Generally I try monitor v$filestat to see what proportion of IO is due to rollback...The ideal is of course nil, but to do so pretty much means giving everyone a couple of dozen 1555's every day :-)
So you end up with the balancing act of trying to make them as small as possible without introducing 1555's hth connor --- Doug C <[EMAIL PROTECTED]> wrote: > Thanks.. makes sense... > Can I use x$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 <[EMAIL PROTECTED]> 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: [EMAIL PROTECTED] > >> > >> Fat City Network Services -- (858) 538-5051 > FAX: > >> (858) 538-5051 > >> San Diego, California -- Public Internet > >> access / Mailing Lists > >> > >-------------------------------------------------------------------- > >> To REMOVE yourself from this mailing list, send > an > >> E-Mail message > >> to: [EMAIL PROTECTED] (note EXACT spelling of > >> 'ListGuru') and in > >> the message BODY, include a line containing: > UNSUB > >> ORACLE-L > >> (or the name of mailing list you want to be > removed > >> from). You may > >> also send the HELP command for other information > >> (like subscribing). > > > >===== > >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: [EMAIL PROTECTED] > > Fat City Network Services -- (858) 538-5051 FAX: > (858) 538-5051 > San Diego, California -- Public Internet > access / Mailing Lists > -------------------------------------------------------------------- > To REMOVE yourself from this mailing list, send an > E-Mail message > to: [EMAIL PROTECTED] (note EXACT spelling of > 'ListGuru') and in > the message BODY, include a line containing: UNSUB > ORACLE-L > (or the name of mailing list you want to be removed > from). You may > also send the HELP command for other information > (like subscribing). ===== 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: [EMAIL PROTECTED] Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
