vitessio/vitess · error

no rpl_semi_sync_replica_status variable in mysql

Error message

no rpl_semi_sync_replica_status variable in mysql

What it means

SemiSyncReplicationStatus runs a SHOW query for rpl_semi_sync_replica_status and requires exactly one row. If the row is missing, the semi-sync plugin is not loaded (so the variable doesn't exist), and this error is returned with false. It is the replica-side counterpart of ErrNoSemiSync handling.

Source

Thrown at go/vt/mysqlctl/replication.go:1322

	case mysql.SemiSyncTypeMaster:
		primary = vars["Rpl_semi_sync_master_status"] == "ON"
		replica = vars["Rpl_semi_sync_slave_status"] == "ON"
	}
	return primary, replica
}

// SemiSyncReplicationStatus returns whether semi-sync is currently used by replication.
func (mysqld *Mysqld) SemiSyncReplicationStatus(ctx context.Context) (bool, error) {
	query, err := mysqld.semiSyncReplicationStatusQuery(ctx)
	if err != nil {
		return false, err
	}
	qr, err := mysqld.FetchSuperQuery(ctx, query)
	if err != nil {
		return false, err
	}
	if len(qr.Rows) != 1 {
		return false, errors.New("no rpl_semi_sync_replica_status variable in mysql")
	}
	if qr.Rows[0][1].ToString() == "ON" {
		return true, nil
	}
	return false, nil
}

// SemiSyncExtensionLoaded returns whether semi-sync plugins are loaded.
func (mysqld *Mysqld) SemiSyncExtensionLoaded(ctx context.Context) (mysql.SemiSyncType, error) {
	conn, connErr := getPoolReconnect(ctx, mysqld.dbaPool)
	if connErr != nil {
		return mysql.SemiSyncTypeUnknown, connErr
	}
	defer conn.Recycle()

	return conn.Conn.SemiSyncExtensionLoaded()
}

View on GitHub (pinned to 01a25a7d17)

Solutions

1. Install and enable the semi-sync replica plugin: INSTALL PLUGIN rpl_semi_sync_replica SONAME 'semisync_replica.so'; SET GLOBAL rpl_semi_sync_replica_enabled=ON.
2. Use SemiSyncExtensionLoaded/SemiSyncType to detect plugin absence first and skip the status check.
3. On older MySQL (<8.0.26), the variable is rpl_semi_sync_slave_status — match the query to the server version.
4. Handle the error as 'semi-sync inactive' rather than fatal if semi-sync is optional in your deployment.

loaded, _ := mysqld.SemiSyncExtensionLoaded(ctx)
if !loaded {
    // plugin not installed; SemiSyncReplicationStatus would fail
    return
}

func isSemiSyncMissing(err error) bool {
    return errors.Is(err, mysqlctl.ErrNoSemiSync) || strings.Contains(err.Error(), "rpl_semi_sync_replica_status")
}

on, err := mysqld.SemiSyncReplicationStatus(ctx)
if err != nil {
    if strings.Contains(err.Error(), "rpl_semi_sync_replica_status") {
        log.Warn("semi-sync replica plugin not loaded; semi-sync inactive")
        return nil
    }
    return vterrors.Wrapf(err, "semi-sync replica status")
}

When it happens

Trigger: Calling Mysqld.SemiSyncReplicationStatus when the query for rpl_semi_sync_replica_status returns len(qr.Rows) != 1 — the semi-sync plugin isn't installed, so MySQL has no such status variable.

Common situations: Checking semi-sync status on a replica where semisync_slave.so was never installed; MySQL version mismatch where the replica uses newer source/replica naming (rpl_semi_sync_replica_status missing on older servers expecting rpl_semi_sync_slave_status); plugin load failures at mysqld startup.

Related errors

• ErrNoSemiSync
• Last_SQL_Error: ${LastSQL_Error}, Last_IO_Error: ${LastIO_Er
• GetPreviousGTIDs: previous GTIDs not found
• startPos.GTIDSet is wrong type - expected filePosGTID, got:
• failed to set @source_binlog_checksum=@@global.binlog_checks

AI-assisted analysis of vitessio/vitess@01a25a7d17 (2026-09-01). Data as JSON: /api/errors/047bacc522d7bc51. Report an issue: GitHub.