Large POSTs through Apache mod_proxy to mongrel failing

[Clifford Heath]

I have an Apache2 server working nicely with mod_proxy pointing at
mongrel that's started using --prefix. One of my forms allows file
upload, with the expectation of large files. When I upload a file of
370KB (from Firefox on Mac OS/X), Apache is returning a connection
reset error and dropping this in error.log:

Connection reset by peer: proxy: prefetch request body failed to
localhost from AAA.BBB.CCC.DDD

I checked the Apache source code, and there seems to be a 16384 byte
buffer which it uses to try to prefetch the POST body so it can send
Content-Length. After googling a bit, I tried setting some Apache2
special environment variables that promised to modify the behaviors:

SetEnv downgrade-1.0
SetEnv proxy-sendcl
SetEnv proxy-sendchunked

I tried these one at a time... still get the error.

What am I doing wrong?

Clifford Heath.

[Clifford Heath]

Does no-one have an answer for this?
Surely other people are uploading large files through Apache mod_proxy?
Can you share anything that looks relevant about your Apache config
please? I'm really stuck here...