code: func (e *SelectLockExec) Open(ctx context.Context) error {
  	if err := e.baseExecutor.Open(ctx); err != nil {
  		return err
  	}
  
  	txnCtx := e.ctx.GetSessionVars().TxnCtx
  	txnCtx.ForUpdate = true
  	for id := range e.Schema().TblID2Handle {
  		// This operation is only for schema validator check.
  		txnCtx.UpdateDeltaForTable(id, 0, 0, map[int64]int64{})
  	}
  	return nil
  }
docs: // Open implements the Executor Open interface.