Alain Raap

As nobody could answer my question about running Redis via a Unix socket I have stopped to try to get this working in Moodle.
Testing with the benchmark of Redis showed much better performance when using Redis on the same application server of Moodle. Maybe interesting to have a look at this point for a future release of Moodle?

Your hits percentage is very low, should be at least 97%, 98%. Did you check the Redis log for errors like 'THP enabled', 'vm.commit_memory' and other possible problems? This could make a difference in your perfomance.

Other question, you are using Redhat 7, is Selinux enabled in your environment? If so, I'd check the 'denied' errors in your audit.log (cat /var/log/audit/audit.log | grep denied). If you see a lot of errors, you'll probably have to fix this in a Selinux policy file.

Did you try the redis-benchmark on your site? It gives a summary of your Redis performance: https://www.tutorialspoint.com/redis/redis_benchmarks

In our Moodle environment we don't have more than one application server. We store the cache, localcache and temp files on the application server and that is much faster, also for the temporary backup files that aren't saved over the network anymore. It works fine for us.