Re: db_file_multiblock_read_count and 10g

From: Syed Jaffar Hussain <sjaffarhussain_at_gmail.com>
Date: Sun, 25 Jan 2009 11:13:53 +0300
Message-ID: <97b7fd2f0901250013q4b9693f7g825b65ed2d1f5a4c_at_mail.gmail.com>

What an odd behavior I have come across when the the value is left for auto tune (on 10gR2), I have observed that the value goes to a higher value and it was causing optimize to favor FTS.

2009/1/25 Greg Rahn <greg_at_structureddata.org>

> 10gR2 introduced Self-Tuning Multiblock Read Count
>
> http://download.oracle.com/docs/cd/B19306_01/server.102/b14214/chapter1.htm#FEATURENO05506
>
> The basic premise is to allow large I/Os for MBRC operations w/o
> giving the Optimizer too much preference to FTS. By default it uses a
> MBRC of 8 for costing, or the system stats MBRC if it is set.
>
> On Sat, Jan 24, 2009 at 4:18 PM, Nuno Souto <dbvision_at_iinet.net.au> wrote:
> > Á¶µ¿¿í wrote,on my timestamp of 25/01/2009 1:44 AM:
> >>
> >> This is called autotuned MBRC - literally, Oracle autotunes the value of
> >> MBRC.
> >
> >
> > I don't think this is the case in 10g. Maybe in 11, but not 10gr2.
> > See this:
> >
> http://download.oracle.com/docs/cd/B19306_01/server.102/b14237/initparams047.htm#CHDFAFHE
> > There is a world of difference between a "default value" and "auto-tune".
> > Nowhere in that doco is it said it is auto-tuned. I do recall reading
> > something from Jonathan about it being so in 11g but I won't be using 11g
> > anytime soon so I can't say for sure.
>
> --
> Regards,
> Greg Rahn
> http://structureddata.org
> --
> http://www.freelists.org/webpage/oracle-l
>
>
>

-- 
Best Regards,

Syed Jaffar Hussain
Oracle Certified Master (10g)
http://www.oracle.com/technology/ocm/shussain.html
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I blog at
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--------------------
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Received on Sun Jan 25 2009 - 02:13:53 CST