At 12:38 PM 18/03/2003 +0100, you wrote:

> > Just to add to Helen's comments. A metadata change is any kind of DDL,
>e.g.
> > if you set an index to inactive before doing some batch inserts and then
> > set it active afterwards, you've already done two metadata changes. But
> > these 254 changes are to each database object within the database, so
>we're
> > not talking about 254 changes in total to the database.
>
>Just curiosity,
>
>why does this limit exist? Does it exist in all the RDBMS?

Metadata are stored in the database, in system tables. These are just
regular database tables, so multi-versioning applies to these rows just as
to any database row. The limit ensures that "reasonable" housekeeping will
be performed on the system tables and their indices will be kept in good shape.

As to other DBMSs, those that imitate Firebird's versioning engine AND
store the system tables inside the database would have to deal with cleanup
of system tables.

heLen