Re: rollback segment usage

Answers intermixed with original post

In article <7978ia$9vc$1_at_nnrp1.dejanews.com>,   nguffey_at_jdriscoll.com wrote:
> Several Questions: 1. When Oracle writes a before image to a rollback
> segment, is it writing only the row being modified, or is it writing the
> entire datablock?

The first time a user session modifies a block the entire block has to be copied to the rbs segment. The next time a block is copied only vector information has to be copied to the rbs segment.

> 2. Does a SCN apply only to the row on a data block being
> modified, or to the entire block?

I read, but I do not remember in what book, that the answer depends on it you are accessing the table via full table scan or index read. When the block is accessed via a full table scan the scn applies to the block, but if the access is via an index, the scn is at the row level.

>3. Multiple transactions can use the same
> rollback segment, but under what conditions, if any, can multiple
> transactions use the same extent in a particular rollback segment?

The rbs segment and extents are always shared. It is at the block level that multiple transactions do not share rbs space.

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Mark D. Powell -- The only advice that counts is the advice that  you follow so follow your own advice --

-----------== Posted via Deja News, The Discussion Network ==---------- http://www.dejanews.com/ Search, Read, Discuss, or Start Your Own Received on Tue Feb 02 1999 - 12:51:45 CST