fix: allow run gh-ost when performance_schema off & can custom z name to prevent issue github#1536 - github#1536

Author: Nam Nguyen

go/base/context.go

@@ -260,6 +260,9 @@ type MigrationContext struct {
 	AllowSetupMetadataLockInstruments bool
 	IsOpenMetadataLockInstruments     bool
 
+	AllowDisabledMetadataLockInstruments bool
+	CustomZLength                        int
+
 	Log Logger
 }
 
@@ -341,12 +344,12 @@ func (this *MigrationContext) SetConnectionCharset(charset string) {
 }
 
 func getSafeTableName(baseName string, suffix string) string {
-	name := fmt.Sprintf("_%s_%s", baseName, suffix)
+	name := fmt.Sprintf("%s_%s_%s", getCustomZ(), baseName, suffix)
 	if len(name) <= mysql.MaxTableNameLength {
 		return name
 	}
 	extraCharacters := len(name) - mysql.MaxTableNameLength
-	return fmt.Sprintf("_%s_%s", baseName[0:len(baseName)-extraCharacters], suffix)
+	return fmt.Sprintf("%s_%s_%s", getCustomZ(), baseName[0:len(baseName)-extraCharacters], suffix)
 }
 
 // GetGhostTableName generates the name of ghost table, based on original table name

go/base/zname.go

@@ -0,0 +1,11 @@
+package base
+
+import "strings"
+
+var (
+	CustomZLength int
+)
+
+func getCustomZ() string {
+	return strings.Repeat("z", CustomZLength)
+}

go/cmd/gh-ost/main.go

@@ -143,6 +143,9 @@ func main() {
 	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.AllowDisabledMetadataLockInstruments, "allow-disabled-metadata-lock-instruments", false, "allow disabled metadata lock instruments")
+	flag.IntVar(&migrationContext.CustomZLength, "custom-z-length", 0, "custom z name length")
+
 	flag.BoolVar(&migrationContext.IncludeTriggers, "include-triggers", false, "When true, the triggers (if exist) will be created on the new table")
 	flag.StringVar(&migrationContext.TriggerSuffix, "trigger-suffix", "", "Add a suffix to the trigger name (i.e '_v2'). Requires '--include-triggers'")
 	flag.BoolVar(&migrationContext.RemoveTriggerSuffix, "remove-trigger-suffix-if-exists", false, "Remove given suffix from name of trigger. Requires '--include-triggers' and '--trigger-suffix'")
@@ -373,6 +376,10 @@ func main() {
 		migrationContext.Log.Errore(err)
 	}
 
+	if migrationContext.CustomZLength > 0 {
+		base.CustomZLength = migrationContext.CustomZLength
+	}
+
 	log.Infof("starting gh-ost %+v (git commit: %s)", AppVersion, GitCommit)
 	acceptSignals(migrationContext)
 

go/logic/applier.go

@@ -545,7 +545,24 @@ func (this *Applier) dropTable(tableName string) error {
 }
 
 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'`
+	// Check if performance_schema is enabled first
+	var performanceSchemaValue string
+	query := `SHOW VARIABLES LIKE 'performance_schema'`
+	if err := this.db.QueryRow(query).Scan(new(string), &performanceSchemaValue); err != nil {
+		return this.migrationContext.Log.Errorf("Unable to determine performance_schema status: %s", err)
+	}
+
+	if !strings.EqualFold(performanceSchemaValue, "ON") {
+		this.migrationContext.Log.Warningf("performance_schema is disabled (value: %s)", performanceSchemaValue)
+		if this.migrationContext.AllowDisabledMetadataLockInstruments {
+			this.migrationContext.Log.Warningf("AllowDisabledMetadataLockInstruments is enabled, proceeding without metadata lock instrumentation")
+			this.migrationContext.IsOpenMetadataLockInstruments = false
+			return nil
+		}
+		return this.migrationContext.Log.Errorf("performance_schema is disabled. Please enable it or use --allow-disabled-metadata-lock-instruments to proceed without metadata lock checking")
+	}
+
+	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)