Magento – Magento 2 – Very slow performance, Cache/static files issues after disabling cache and flushing static files cache

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!

In developer mode, M2 does not generate static files. It should create symlinks to them from the various modules. If you however have ran setup:static-content:deploy and have those files in place, it won't update them. Try removing all static files and see if Magento links to them (be careful not to remove the actual files if you have symlinks)