Re: TRANSACTIONS_PER_ROLLBACK_SEGMENT (the real story)

From: Pete Sharman <psharman_at_us.oracle.com>
Date: Tue, 04 Jan 2000 09:30:40 -0800
Message-ID: <38722E40.68A3DABD@us.oracle.com>

The limit Mark talked about was due to some problem which no longer exists (from memory it was something to do with the length of the ROLLBACK_SEGMENTS parameter line in the init.ora file). I know of people who have played around with 2000 rollback segments just to prove it works!

One thing I would suggest is that if only two rollback segments are being used, is there any evidence of waits for the rollback segments? It may be that Oracle is not using any more because it doesn't need to.

Pete

markp7832_at_my-deja.com wrote:

> In article <89o37skkj9a3pqs4gu3ujkbeh0i93dqhpv_at_4ax.com>,
> john v <johnvue_at_gte.net> wrote:
> > On Tue, 4 Jan 2000 08:00:48 +0100, "Sybrand Bakker"
> > <postmaster_at_sybrandb.demon.nl> wrote:
> >
> > >The real story may be higly misleading...
> > >
> > >If you have public rollback segments this parameter will determine
> (based on
> > >the number of processes in init<sid>.ora) how many rollback segments
> are
> > >brought online.
> > >This is, AFAIK, a one-time operation, rollback segments are not added
> > >dynamically.
> > >Hundred segments is outrageous. Oracle has the 'rule of four' which
> means
> > >one rollback segment for every four users, with a minumum of four
> rollback
> > >segments.
> > >
> >
> > I have over 600+ users ... which mathematically works out to 150
> > rollback segments. I really didn't need that many so I cut it down to
> > 100.
> >
> > I've never been a big fan of the "divide by four" rule -- I'd rather
> > go by # of simultaneous transactions at peak times.
> >
> Having 100 rbs segments is excessive. If I remember correctly the
> Oracle ver 7 documentation specifically mentions not exceeding a
> certain number which I think is around 44. I do not remember a limit
> being listed in the ver 8 manual but I suspect that it would be the
> same.

>

> You should determine your number of rbs segments from your number of
> simultaneous transactions like you mentioned. Select count(*) from
> v$transaction several times during peak hours. I bet that your counts
> will be well below 44, much less 100, and since an rbs segment can
> handle multiple transactions at a time you should probably consider
> reducing your number of rbs segments and making your remaining segments
> bigger since I expect that with 100 of them that they are pretty small.

>

> Just my opinion.

>

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

>

> Sent via Deja.com http://www.deja.com/
> Before you buy.

Received on Tue Jan 04 2000 - 11:30:40 CST