Magento 2.2 Performance – Extremely Slow with 100% Processor Usage After Setup:Upgrade

I think that it's the Magento part :)

Sincerely, though, Magento is not meant to be hosted on a shared-resource server and there is no magic bullet that will fix these 'issues'. However, I have had tremendous luck hosting very small shops at Amazon Web Services' EC2. At the time of this writing, their Spot instances run at about $115/year. That's a virtualized, dedicated environment.

Perhaps you're not devops and you don't want to manage the infrastructure/environment at all. I would check this list out of hosting partners with Magento and contact one of them:

http://www.magentocommerce.com/partners/hosting

I investigated even more and I think I finally solved the issue. So what can you do to analyse such an issue?

1. In order to have a good idea when the cache becomes too large and if the problem is really the cache size, add a cronjob which calls the following script e.g. each 15 minutes:

   #!/bin/bash
   
   # this script is an attempt to check if the full cache is the real performance problem
   # it should be called regularly as a cronjob
   
   cache_dir="/html/shop/var/cache/"
   log_file="/html/cache_log"
   
   line=$(date)
   line="$line Size of cache directory: $(du -hs $cache_dir)"
   echo "$line" >> $log_file
   
   line=$(date)
   line="$line Total cache tags: $(find $cache_dir'cm-tags/' -type f | wc -l)"
   echo "$line" >> $log_file
   

   Then you can analyse the contents of /html/cache_log to see how the cache size develops, when your page becomes too slow and if the root cause is really the cache.

2. Analyse your cache files. Therefore, it is quite helpful to write all cache files into a log file with e.g.:

   ls -R /html/shop/var/cache > /html/cachefiles
   

   Have a look at this file and the file names within. What kind of cache files are there? Is there anything suspicious? In my case, there were a whole lot of cache files containing AMSHOPBY in their file name - a reference to the Amasty Improved Navigation (Amasty_Shopby) extension. It was creating a whole lot of cache files. Some of them looked quite weird to me. Disabling the Amasty Improved Navigation cache solved the problem instantly. I contacted their support with a detailed description and the support was really good. The caching strategy was quickly completely overhauled and is now much better. They promised to integrate the patch in the next version of the extension, so every version > 2.8.3 should be fine.

Good luck in finding the root cause for your big cache!