503 Max restarts limit reached

So we had "503 Max restarts limit reached" problem on our production while doing some batch operations and some edits of entities. Problem for both was that server response was slow as both have large queries running which take more than 20 seconds(yeah should be optimized and probably add some indexes to fields).

Getting country name from country code

To get full country name you need to use CountryManager class and you can then get all the info you need.  So lets say you have some country code store in $shipping_code variable, to get full country name

Checking all crontabs on server

To get all crontabs from users on your system write this one liner

for user in $(getent passwd | cut -f1 -d: ); do echo $user; crontab -u $user -l; done

to check other crons you need to see what is in for example 

ls -la /etc/cron.daily

or

JSON:API disable caching locally

To disable caching while testing your JSON:API endpoints you should put this into your settings.php

$settings['cache']['bins']['dynamic_page_cache'] = 'cache.backend.null';

but for this to work, you need to define this service null, which should be added as