WARNING: [pool staging_4pens_com] server reached max_children setting (5), consider raising it

Reaching this limit would be caused by long-running PHP processes, causing additional PHP processes from additional site traffic to begin to stack and queue which can lead to increased site load time, and eventually result in timeouts.

Solution:

increase memory_limit in php.ini to 128M

using root access increase max children setting to 15

sudo grep max_children /var/log/php?.?-fpm-sp.log.1 /var/log/php?.?-fpm-sp.log

If any of your apps have reached their max_children limit, you’ll see output like this:

[24-Apr-2017 19:56:17] WARNING: [pool my-wordpress-app] server reached max_children setting (20), consider raising it

To increase the max_children setting for an app, SSH in to your server as root and rename this file:

/etc/phpX.Y-sp/fpm-pools.d/APPNAME.d/main.conf

to this:

/etc/phpX.Y-sp/fpm-pools.d/APPNAME.d/main.custom.conf

Next, edit the file and change the value on this line to the maximum number of PHP processes you want the app to be able to have running:

pm.max_children = 20

Last step , restart that PHP server version with the command:

sudo service phpX.Y-fpm-sp restart