Re: Multi-Block read count

Svend Jensen wrote:
>
> Norman Dunbar wrote:
>
> > Morning all,
> >
> > my first question of 2002 ...
> >
> > Quote from Guy Harrison in Oracle SQL High-Performance Tuning :
> >
> > "On Windows NT/Win2k the maximum number of blocks that can be read
> > cannot exceed 128K for 32 bit versions,
> > On most versions of Unix when the I/O is through a filesystem, no more
> > than 8K can be read in one physical I/O,
> > On Unix when the datafiles are locvated on raw devices, the maximum I/O
> > rate varies from 64K (earlier versions of Solaris) to 1MB (latest
> > version of HP-UX."
> >
> > So the question I have is, how do I find out what the maximum number of
> > Oracle blocks that I can read in one single OS I/O read is ?
> >
> > Regards,
> > Norman.
> >
> > ------------------------------------------------------------------------
> > -----
> > Norman Dunbar EMail: Norman.Dunbar_at_LFS.co.uk
> > Database/Unix administrator Phone: 0113 289 6265
> > Fax: 0113 289 3146
> > Lynx Financial Systems Ltd. URL: http://www.Lynx-FS.com
> > ------------------------------------------------------------------------
> > -----
> >
> >
>
> The trick with show parameter is nice, but I cant believe the figures I
> get. At work on a IBM e-server 250 Win2K Oracle 8.1.7EE with hardware
> 4M raid controler and seven mirrors striped, I've set dfmrc to 32384,
> set event 10046, level 12 and ran a large full scans. Acording to the
> trace file 'scattered read' p3 (blocks) never got any higher than 128.
> At 8k block that makes 1M.
> Tried the show parameter at my home system, win2K, Oracle 8.1.7EE and I
> got 256. Havent tried the trace yet.
> But same OS, oracle version and different results - better on ide disk
> than 160scsi. Hard to believe.
>
> A way to make sure, restart database, set high dfmrc, run some large
> full scans and then check v$filestat against some disk io OS monitor.
> If the figures are close to one another, then the requested block reads
> from oracle to the os-layer is OK. If it is in the nabourhood of 1:n,
> then one oracle request for x blocks is turned into n times x OS disk io's.
>
> I tried that on Sun solaris 6 some time ago. Solaris read only 7 blocks
> of 8k in one io cycle. With default setup, no fiddling.
>
> Somebody got a tool for win2k to measure OS disk io's like iostat?
>
> /Svend Jensen

Oracle also has an internal maximum SSTIOMAX which varies from platform to platform, but on most 8i+, the limitation is 1m.

hth
connor

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

http://www.oracledba.co.uk

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