RE: Rollback Segments

Kev,

PUBLIC and PRIVATE Rollback segments are not specified for ALL or SPECIFIC USER use. You can specify a certain transaction to use a specific rollback segment, as stated in the post below. PUBLIC and PRIVATE Rollback Segments have to do with the instances that utilize them. For example, in a distributed environment or on a Parallel Server environment, PUBLIC RBSs can be used by either INSTANCE, as opposed to the RBSs created by just one instance in the cluster.

Don't worry, Dulcian doesn't use databases that large ;-)

Ed Haskins
Oracle DBA
Verizon Wireless (and former Dulcian employee)

ALSO...I just read Anita's Post, and she is also correct...I just added the other angle. Here is some verbiage from the docs:

Public and Private Rollback Segments
Public and private rollback segments do not have performance differences. However, private rollback segments provide more control over the matching of instances with rollback segments. This allows you to locate the rollback segments for different instances on different disks to improve performance. Therefore, use private rollback segments to reduce disk contention in high-performance systems.

Public rollback segments form a pool of rollback segments that can be acquired by any instance needing an additional rollback segment. Using public rollback segments can be disadvantageous, however, when instances are shut down and started up at the same time. For example, instance X shuts down and releases public rollback segments. Instance Y starts up and acquires the released rollback segments. Finally, instance X starts up and cannot acquire its original rollback segments. Acquiring a public rollback segment can also be made at startup if TRANSACTIONS and TRANSACTIONS_PER_ROLLBACK_SEGMENTS are not properly set.

You can use public rollback segments to improve space utilization. If you create only one large public rollback segment for long-running transactions that run on different instances each month, the rollback segment can be taken offline and brought back online or "moved" from one instance to another to better serve instances with the heavier workloads.

By default a rollback segment is private and is used by the instance specifying it in the parameter file. Specify private rollback segments using the parameter ROLLBACK_SEGMENTS.

Once a public rollback segment is acquired by an instance, it is then used exclusively by that instance.

Once created, both public and private rollback segments can be brought online using the ALTER ROLLBACK SEGMENT command.

-----Original Message-----
Sent: Wednesday, May 09, 2001 11:21 AM
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, Nixon_Villanueva_at_manulife.com 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!

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