Hi,

Thanks for the detailed reply!

* Maxim Dounin <mdounin@mdounin.ru> wrote:

<snip>

> The 2147479552 is a limit applied by default to allow sendfile()
> to work with larger files on Linux up to 2.6.16 (see
> src/os/unix/ngx_linux_sendfile_chain.c for some comments). You can see the
> same limit on the first sendfile() call in the Ubuntu log as well.

Indeed, I had also seen a lot of reference to this "magic" number around,
so I thought it might be related to it.

> The strange thing here is that on Scientific Linux 6 the call
> pretends it send all the bytes in a single non-blocking call.
> This is not nginx expects to ever happen, and this is what causes
> the problem to appear. It would be interesting to dig further to
> understand what causes this SL6 behaviour.

OK, I did write a tiny test program to try and reproduce the problem on
the SL box: it tries to copy 4GB from an existing file in one sendfile
call:
https://gist.github.com/mathiasuk/cf46d0f0caf1dd597e59

As expected the sendfile calls return 2147479552, and the output file is
indeed 2147479552 bytes long, so this seems to work.
Here's the trace:
https://gist.github.com/mathiasuk/694177cf6446428f9498

I wonder if this could be because my test uses an output file and not a
socket. I'll try and investigate some more.

> Using sendfile_max_chunk with some large value is a correct
> workaround and expected to work fine.

Thanks!
Mathias

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