I can think of no practical(?) use except for parallel server.
In parallel server an instance will aquire private rollback
segments specified in init.ora. If none (or too few) are
specified, it will aquire public rollback segments. Public
rollback segments are, in my opinion, only useful in an OPS
environment in an active/passive configuration. (I prefer
private, even then.)
I have seen an OLTP OPS system with activity on both nodes and public
rollback segments all around - and crippling pinging on rollback.
The huge disadvantage is the OPS overhead if two instances obtain
two rollback segments where some set of blocks in one is covered
by the same PCM lock as some set of blocks in the other. Since
rollback segments are so write intensive, overhead can be
tremendous.
It is easy to avoid this altogether. Simply create two distinct
tablespaces (for the sake of discussion, call them RBS1 & RBS2)
with two distinct datafiles for rollback. Create private rollback
segments for one instance in RBS1 and the other in RBS2. Assign
very few fixed locks to these datafiles.
Real Application Clusters are going to be a new ball game
with system managed rollback and default releasable locks.
Fixed fixed locks are not really eliminated, but it seems
that using them will disable cache fusion entirely.
It will be interesting.
-Don Granaman <OraSaurus>
Jenner Mike wrote:
>
> Isn't the concept of a private RBS only applicable to parallel server
> setups?
> - Mike.
>
> -----Original Message-----
> Sent: 09 May 2001 16:21
> To: Multiple recipients of list ORACLE-L
>
> Hi all,
> This brings me to a stupid question then. What is the true
> difference
> between a public and a private rollback segment? Because if I just think
> about it like a normal human being I would think that if a user made a
> Private rollback segment then only that user could use it, but of course I
> know that can't be the case.
> Kev
>
> -----Original Message-----
> Sent: Wednesday, May 09, 2001 10:26 AM
> To: Multiple recipients of list ORACLE-L
>
> Nixon,
>
> While SET TRANSACTION can be used to assign a rollback
> segment to a transaction, it cannot be assigned exclusively to
> that transaction as you have found.
>
> The ability to assign a rollback segment to a transaction and
> make it read-only for all others is something I've wanted myself
> for many years, and I know it's been on the official 'wish list' of
> requested changes by IOUG for some time.
>
> Maybe 9i? Anyone know?
>
> Jared
>
> On Wednesday 09 May 2001 01:40, [EMAIL PROTECTED] wrote:
> > Hi All,
> >
> > Here is my environment;
> >
> > NT v4
> > Db Oracle Workgroup v8.1.6
> >
> > Rollback Segments
> > SEGMENT_NAME OWNER TABLESPACE_NAME
> > ------------------------------ ------ ------------------------------
> > SYSTEM SYS SYSTEM
> > RBS0 PUBLIC RBS
> > RBS_P1 SYS RBS
> > RBS_P2 SYS RBS
> > RBS_P3 SYS RBS
> > RBS_P4 SYS RBS
> > RBS_P5 SYS RBS
> >
> >
> > Is it possible to assign one public rollback segment explicitly to one
> > particular transaction? I tried using SET TRANSACTION USE ROLLBACK SEGMENT
> > but other users I found out can still use it. So, I guess the best
> > alternative is to set that RB segment to OFFLINE after using and set
> ONLINE
> > before executing the SET TRANSACTION ... Do you know how it can be done
> > inside Forms?
> >
> > Thanks in advance!
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.com
> --
> Author: Jared Still
> INET: [EMAIL PROTECTED]
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> Author: Jenner Mike
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