if migrationContext.SwitchToRowBinlogFormat && migrationContext.AssumeRBR {
 		log.Fatalf("--switch-to-rbr and --assume-rbr are mutually exclusive")
 	}
+	if migrationContext.TestOnReplicaSkipReplicaStop {
+		if !migrationContext.TestOnReplica {
+			log.Fatalf("--test-on-replica-skip-replica-stop requires --test-on-replica to be enabled")
+		}
+		log.Warning("--test-on-replica-skip-replica-stop enabled. We will not stop replication before cut-over. Ensure you have a plugin that does this.")
+	}
+
 	switch *cutOver {
 	case "atomic", "default", "":
 		migrationContext.CutOverType = base.CutOverAtomic

go/logic/applier.go

@@ -574,6 +574,7 @@ func (this *Applier) StopReplication() error {
 	if err := this.StopSlaveSQLThread(); err != nil {
 		return err
 	}
+
 	readBinlogCoordinates, executeBinlogCoordinates, err := mysql.GetReplicationBinlogCoordinates(this.db)
 	if err != nil {
 		return err

go/logic/migrator.go

@@ -478,9 +478,14 @@ func (this *Migrator) cutOver() (err error) {
 		// the same cut-over phase as the master would use. That means we take locks
 		// and swap the tables.
 		// The difference is that we will later swap the tables back.
-		log.Debugf("testing on replica. Stopping replication IO thread")
-		if err := this.retryOperation(this.applier.StopReplication); err != nil {
-			return err
+
+		if this.migrationContext.TestOnReplicaSkipReplicaStop {
+			log.Warningf("--test-on-replica-skip-replica-stop enabled, we are not stopping replication.")
+		} else {
+			log.Debugf("testing on replica. Stopping replication IO thread")
+			if err := this.retryOperation(this.applier.StopReplication); err != nil {
+				return err
+			}
 		}
 		// We're merly testing, we don't want to keep this state. Rollback the renames as possible
 		defer this.applier.RenameTablesRollback()