A typical request is to pull only THOSE records from Firebird servers, WHICH CHANGED since last query.
With current engine model this is a very complex thing to do.
It would make programmers life much easier if there would be an "auto-sequencer field", like: RDB$LAST_MODIFIED attached to every table by default.
That would be auto-updated on every insert and update by a global system generator AFTER_COMMIT. (NOT during transaction, like triggers do!)
SELECT o.* FROM orders o WHERE o.RDB$LAST_MODIFIED > 5489852;
Or could be the new replication system's values used for this?