Re: ROLLBACK SEGMENT?

From: <Rajesh.Rao_at_chase.com>
Date: Fri, 25 Jan 2002 08:44:46 -0800
Message-ID: <F001.003FB432.20020125083523@fatcity.com>

John,

I DISAGREE. The gymnastics of assigning a large rollback segment to an export could avoid the snapshot too old error.

I agree with Jeremy when he says export does not generate rollback. But I was trying to impress upon him that still an export could end up with the snapshot too old message, particularly if there are plenty of active DML transactions happening while the export is in progress, or if the export uses the consistent parameter, or the rollback segments are not properly sized.

To stress my point further, Note:22836.1 on Metalink. I rest my case ;-)

Raj

orantdba <orantdba_at_netscape.net>@fatcity.com on 01/25/2002 08:20:25 AM

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Hi Raj,

Interesting that you first agree with Jeremy and then argue with him. It is precisely because
export does not generate rollback that the "gymnastics" of taking all of the other rbs's offline
will not help anything. It might make you feel better, however :-).

John

Rajesh.Rao_at_chase.com wrote:

Export doesn't generate any rollback, right, so what is it supposed to accomplish by doing this incantation?

Sorry to press the point, but could you elaborate on how that "COULD" possibly make any difference for 'snapshot too old'?

For the same reason, any other transaction could end up with a snapshot too old error. Export does not generate any rollback, but there could be users performing DML operations on the table that is being exported, and the export needs to be redirected to read from the rollback segments. The likelihood of the error being thrown up especially if one uses the consistent parameter could be very high, if you dont have a large enough rollback segment without an optimal clause.

Raj

Jeremiah Wilton <jwilton_at_speakeasy.net>@fatcity.com on 01/23/2002 11:20:40 AM

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ts of list ORACLE-L <ORACLE-L_at_fatcity.com> cc:

On Tue, 22 Jan 2002, Rajesh.Rao_at_chase.com wrote:

Hmmmm ... "COULD" help in avoiding snapshot too old errors.

Sorry to press the point, but could you elaborate on how that "COULD" possibly make any difference for 'snapshot too old'?

--

Jeremiah Wilton
http://www.speakeasy.net/~jwilton

Jeremiah Wilton <jwilton_at_speakeasy.net> wrote:

So what does it accomplish to "assign export [to] a particular rollback segment?"

Export doesn't generate any rollback, right, so what is it supposed to accomplish by doing this incantation?

On Tue, 22 Jan 2002, Jason Rowski wrote:

... you can use the following trick to assign export a particular rollback segment -

Create a rollback segment tablespace with one large segment and bring it online before export.
Offline all existing rollback segments.
Export the database
Offline the large tablespace created earlier.
Bring back the orginals rollback segments online.
- Seema Singh <oracledbam_at_hotmail.com> wrote:

Can I use one rollback segment at time of export?Is yes,then
SET TRANSACTION USE ROLLBACK SEGMENT
rollbacksegmentname;

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