> can you, please, tell me, if adding column to system tables is allowed? In
> table RDB$RELATION_FIELDS is for example column RDB$DESCRIPTION. Can I add
> column DESCRIPTION2 BLOB?
> How can this impact the FB functionality or performance?

You could - but I don't see the point. Why do you need the extra field? Is
it for user information - if it is you should put it in a specific user
table, if you want to extend the system metadata for a particular reason
then it becomes an overall decision for the firebird developers.

The system metadata is created by the engine, every time a new database is
created and on a restore when it is reloaded. So even if you do add the
column, you are liable to lose it at some time in the future......

Regards
Paul