Sometimes you want to reduce disk usage on certain servers by adjusting the time that binary logs are kept. Also, some installations of MySQL and MariaDB have suffered from a very-hard-to-catch bug where the binary logs end up not getting automatically expired (basically, the expire_logs_days option doesn’t always work effectively).
A workaround can be scripted, but typically the script would specify the exact datetime to which the logs need to be kept. The reference manual and examples all do this too, quite explicitly, noting:
The datetime expression is in the format ‘YYYY-MM-DD hh:mm:ss’.
However, the actual command syntax is phrased as follows:
PURGE { BINARY | MASTER } LOGS { TO ‘log_name’ | BEFORE datetime_expr }
and that indicates much more flexibility in the parser: “datetime_expr” means that you can put in an arbitrary temporal expression!
So let’s test that, with a functional equivalent of expire_logs_days=14:
FLUSH BINARY LOGS;
PURGE BINARY LOGS BEFORE (NOW() – INTERVAL 14 DAY);
And yep, that works (and the extra parenthesis around the expression are not required, I just did that to show clearly what the expression is).
Now, I’m not the first person to use this construct, there are several posts online from recent years that use an expression with PURGE BINARY LOGS. I’m not sure whether allowing datetime_expr is a modification that was made in the parser at some point, or whether it was always possible. Fact is, the reference manual text (MariaDB as well as MySQL) only provide examples with an absolute ISO datetime: ‘YYYY-MM-DD HH:MM:SS’.