Re: Max IO size

Kevin Brand wrote:
>
> I'm not sure whether you can set ( increase ) it. You can at least find out
> what Oracle *thinks* it is by setting db_file_multiblock_read_count to some
> ridiculously large number, start the instance and then check the value in
> the SGA.
>
> On my platform, with and 8k block size, I cannot set
> db_file_multiblock_read_count larger than 8. Well, that is, I can, but the
> SGA reports it at 8 regardless.
>
> -Kevin
>
> "Christian Lang" <clang_at_mediaprint.at> wrote in message
> news:6cf185c9.0109060439.4a285df7_at_posting.google.com...
> > "Kevin Brand" <kevin.brandx_at_tel.gte.com> wrote in message
> news:<9n63cl$926$1_at_news.gte.com>...
> > > Check that your multiblock_read_count setting didn't get truncated to an
> OS
> > > limit. If you set it to 64, which would mean "64 8k blocks to be read
> in a
> > > multiblock read", you'd look for a 512k read. However, if the OS limit
> is
> > > 256k reads, then Oracle would truncate multiblock_read_count to 32 (
> based
> > > on your 8k block size ).
> > >
> > > Take a look at the setting in the SGA to make sure it matches your
> init.ora
> > > setting, as Oracle will quietly set it to the platform specific max
> value.
> > >
> > > -Kevin
> > > "Connor McDonald" <connor_mcdonald_at_yahoo.com> wrote in message
> > > news:3B966E0C.3BA_at_yahoo.com...
> > > > I've got a sun (solaris 2.8) box with with datafiles under vxfs.
> After
> > > > setting
> > > >
> > > > - maxphys to 512k
> > > > - vxiomax to 512k
> > > > - db block size to 8k
> > > > - multiblock read count to 64
> > > >
> > > > I had presumed that I could get a ceiling of half a meg per read on
> > > > (say) a full table scan, but a level 8 10046 trace yields a ceiling of
> > > > 256k (ie p3 in the waits is 32 not 64)
> > > >
> > > > I'll be repeating the test under a raw partition tomorrow but comments
> > > > anyone ? As a related question, anyone know what Oracle's SSTIOMAX is
> > > > under the various versions (say from 7.3)
> > > >
> > > > Cheers
> > > >
> > > > --
> > > > ==============================
> > > > Connor McDonald
> > > >
> > > > http://www.oracledba.co.uk
> > > >
> > > > "Some days you're the pigeon, some days you're the statue..."
> >
> > Hi,
> > I'm running on Solaris 2.6 and Oracle 817 and I have a lot of
> > "direct path read/write" waits.
> > I think that it can be concerned with the
> > db_file_multiblock_read_count and OS Max I/O.
> >
> > Where can I detect the current Value of Max I/O on the OS and how can
> > I set it.
> >
> > thanks a lot
> > Chris

Appears to be a file system restriction. The same test on a *raw* vxvm volume can get up to 1m (with maxphys and vxiomax at 1m, multiblock-read-count at 128 on block size 8k). But smack a file system on top of it and ker-bang, I'm back down to 256k...

Yet *another* reason why I like raw and hate file systems !

Cheers
Connor

-- 
==============================
Connor McDonald

http://www.oracledba.co.uk

"Some days you're the pigeon, some days you're the statue..."