In my case, the problem appears to be the MySQL database. Since I set the values in my.cnf as follows, everything appears to be working fine:
innodb_buffer_pool_size=1024M
query_cache_size=64M
You can find details to this here: Troubleshooting slow performance of the MySQL on Plesk server
I made the following screenshots when the server was working and when it was not (the two right underneath each other, about five minutes apart). Do you have any suggestions what might be wrong?
@IgorG: Can I use the Plesk support for a version of Plesk that I did not licence myself? It was...
Hello,
a virtual server throws error 502 or 504 bad gateway several times a day. When this happens, log in to Plesk is usually possible, but very slow.
In the proxy_error_log of the domain that has the most visitors (and thus is most affected by the problem) I frequently see the following...