Re: alter rollback segment

"Paul Drake" <paled_at_home.com> wrote in message news:3AF3A020.5C4F4D0D_at_home.com...
> "Howard J. Rogers" wrote:
> >
> > That's the short form, anyway: creation of rollback segments is a bit
> > trickier than that, and sizing them appropriately is important. And I'd
> > also suggest you use locally managed tablespace to house them, rather
 than
> > the dictionary-managed version I've given you above. But whatever
> > refinements you care to add, the principles are as outlined above.
> >
> > Regards
> > HJR
> >
>
> Howard,
>
> being a bit on the less-than-bleeding-edge, I have not yet migrated my
> RBS tablespaces to LMTs.
> any gotchas?
> if you first have a dictionary managed RBS tablespace - did you convert
> it or drop it and re-create it as LMT?
>
> paranoid in NJ,
>
> Paul

Hi Paul,

No real gotchas that I can think of, except that you have to use the 'uniform size' version, not the autoallocate (anecdotally, anyway -I've never bothered wth autoallocate in the first place, so I've never tried).

Call me conservative, too, but I've never been a big fan of the conversion package, either -another thing I've never used. If it were my production database, I'd be creating a new LM tablespace from scratch, and dropping the old one -especially for RBS: it's no big deal to recreate the segments and do a bit of init.ora editing.

There is only one nasty with LM Rollback tablespace: you can't create the first rollback segment in it unless there is one non-system dictionary managed rollback segment (because creating that first one requires you to do DML on the bitmap at the header of the tablespace -and that's DML on a non-system tablespace, and hence if all you've got is the system rollback segment, you'll get that infamous ORA error to the effect that 'you can't use system rollback segment for updates in non-system tablespace'). So, you need to create one small rollback segment first in boring old dictionary tablespace (the SYSTEM tablespace will do fine -the fact that a rollback segment is housed in SYSTEM doesn't make it the system rollback segment). Once that is brought online, *then* you can create your first rollback segment in a locally managed tablespace. And once *that's* created and brought online, you can drop the temporary, dictionary-managed one, because now you *do* have a non-system rollback segment to handle all subsequent updates to the tablespace's bitmap.

Incidentally, if anyone tells you that you can create the SYSTEM rollback segment itself as locally managed, forget it. You can't, despite Oracle's own documentation saying otherwise (not that there's any real need to in the first place: the SYSTEM tablespace and all it contains is a law unto itself, best left to Oracle to cope with).

Regards
HJR Received on Sat May 05 2001 - 06:35:26 CDT