RE: Rollback segments - Is it better to have 2 or 10 extents

Hi Jonathan,

I've just checked this at 8.1.5, and multiple transactions can write into the same extent concurrently. I've also just checked some old dumps that I have from 7.2, and the same was true then. In fact, I don't think that this argument for more extents in a rollback segment has been valid since 7.0 at least.

Maybe a better argument for more than 2 extents in a rollback segment is the proportion of undo available for the construction of consistent read images immediately after a wrap - for 2 extents it is only 50% of capacity, whereas for 10 extents it is 90%.

Regards,
Steve Adams

http://www.ixora.com.au/

http://www.oreilly.com/catalog/orinternals/

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-----Original Message-----
From:	Jonathan Lewis [SMTP:jonathan_at_jlcomp.demon.co.uk]
Sent:	Thursday, October 21, 1999 9:09 AM
To:	comp.databases.oracle.server_at_list.deja.com
Subject:	Re: Rollback segments - Is it better to have 2 or 10 extents

The reason why 2 extents is bad is that a transaction that starts in one extent and crosses into the second extent makes the entire rollback segment unavailable for any other transaction to start. (True up to 7.3, but I haven't checked it for 8.0, 8.1).

10 is better because this denial of access still leaves 8 extents for other transactions to start in.

 Sent via Deja.com http://www.deja.com/  Before you buy. Received on Sat Oct 23 1999 - 22:58:11 CDT