Issue Aborted connection 0 to db: 'unconnected' user: 'unauthenticated' host: 'connecting host' (Too many connections)

[Deleted member 209767]

Server operating system version

AlmaLinux

Plesk version and microupdate number

last

We have 2 servers crashing intermittently with all sites down until we restart MySQL

In the logs, there are hundreds of errors like this just before the downtime:

2023-05-05 5:57:15 0 [Warning] Aborted connection 0 to db: 'unconnected' user: 'unauthenticated' host: 'connecting host' (Too many connections)

What could be causing this? How can I debug this issue?

 

[scsa20]

What is your database version? Cause searching the web there appears to have been a known issue that was patched in a later release.

 

[Deleted member 209767]

One server is running MariaDB 10.3 and the other one 10.5
I will try upgrading it and see if it helps

 

[Peter Debik]

"Too many connections" could also simply be caused by too many concurrent connections. This happens when either too many users connect at the same time or if scripts create persistent database connections (they open one but never close it again). You can set two important parameters in the [mysqld] section of /etc/my.cnf:

max_connections=<some high integer number, e.g. 2000>
max_user_connections=<some low integer number, e.g. 100>

Then restart the database server for these settings to take effect. Most often the max_user_connections set to a low number will keep your server available, because it will keep single users from occupying all possible connections to the database server. If the user reaches his personal limit, he won't be able to add another connection, but other users will. You can check the connections simply by looking at the database processlist (>show processlist), there you will see which user is doing what.