Slow webflux multipart upload

[sbxz]

Hello,

We are developing a document submission application using WebFlux. However, we have noticed that handling multipart requests is slower with WebFlux compared to MVC. For example, when using MultipartFile in MVC, sending a 200MB file takes about 700ms, whereas it takes 4.2s with WebFlux (FilePart) and 4.5s with PartEvent.

Did we miss something?

Here is a repository reproducing the issue: Repo

Spring boot version : 3.4.4
Java 21

[sdeleuze]

I suspected that when working in this area recently in #34178 and #34388 but was not 100% sure, but your report seems to confirm there is something to improve there, so I will try to have a deeper look.

What I saw was slow upload locally with big files, so I know how to reproduce even if for now, I am not sure about the reason.