RE: ** can two processes use the same rollback extent

From: Freeman Robert - IL <FREEMANR_at_tusc.com>
Date: Sat, 27 Dec 2003 22:54:25 -0800
Message-ID: <F001.005DB228.20031227225425@fatcity.com>

1) rollback segment will not shrink.

Correct, assuming you do not shrink it manually.

2) It will keep growing till tablespace fills up.

Correct assuming that you have a SQL statement that causes the rollback segment to grow in such a way and that you have no constraints on the rollback segments to prevent unconstrained growth (e.g. maxextents). Note that this may not be a good thing... if you have one transaction that causes one rbs to grow really large, that may prevent growth of other rbs's. Unless you are manually assigning rollback segments to every transaction, that could have negative consequences.

It is, IMHO, best to have use automated undo, if possible, then you don't need to worry about these things. If you can't use automated undo, then create a nice big tablespace, but also use optimal, setting it to a reasonable size.

3) And there will be no 'snapshot too old' errors?

Wrong. Even with large rollback segments, 1555's are possible depending on a number of things.

Robert G. Freeman
Technical Management Consultant
TUSC - The Oracle Experts www.tusc.com
630.819.9077 Cell (It's everywhere that I am!)
Author of several books you can find on Amazon.com!

-----Original Message-----
From: A Joshi [mailto:ajoshi977@yahoo.com]
Sent: Sunday, December 28, 2003 12:39 AM
To: Multiple recipients of list ORACLE-L
Subject: Re: ** can two processes use the same rollback extent

Hi,

A simple rollback segment question. If I do not set a optimal then can I assume following

1) rollback segment will not shrink.

2) It will keep growing till tablespace fills up.

3) And there will be no 'snapshot too old' errors?

Thanks

A Joshi <ajoshi977@yahoo.com> wrote:

Hi,

One rollback segment can be used by multiple transactions/processes but what about the extents? Is it safe to assume that only one transaction/process can use one extent? What is a good way to size the extent for warehousing tasks? Or guess the rollback generated and size needed.

Thank You

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Author: Freeman Robert - IL
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Received on Sun Dec 28 2003 - 00:54:25 CST