You might well find it worth your while having a browse at steve adams
excellent site at www.ixora.com.au
--
Niall Litchfield
Oracle DBA
Audit Commission UK
*****************************************
Please include version and platform
and SQL where applicable
It makes life easier and increases the
likelihood of a good answer
******************************************
"vrw" <linux4me2000_at_netscape.net> wrote in message
news:9udkrh$ghg$1_at_news8.svr.pol.co.uk...
> Vladimir M. Zakharychev wrote:
>
> > Simply because Oracle does not operate with small files, thus it does
not
> > need them to be aggregated (the obvious exclusion is BFILE which is
stored
> > outside the db). Internally Oracle operates on blocks of raw data
(that's
> > why raw devices provide so far the best performance - they don't have
any
> > fs-related alignment/chunking of data as well as fs-level caching
> > overhead). These blocks are cached in the buffer cache which resides in
> > RAM thus eliminating the need to perform physical I/O altogether once
the
> > block is read into buffer cache and until it is purged. On well
designed,
> > programmed and configured Oracle dbs logical to physical I/O ratio
should
> > be 10/1 or better (that is, buffer cache hit ratio should be at least
> > 90%). Such ratios make FS read performance fairly insignificant as at
all
> > times at least 9/10 of all data blocks are cached and do not require
> > physical disk reads. Of course, write performance should also be good,
> > especially for redo log devices, but I don't see how any fs in
particular
> > may help speeding up disk writes as effectively as your disk array
> > hardware cache buffer :) To sum up: file systems are designed to store
and
> > retrieve files effectively, but Oracle's not about files - it's about
> > structured data. Files are employed just because they are the common
mean
> > for storing data and almost all operating systems provide similar
abstract
> > interfaces for operating them. Yet the best I/O performance in Oracle is
> > achieved on raw devices where no file systems get in the way.
> >
> > Correct me if I'm wrong at any point.
> >
> Vladimir:
>
> That makes sense ! I wasn't aware how Oracle handled its data internally.
> Since they do it how you described, it makes sense that FS performance
does
> not have much of a say in the whole affair...
> Thanks for a great response !
>
> Volkmar
>
Received on Mon Dec 03 2001 - 03:28:24 CST
