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Re: $request_time variable = 0 for small files.

Clima Gabriel
March 07, 2024 05:36AM
0.000 sysctl -w net.ipv4.tcp_rmem="4096 4096 4096"
0.072 sysctl -w net.ipv4.tcp_rmem="512 512 512"
0.106 sysctl -w net.ipv4.tcp_rmem="256 256 256"

You're right.
This was invaluable, thank you!

On Thu, Mar 7, 2024 at 11:46 AM J Carter <jordanc.carter@outlook.com> wrote:

> Hello,
>
> On Thu, 7 Mar 2024 08:17:23 +0200
> Clima Gabriel <clima.gabrielphoto@gmail.com> wrote:
>
> > Greetings,
> > I'm investigating a bug, super easy to reproduce.
> > Thought you might be curious.
> >
> > Minimal Nginx config. Create two files. 100M and 1M:
> > dd if=/dev/zero of=/var/www/file100M bs=100M count=1
> > dd if=/dev/zero of=/var/www/file1M bs=1M count=1
> >
> > Get them files:
> > curl --limit-rate 10M -o /dev/null 127.0.0.42:80/file100M
> > curl --limit-rate 100k -o /dev/null 127.0.0.42:80/file1M
> >
> > Both transfers take ~10s, but Nginx logs 0s request_time for the small
> file.
> >
>
> This isn't an issue with nginx. The response nginx sends
> truly does take 0s to reach the client's socket.
>
> Curl's limit-rate flag only applies at the application layer, but it has
> no effect on curl's tcp socket, or it's buffers/how fast things are
> read into the buffer. The entire response sent by nginx is being
> received into into curl's tcp socket buffer instantly, which is
> auto-scaled to a large window size because you are making these
> requests from local machine.
>
> You can temporarily set tcp read window to smallest possible minimum,
> default, and maximum to confirm. Like this:
>
> sysctl -w net.ipv4.tcp_rmem="4096 4096 4096"
>
> or just view tcp traffic via wireshark.
>
> > master_process off;
> > daemon off;
> > error_log /dev/stderr;
> > events {}
> > http
> > {
> > log_format req_time "$request_time";
> > server
> > {
> > server_name 127.0.0.42;
> > listen 127.0.0.42:80;
> > root /var/www/;
> > index index.html;
> > location /
> > {
> > access_log /dev/stderr req_time;
> > error_log /dev/stderr;
> > }
> > }
> > }
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Subject Author Posted

$request_time variable = 0 for small files.

Clima Gabriel March 07, 2024 01:18AM

Re: $request_time variable = 0 for small files.

J Carter March 07, 2024 04:46AM

Re: $request_time variable = 0 for small files.

Clima Gabriel March 07, 2024 05:36AM



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