> Is this possible?

http://www.firebirdsql.org/file/documentation/reference_manuals/user_manuals/html/gfix-cmdline.html

Sure.

see parameter: -housekeeping set sweep interval <n>

usage: gfix [options] <database>
plausible options are:
-activate activate shadow file for database usage
-attach shutdown new database attachments
-buffers set page buffers <n>
-commit commit transaction <tr / all>
-cache shutdown cache manager
-full validate record fragments (-v)
-force force database shutdown
-fetch_password fetch_password from file
-housekeeping set sweep interval <n>
-ignore ignore checksum errors
-kill kill all unavailable shadow files
-list show limbo transactions
-mend prepare corrupt database for backup
-mode read_only or read_write
-no_update read-only validation (-v)
-online database online <single / multi / normal>
-prompt prompt for commit/rollback (-l)
-password default password
-rollback rollback transaction <tr / all>
-sql_dialect set database dialect n
-sweep force garbage collection
-shut shutdown <full / single / multi>
-two_phase perform automated two-phase recovery
-tran shutdown transaction startup
-use use full or reserve space for versions
-user default user name
-validate validate database structure
-write write synchronously or asynchronously
-z print software version number

http://www.firebirdsql.org/file/documentation/reference_manuals/user_manuals/html/gfix-housekeeping.html

Disabling Automatic Sweeping

If you set the sweep interval to zero then automatic sweeping will be
disabled. This implies that there will be no automatic housekeeping done
so your database performance will not suffer as a result of the
processing requirements of the automatic sweep.


bye...
eMeL