code: func (ds *DataSource) PredicatePushDown(predicates []expression.Expression) ([]expression.Expression, LogicalPlan) {
  	ds.allConds = predicates
  	_, ds.pushedDownConds, predicates = expression.ExpressionsToPB(ds.ctx.GetSessionVars().StmtCtx, predicates, ds.ctx.GetClient())
  	return predicates, ds
  }
docs: // PredicatePushDown implements LogicalPlan PredicatePushDown interface.