Hi.

I have limited knowledge in this matter then maybe someone correct me.

Firebird work with record formats. When you add new field, firebird create only new record format for the table and do nothing with data stored. When you update some record and it is in old format it is then reformatted.

I suppose this depend on the kind of change. If i remember, there is a limit of 255 record formats for particular table. If you reach the limit, you must make backup/restore.

Regards,