Re: #pages read per I/O?

Hi Y

Just to expand on what Howard has said.

If you perform a read via a conventional index read, then Oracle will only read in one block per I/O regardless of the DFMRC.

If you perform a Full Table/Index Scan, Oracle will attempt to read in DFMRC of blocks per I/O. However, what Oracle asks and expects and what the O/S is able to deliver could be two quite different things. Check out Steve Adams site for a script that determines what the "real" value of your multiblock read is http://www.ixora.com.au

V$FILESTAT as Howard has suggested and the report from STATSPACK provides statistics of blocks per read and occurrences of index reads vs. full table reads.

Cheers

Richard

"Howard J. Rogers" <howardjr2000_at_yahoo.com.au> wrote in message news:KI2q9.51535$g9.149794_at_newsfeeds.bigpond.com...
> Just a semantic aside, but we don't talk 'pages' in Oracle, but 'blocks'.
> And hence the parameter that governs how many blocks are read in a single
> I/O is called db_file_multiblock_read_count.
>
> Type 'show parameter db_file' in sql plus, and you'll see what it's set
to.
>
> As for an average, have a look at v$filestat.
>
> Regards
> HJR
>
>
> "y" <y_at_y.com> wrote in message news:3DA8B29F.9635C9DA_at_y.com...
> > I am using Oracle8i EE.
> > I found only Oracle Server process can read index/data pages into Buffer
> > Cache. So that means at least Oracle8i EE didn't support asynchronous
> > read, right?
> > I want to know when the Oracle Server process need to do read from the
> > disk, how many pages it can read into Buffer Cache one I/O? How to check
> > the average number of read pages per I/O?
> > TIA
> >
>
>
Received on Sat Oct 12 2002 - 21:21:47 CDT