code: func (builder *RequestBuilder) SetMemTracker(sctx sessionctx.Context, label fmt.Stringer) *RequestBuilder {
  	t := memory.NewTracker(label, sctx.GetSessionVars().MemQuotaDistSQL)
  	t.AttachTo(sctx.GetSessionVars().StmtCtx.MemTracker)
  	builder.Request.MemTracker = t
  	return builder
  }
docs: // SetMemTracker sets a memTracker for this request.