Hi Philippe !

It is a good idea. Specially if you have many qsos in log (>10000) backing up starts to take time.
How ever it is not so simple just count qso amount and see if backup is needed.

What If you have not had qsos, but done some editing to log or up/dn-loading qsl informations?
That must also be counted as change that needs backup.

But as said Idea is good.
Meanwhile easiest way is to unset auto backup and do it manually only if here is need for it.

Or more complicated (but flexible) way:
Make your log to your local mysql server, do not use protected database mode that starts only with cqrlog (as it is as default).

You have installed mysql (or Mariadb). So it is running there all the time as daemon.
Make a mysql user (cqrlog, pass cqrlog) using mysqladmin or webmin or any other way you like.
Google gives help. Use words: mysql create user

After that give that user so much power that it can create and admin databases.

When cqrlog starts (or from "Open or create new log") put server name "localhost" and port "3306" (that is standard mysql server port) user cqrlog pass cqrlog (same as you just created.
Then make new log. Transfer all your qsos to that with ADIF export/import from other log. Use Utils/Configuration/Export-Import to copy also log properties from old to new one.
NOTE: You have to change server pot number while swithing the old and new log.

You have now your new log running in your local mysql server and it is accessible also when cqrlog is NOT running.
Then you may do what ever you like. Replicate it to another mysql server, make search with mysql console, and most important:

Make backup with mysqldump.

This is better than adif backup as it saves also all your settings and window positions etc. Simply everything that goes with your log.

Using Google for help gives thousands of examples how this all can be done.
It is worth of learning.

--
Saku
OH1KH