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Re: Multi-Block read count

From: Connor McDonald <connor_mcdonald_at_yahoo.com>
Date: Wed, 09 Jan 2002 19:50:38 +0000
Message-ID: <3C3C9F0E.38A6@yahoo.com>


Niall Litchfield wrote:
>
> "Herman de Boer" <h.de.boer_at_itcg.nl> wrote in message
> news:bde5777e.0201090629.78036153_at_posting.google.com...
> > hello Norman,
> >
> > it is platform dependent. The method I use in order to determine the
> > maximum in a database is simple, using sqlplus:
> > * alter session set db_file_multiblock_read_count = 10000;
> > * show parameters db_file_multiblock_read_count
> >
> > On my NT laptop, with RDBMS 9.0.1, db_file_multiblock_read_count can
> > be set to 64, so with 8 Kb block size, at most 512 Kbyte can be read.
>
> snip
>
> from a compaq server we have
>
> SQL> alter session set db_file_multiblock_read_count = 10000;
>
> Session altered.
>
> SQL> show parameter multiblock;
>
> NAME TYPE VALUE
> ------------------------------------ ------- --------------------
> db_file_multiblock_read_count integer 128
> hash_multiblock_io_count integer 0
> sort_multiblock_read_count integer 2
>
> suggesting that it might be hardware specific as well - this is an nt4
> server. Nice trick though.
>
> --
> 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
>
> ******************************************

Its also worth nothing that the ceiling on multiblock read count is what *Oracle* thinks that it will be able to achieve. Its quite possible that you will not be able to get that due to other restrictions...

For example, Oracle on Solaris can get up to 1m, but unless you set maxphys kernel parameter you won't get near that.

To see what you can actually get, set a 10046 trace at level 8 and run a full scan on a big table. The p3 values in the trace file for the scattered reads shows you what Oracle could achieve in reality.

hth
Connor

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

http://www.oracledba.co.uk

"Some days you're the pigeon, some days you're the statue..."
Received on Wed Jan 09 2002 - 13:50:38 CST

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