fix: add AllowSetupMetadataLockInstruments Compatible with MySQL 5.7 and previous versions

Author: dbking

go/base/context.go

@@ -247,7 +247,9 @@ type MigrationContext struct {
 
 	recentBinlogCoordinates mysql.BinlogCoordinates
 
-	BinlogSyncerMaxReconnectAttempts int
+	BinlogSyncerMaxReconnectAttempts  int
+	AllowSetupMetadataLockInstruments bool
+	IsOpenMetadataLockInstruments     bool
 
 	Log Logger
 }

go/cmd/gh-ost/main.go

@@ -137,6 +137,7 @@ func main() {
 	flag.Int64Var(&migrationContext.HooksStatusIntervalSec, "hooks-status-interval", 60, "how many seconds to wait between calling onStatus hook")
 
 	flag.UintVar(&migrationContext.ReplicaServerId, "replica-server-id", 99999, "server id used by gh-ost process. Default: 99999")
+	flag.BoolVar(&migrationContext.AllowSetupMetadataLockInstruments, "allow-setup-metadata-lock-instruments", false, "validate rename session hold the MDL of original table before unlock tables in cut-over phase")
 	flag.IntVar(&migrationContext.BinlogSyncerMaxReconnectAttempts, "binlogsyncer-max-reconnect-attempts", 0, "when master node fails, the maximum number of binlog synchronization attempts to reconnect. 0 is unlimited")
 
 	flag.BoolVar(&migrationContext.IncludeTriggers, "include-triggers", false, "When true, the triggers (if exist) will be created on the new table")

go/logic/applier.go

@@ -416,6 +416,28 @@ func (this *Applier) dropTable(tableName string) error {
 	return nil
 }
 
+func (this *Applier) StateMetadataLockInstrument() error {
+	query := `select /*+ MAX_EXECUTION_TIME(300) */ ENABLED, TIMED from performance_schema.setup_instruments WHERE NAME = 'wait/lock/metadata/sql/mdl'`
+	var enabled, timed string
+	if err := this.db.QueryRow(query).Scan(&enabled, &timed); err != nil {
+		return this.migrationContext.Log.Errorf("query performance_schema.setup_instruments with name wait/lock/metadata/sql/mdl error: %s", err)
+	}
+	if strings.EqualFold(enabled, "YES") && strings.EqualFold(timed, "YES") {
+		this.migrationContext.IsOpenMetadataLockInstruments = true
+		return nil
+	}
+	if !this.migrationContext.AllowSetupMetadataLockInstruments {
+		return nil
+	}
+	this.migrationContext.Log.Infof("instrument wait/lock/metadata/sql/mdl state: enabled %s, timed %s", enabled, timed)
+	if _, err := this.db.Exec(`UPDATE performance_schema.setup_instruments SET ENABLED = 'YES', TIMED = 'YES' WHERE NAME = 'wait/lock/metadata/sql/mdl'`); err != nil {
+		return this.migrationContext.Log.Errorf("enable instrument wait/lock/metadata/sql/mdl error: %s", err)
+	}
+	this.migrationContext.IsOpenMetadataLockInstruments = true
+	this.migrationContext.Log.Infof("instrument wait/lock/metadata/sql/mdl enabled")
+	return nil
+}
+
 // dropTriggers drop the triggers on the applied host
 func (this *Applier) DropTriggersFromGhost() error {
 	if len(this.migrationContext.Triggers) > 0 {
@@ -1192,7 +1214,7 @@ func (this *Applier) AtomicCutOverMagicLock(sessionIdChan chan int64, tableLocke
 
 	this.migrationContext.Log.Infof("Session renameLockSessionId is %+v", *renameLockSessionId)
 	// checking the lock holded by rename session
-	if *renameLockSessionId > 0 {
+	if *renameLockSessionId > 0 && this.migrationContext.IsOpenMetadataLockInstruments {
 		sleepDuration := time.Duration(10*this.migrationContext.CutOverLockTimeoutSeconds) * time.Millisecond
 		for i := 1; i <= 100; i++ {
 			err := this.ExpectMetadataLock(*renameLockSessionId)

go/logic/migrator.go

@@ -1205,6 +1205,10 @@ func (this *Migrator) initiateApplier() error {
 		}
 	}
 	this.applier.WriteChangelogState(string(GhostTableMigrated))
+	if err := this.applier.StateMetadataLockInstrument(); err != nil {
+		this.migrationContext.Log.Errorf("Unable to enable metadata lock instrument, see further error details. Bailing out")
+		return err
+	}
 	go this.applier.InitiateHeartbeat()
 	return nil
 }

go/logic/migrator_test.go

@@ -477,17 +477,18 @@ func (suite *MigratorTestSuite) TestCutOverLossDataCaseLockGhostBeforeRename() {
 		migrationContext.ThrottleHTTPTimeoutMillis = 1000
 		migrationContext.CutOverLockTimeoutSeconds = 4
 
-		//nolint:dogsled
 		_, filename, _, _ := runtime.Caller(0)
 		migrationContext.ServeSocketFile = filepath.Join(filepath.Dir(filename), "../../tmp/gh-ost.sock")
 		migrationContext.PostponeCutOverFlagFile = filepath.Join(filepath.Dir(filename), "../../tmp/ghost.postpone.flag")
 
 		migrator := NewMigrator(migrationContext, "0.0.0")
 
+		//nolint:contextcheck
 		done <- migrator.Migrate()
 	}()
 
 	time.Sleep(2 * time.Second)
+	//nolint:dogsled
 	_, filename, _, _ := runtime.Caller(0)
 	err = os.Remove(filepath.Join(filepath.Dir(filename), "../../tmp/ghost.postpone.flag"))
 	if err != nil {
@@ -528,7 +529,6 @@ func (suite *MigratorTestSuite) TestCutOverLossDataCaseLockGhostBeforeRename() {
 
 	suite.Require().Equal("testing", tableName)
 	suite.Require().Equal("CREATE TABLE `testing` (\n  `id` int NOT NULL,\n  `name` varchar(64) DEFAULT NULL,\n  `foobar` varchar(255) DEFAULT NULL,\n  PRIMARY KEY (`id`)\n) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci", createTableSQL)
-
 }
 
 func TestMigrator(t *testing.T) {