RE: [Q] Public and private rollback segment?

Additionally: 'create rollback segment ...' defaults to 'private' and the only time when I needlessly use a keyboard is to send a message like this one

-----Original Message-----
Sent: Thursday, October 17, 2002 1:59 PM To: Multiple recipients of list ORACLE-L

This is my understanding of "private" versus "public" rollback segments:

• Private RBS can be brought online only via explicit ALTER ROLLBACK SEGMENT xxx ONLINE command.
• The "init.ora" parameter ROLLBACK_SEGMENTS is only a list for the automatic execution of ALTER ... ONLINE command at database instance startup, so it is essentially the same as an explicit ALTER ... ONLINE command...
• Public RBS can also be brought online via explicit ALTER ... ONLINE or "init.ora" parameter ROLLBACK_SEGMENTS, if you wish...
• Public RBS can also be brought online at instance startup according to the formula using the parameters (TRANSACTIONS / TRANSACTIONS_PER_ROLLBACK_SEGMENT). In an OPS/RAC environment, this allows each instance to select as many public RBS from a "pool" of public RBS. The mechanism still works even in non-OPS/RAC environments too...
• The use of public RBS is not restricted to OPS/RAC, but it doesn't make much sense without it...
• it doesn't make much sense *with* OPS/RAC either, but that's just my opinion...

The upshot is that the only difference between public and private RBS is this additional ability to forego the onlining at instance startup via the ROLLBACK_SEGMENTS parameter or subsequently via ALTER ... ONLINE statements. Instead, at instance startup the simple formula using TRANSACTIONS and TRANSACTIONS_PER_ROLLBACK_SEGMENT is used. Since these are all static parameters and the difference in functionality occurs at only one point-in-time (i.e. instance startup), it really is purely a matter of style. I see no advantage to using public RBS at all...  

Corrections? Comments? Questions?  

• Original Message ----- bbaker_at_denvernewspaperagency.com> To: "Multiple recipients of list ORACLE-L" < <mailto:ORACLE-L_at_fatcity.com> ORACLE-L_at_fatcity.com> Sent: Thursday, October 17, 2002 10:09 AM

>
>
> Can't remember where I copied this from, but I believe it came from
> metalink. I don't have a version associated with it, so things might have
> changed in v9.
>
> HTH
> Barb
>
>
> Public vs. Private Rollback Segments
> ------------------------------------
> A common misconception about `Private' rollback segments is that they are
> segments reserved for a particular use or a particular transaction. The only
> difference between Public and Private rollback segments is in relation to
> the Parallel Server Option. A public rollback segment can be acquired
> implicitly by any instance in a parallel server environment. A private
> rollback segment must be explicitly acquired by a particular instance using
> the rollback_segments parameter. If not using OPS, the difference between
> the two is insignificant.
>
>
> > ----------
> > From: dist cash[SMTP:mccdba_at_hotmail.com]
> > Reply To: <mailto:ORACLE-L_at_fatcity.com> ORACLE-L_at_fatcity.com
> > Sent: Thursday, October 17, 2002 9:18 AM
> > To: Multiple recipients of list ORACLE-L
> > Subject: [Q] Public and private rollback segment?
> >
> >
> >
> >
> > We have ORACLE 8.1.7.4 running on NT. My questions are:
> >
> > 1. What difference between public rollback segment and private segement?
> >
> > 2. what is benefit on public segment than private segment?
> >
> > 3. does public segment only use on "paraller server (RAC)"?
> >
> > Thanks.
> >
> >
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Author: Inka Bezdziecka
  INET: IBezdziecka_at_cupe.ca

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