code: func (builder *RequestBuilder) SetChecksumRequest(checksum *tipb.ChecksumRequest) *RequestBuilder {
  	if builder.err != nil {
  		return builder
  	}
  
  	builder.Request.Tp = kv.ReqTypeChecksum
  	builder.Request.StartTs = checksum.StartTs
  	builder.Request.Data, builder.err = checksum.Marshal()
  	builder.Request.NotFillCache = true
  	return builder
  }
docs: // SetChecksumRequest sets the request type to "ReqTypeChecksum" and construct request data.