Re: rollback segments, why two extents?

Jonathan,

A follow-up to your reply, also posted to the News Group for others.

Within the concepts guide just before
file:/G|/ORANT/ORA815/doc/server.815/a67781/c02block.htm#4860 (substitute your URL directory structure) "The first transaction that needs to acquire more rollback space checks the next extent of the rollback segment. If the next extent of the rollback segment does not contain information from an active transaction, Oracle makes it the current extent, and all transactions that need more space from then on can write rollback information to the new current extent."

Is it this check that means Oracle requires two extents. The fact that Oracle does not want to go and allocate another extent automatically.

The document goes on
"As the transactions continue writing and fill the current extent, Oracle checks the next extent already allocated for the rollback segment to determine if it is available."

So is Oracle actually preempting the transaction and saying, since I have already needed to grow, I'll check to see if the next extent is available, prior to actually needing it?

Hopefully Thomas Kyte can give us the definitive answer for tomorrow <GGG>
Andrew

Jonathan Gennick wrote:

> Can anyone fill me in on exactly why rollback segments need
> to have at least two extents? I thought that there was an
> interested reason for this, related to the way Oracle uses
> these segments. I remember reading something on that once,
> but I can't find it now.
>
> thanks,
>
> Jonathan
Received on Sun May 02 1999 - 23:33:49 CDT