Generally I try monitor v$filestat to see what
proportion of IO is due to rollback...The ideal is of
course nil, but to do so pretty much means giving
everyone a couple of dozen 1555's every day :-)
So you end up with the balancing act of trying to make
them as small as possible without introducing 1555's
hth
connor
- Doug C <dcowles_at_i84.net> wrote: > Thanks.. makes
sense...
> Can I use x$bh or something to determine whether
> it's nicely squeezed into the
> buffer at some point in time?
>
>
> On Mon, 12 Nov 2001 02:00:21 -0800, you wrote:
>
> >If rb's are small, then there is a good chance that
> >just when they are about to aged out of the buffer
> >cache, hey presto! another session needs them again
> -
> >so you end up with a nice scenario where they spend
> >their life in the cache and cause virtually no IO.
> >
> >As they get larger and larger, the
> time-before-reuse
> >time gets longer and longer - which will mean more
> and
> >more IO. Its the same for having lots of extents -
> >many moons ago this used to be due to txns needing
> >their own extents. Oracle lifted this restriction
> >somewhere in v7, but it still makes sense to have
> 20
> >or so extents, because then when a rollback segment
> >increases in size, it does it in nice 5% increments
> -
> >keeping the probability of it all fitting in the
> cache
> >high.
> >
> >hth
> >connor
> >
> > --- Doug C <dcowles_at_i84.net> wrote: > OK.. this
> may
> >be a little naive..and maybe I'm just
> >> jogging my own memory, but
> >> here it goes...
> >> There are a couple schools of thought on rollback
> >> segments as near as I can
> >> figure. Some like to set optimal, and some
> don't.
> >> The one's that don't like
> >> to shrink them at night or once daily or some
> other
> >> variation..
> >>
> >> Question: Why bother? If they get big and you
> have
> >> the room, so what? They
> >> won't have to extend tomorrow, no? If you're
> >> concerned about space, why not set
> >> a good maxextents or a limit on the filesize..
> >>
> >> What's the problem with them getting large?
> >>
> >> Thanks,
> >> Doug
> >>
> >>
> >>
> >>
> >> --
> >> Please see the official ORACLE-L FAQ:
> >> http://www.orafaq.com
> >> --
> >> Author: Doug C
> >> INET: dcowles_at_i84.net
> >>
> >> Fat City Network Services -- (858) 538-5051
> FAX:
> >> (858) 538-5051
> >> San Diego, California -- Public Internet
> >> access / Mailing Lists
> >>
>
>--------------------------------------------------------------------
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> >=====
> >Connor McDonald
> >http://www.oracledba.co.uk (mirrored at
> >http://www.oradba.freeserve.co.uk)
> >
> >"Some days you're the pigeon, some days you're the
> statue"
> >
> >__________________________________________________
> >Do You Yahoo!?
> >Everything you'll ever need on one web page from
> News and Sport to Email and Music Charts
> >http://uk.my.yahoo.com
> >--
> >Please see the official ORACLE-L FAQ:
> http://www.orafaq.com
>
> --
> Please see the official ORACLE-L FAQ:
> http://www.orafaq.com
> --
> Author: Doug C
> INET: dcowles_at_i84.net
>
> Fat City Network Services -- (858) 538-5051 FAX:
> (858) 538-5051
> San Diego, California -- Public Internet
> access / Mailing Lists
>
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> (or the name of mailing list you want to be removed
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> also send the HELP command for other information
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Connor McDonald
http://www.oracledba.co.uk (mirrored at
http://www.oradba.freeserve.co.uk)
"Some days you're the pigeon, some days you're the statue"
Do You Yahoo!?
Everything you'll ever need on one web page from News and Sport to Email and Music
Charts
http://uk.my.yahoo.com
--
Please see the official ORACLE-L FAQ: http://www.orafaq.com
--
Author: =?iso-8859-1?q?Connor=20McDonald?=
INET: hamcdc_at_yahoo.co.uk
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Received on Mon Nov 12 2001 - 09:41:29 CST
