Re: MBRC & db_file_multiblock_read_count

From: Charles Hooper <hooperc2000_at_yahoo.com>
Date: Thu, 17 Jan 2008 03:51:54 -0800 (PST)
Message-ID: <d444fd00-9841-47e8-b5d7-85ad9af1ad1a@i29g2000prf.googlegroups.com>


On Jan 17, 5:53 am, "Yannick ROGER" <yannick.ro..._at_achatpro.com> wrote:
> Hi,
>
> I'm working on Oracle 10g.
>
> What is the diffrence between:
> - MBRC setted by dbms_stats.set_system_stats or automaticly with
> dbms_stats.GATHER_SYSTEM_STATS
> and
> - db_file_multiblock_read_count setted in int file?
>
> Is the scope of these 2 parameters the same?
> Is one override the other?
> Do i have to set the same value for both of them?
>
> Can you recommend a good doc about this?
>
> Regards,
>
> Yannick

Paraphrased from "Cost-Based Oracle Fundamentals": Oracle uses MBRC from the SYS.AUX_STATS$ for cost calculations, but the runtime engine tries to use DB_FILE_MULTIBLOCK_READ_COUNT when performing physical reads. On Start up, Oracle determines the operating system's largest physical read size and silently uses that to limit whatever value is set for DB_FILE_MULTIBLOCK_READ_COUNT.

I believe that Jonathan Lewis now recommends not setting (or at least experimenting with not setting) the DB_FILE_MULTIBLOCK_READ_COUNT parameter. See:
http://jonathanlewis.wordpress.com/2007/05/20/system-stats-strategy/

Charles Hooper
IT Manager/Oracle DBA
K&M Machine-Fabricating, Inc. Received on Thu Jan 17 2008 - 05:51:54 CST

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