On Thu, 07 Mar 2019 13:33:39 -0500
"wkbrad" <nginx-forum@forum.nginx.org> wrote:

> Hi all,
>
> I just wanted to share the details of what I've found about this
> issue. Also thanks to Maxim Dounin and Reinis Rozitis who gave some
> really great answers!
>
> The more I look into this the more I'm convinced this is an issue
> with Nginx itself. I've tested this with 3 different builds now and
> all have the exact same issue.
>
> The first 2 types of servers I tested were both running Nginx 1.15.8
> on Centos 7 ( with 1 of them being on 6 ). I tested about 10 of our
> over 100 servers. This time I tested in a default install of Debian
> 9 with Nginix version 1.10.3 and the issue exists there too. I just
> wanted to test on something completely different.
>
> For the test, I created 50k very simple vhosts which used about 1G of
> RAM. Here is the ps_mem output.
> 94.3 MiB + 1.0 GiB = 1.1 GiB nginx (3)
>
> After a normal reload it then uses 2x the ram:
> 186.3 MiB + 1.9 GiB = 2.1 GiB nginx (3)
>
> And if I reload it again it briefly jumps up to about 4G during the
> reload and then goes back down to 2G.
>
> If I instead use the "upgrade" option. In the case of Debian,
> service nginx upgrade, then it reloads gracefully and goes back to
> using 1G again. 100.8 MiB + 1.0 GiB = 1.1 GiB nginx (3)
>
> The difference between the "reload" and "upgrade" process is
> basically only that reload sends a HUP signal to Nginx and upgrade
> sends a USR2 and then QUIT signal. What happens with all of those
> signals is entirely up to Nginx. It could even ignore them if chose
> too.
>
> Additionally, I ran the same test with Apache. Not because I want to
> compare Nginx to Apache, they are different for a reason. I just
> wanted to test if this was a system issue. So I did the same thing
> on Debian 9, installed Apache and created 50k simple vhosts. It used
> about 800M of ram and reloading did not cause that to increase at all.
>
> All of that leads me to these questions.
>
> Why would anyone want to use the normal reload process to reload the
> Nginx configuration?
> Shouldn't we always be using the upgrade process instead?
> Are there any downsides to doing that?
> Has anyone else noticed these issues and have you found another fix?
>
> Look forward to hearing back and thanks in advance!
>
> Posted at Nginx Forum:
> https://forum.nginx.org/read.php?2,283216,283309#msg-283309
>
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Well for what it's worth, here is my result.
centos 7 3.10.0-957.5.1.el7.x86_64 #1 SMP Fri Feb 1 14:54:57 UTC 2019
x86_64 x86_64 x86_64 GNU/Linux

sh-4.2# nginx -v
nginx version: nginx/1.14.0


sh-4.2# ps_mem | grep nginx
4.7 MiB + 2.1 MiB = 6.7 MiB nginx (2)
sh-4.2# systemctl reload nginx
sh-4.2# ps_mem | grep nginx
1.7 MiB + 4.0 MiB = 5.7 MiB nginx (2)
sh-4.2# systemctl restart nginx
sh-4.2# ps_mem | grep nginx
804.0 KiB + 3.5 MiB = 4.2 MiB nginx (2)
sh-4.2# ps_mem | grep nginx
2.9 MiB + 2.9 MiB = 5.8 MiB nginx (2)
sh-4.2# ps_mem | grep nginx
2.9 MiB + 2.9 MiB = 5.8 MiB nginx (2)
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