Re: Max IO size

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