Buffering issues with nginx

Valentin V. Bartenev vbart at nginx.com
Fri Jul 21 21:05:08 UTC 2017

On Friday 21 July 2017 13:45:51 Dan34 wrote:
> In short, these could affect my case: SO_RCVBUF, SO_SNDBUF on nginx side and
> whatever buffering nginx uses for handling data. I run that same test with
> 25MB data and I got totally identical result: 12.5MB was buffered on nginx
> side. That stuff that could affect my case cannot really add up to 12.5MB
> and 10 minute of time.
> There is a wild possibility that tcp window scaling resulted in some huge
> window on node->nginx side and ended up storing that 12MB in tcp window
> itself but i'm not sure if TCP window should be accounted into these
> SO_RCVBUF or that RCVBUF is extra data on top of internals of TCP.

nginx doesn't set SO_RCVBUF/SO_SNDBUF by default, which usually means that 
kernel will use system defaults and auto-scalling. 

> So,.. any ideas how come nginx ends up buffering 12.5MB data?

You should check tcpdump (or wireshark) to see where actually 12.5MB
of data have been stuck.

  wbr, Valentin V. Bartenev

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