Purge database - what it exactly does

Hi,
I read through the documentation but I am not sure what is the real effect - do I understand that I will lose older detailed statistics for sensors but hourly / daily statistics will remain (i.e. charts will work even for the past period)?
Thanks a lot.
Regards,
Lubos

Yes.

State and event history older than your purge keep days setting are deleted but long term statistics are retained.