Re: Redo Log Positioning

Ed Stevens <Ed.Stevens_at_nmm.nissan-usa.com> schreef in berichtnieuws 8end9q$rjo$1_at_nnrp1.deja.com...
> In article <957288168.15447.0.pluto.d4ee154e_at_news.demon.nl>,
> "Sybrand Bakker" <postbus_at_sybrandb.demon.nl> wrote:
> > IMO you have no other choice than to place the redologs on one raid 1
 disk,
> > and the hard- or software mirror on the other raid 1 disk.
> > As the redolog files are written sequentially there is no performance
 hit in
> > placing all three on one drive. I usually start with 4 redo log
 groups, this
> > layout seems less troublesome.
> >
> > Hth,
> >
> > Sybrand Bakker, Oracle DBA
> >
> > <rogerxb_at_my-deja.com> schreef in berichtnieuws
> > 8emjtg$t78$1_at_nnrp1.deja.com...
> > > I currently have two redo log files, unmirrored and sized at 2M
 each.
> > > When we see intense processing there is a slow down and the error
 log
> > > indicates that the bottleneck is the redo logs; they are unable to
> > > complete archiving quickly enough when switching from redo 1 to
 redo 2.
> > >
> > > So I realize I have to re-work the system to at least increase the
 size
> > > of the logs, and therefore switch less frequently.
> > >
> > > Here's my question.
> > >
> > > I have 5 physical 9.1 Gig drives - split into two raid sets -
> > > 2 * 9.1 Gig Raid 1 and
> > > 3 * 9.1 Raid 5.
> > > The current redo logs are placed one on each of these separate
> > > devices.
> > > I understand that my Raid 5 is going to be slower when writing the
> > > logs, but what I want to know is - how should I lay out my log
 files?
> > > I believe The theoretical best is to have three groups with two
> > > mirrored members in each, across at least three devices; but I only
> > > have two physical devices and one is quicker than the other ......
 any
> > > suggestions ??
> > > Should I just increase the size of my logs, and allow the operating
> > > system to do all the mirroring ???
> > >
> > > Cheers
> > > Rog
> > >
> > >
> > > Sent via Deja.com http://www.deja.com/
> > > Before you buy.
> >
> >
>
> While the writing from one log to the next is sequential, if you place
> them on the same physical device (regardless of any RAID or logical
> partitioning) wouldn't there be contention as one log file is being
> written while the previous one is being read for archive? Of course,
> this assume archive logmode.
>
> --
> Ed Stevens
> (Opinions are not necessarily those of my employer)
>
>
> Sent via Deja.com http://www.deja.com/
> Before you buy.

You would be right when you have only 2 redo log groups. Having three or more minimizes the chance this happens. Say you have 3 online redo log files, only if the third file fills, archiving will occur, and this is a single action, so the contention should be short, instead of continuous. I agree there are situations with occasional 'bursts' of activity, when all online redolog files fill at the same time. IMO: you need to adjust the size of your redo log files to prevent this happens.

Regards,

Sybrand Bakker, Oracle DBA Received on Tue May 02 2000 - 00:00:00 CDT