Magento – Magento 2 strong performance issues (cron)

As the question seems to be not very magento centric, here is my not very magento centric answer.

OpCode caching and DB optimizations are a good way to accelerate your web applications to some extent. But the benefit will be relatively moderate. To get a real speed boost you should consider using varnish cache. It is open source, easy to configure and easy to integrate with magento thanks to freely available modules for magento.

There is also a good article with a brief overview of how it works: http://www.fabrizio-branca.de/make-your-magento-store-fly-using-varnish.html

Especially consider the chart:

The only way I am able to solve it is by rebooting the entire server

Fire your hosting provider, immediately. The only time a server should be powered off is to physically upgrade it, or install a new kernel - never to solve a problem. If they can't provide a solution to such a simple issue, they aren't a company worth using.

Your issue is fairly clear, you are lacking instrumentation.

You should be graphing every single application and event on your server in initimate detail, so that you can correlate the sequence of events leading up to a slow query incident to identify a cause.

If everything performs normally, then suddenly slows down, I'd be inclined to review,

• Varnish hit rate - does it plummet at the time of the slowdown?
• Inbound traffic rate - do you see an increase in traffic, do you see an increase from a single IP?
• Cache store utilisation - has someone flushed a cache, or have several entries expired simultaneously?
• Hardware activity - what else is happening on the server at the time, is I/O high, SYS CPU etc. Is it cloud/VPS - if so, what is the hypervisor doing?

There could be dozens of possible causes, all of which should take seconds to identify and fix, but without instrumentation - you can't simply guess your way through a fix. You'll just cause further problems blindly making adjustments.