mariadb (MySQL) stopped flushing relay-bin log after mysqld-relay-bin.999999

We have a pretty big MariaDB master-slave setup, which is really under heavy load and suddenly one of our slaves stopped purging relay logs! And soon the free space got less and it was clear were were going to run out of space for the data partition.

Here is the problem we have only 49G left free space for our mysql datadir “/var/lib/mysql-datadir”. You can see the replication is OK and running (it’s not behind – “Seconds_Behind_Master: 0”), the

Relay_Log_File says mysqld-relay-bin.999999

but it is not true! You can see there are tones of more relay logs after “mysqld-relay-bin.999999” – in fact the current MySQL relay binlog file is “mysqld-relay-bin.1071413” (look below we included a listing of the datadir).

And “FLUSH RELAY LOGS” does not help, at all!

It just not freed any byte on the partition and no files were removed after “mysqld-relay-bin.999999” as before.
Keep on reading!