Hi Stefano, To decrease database size you need to make backup/restore.
Then, to keep its growth under control, you need to perform the following maintenance procedure: 1) stop Firebird server and then start it immediately (less than 3 sec downtime). 2) run gfix -sweep -user SYSDBA -pass masterkey <database_path> that's all. Regards, Alexey Kovyazin IBSurgeon