Re: Re: Automatic tuning of db_file_multiblock_read_count ???
- From: Peter Alteheld <palteheld@xxxxxxxx>
- To: Jared Still <jkstill@xxxxxxxxx>
- Date: Thu, 14 Jul 2005 09:00:19 +0200 (CEST)
Jared,
it seems the theme I was looking for isn't yet published on that site - it
might be in the upcoming Part 3.
But I have found some stuff in the docs, Perf. Tuning Guide, 14.4:
"In release 10.2, the optimizer uses the value of mbrc when performing full
table scans (FTS). The value of db_file_multiblock_read_count is set to the
maximum allowed by the operating system by default. However, the optimizer uses
mbrc=8 for costing. The "real" mbrc is actually somewhere in between since
serial multiblock read requests are processed by the buffer cache and split in
two or more requests if some blocks are already pinned in the buffer cache, or
when the segment size is smaller than the read size. The mbrc value gathered as
part of workload statistics is thus useful for FTS estimation."
Peter
Jared Still <jkstill@xxxxxxxxx> wrote:The articles by Arup Nanda contain a bit
more detail on this:
http://www.oracle.com/technology/pub/articles/10gdba/index_r2.html
Jared
On 7/13/05, Peter Alteheld <palteheld@xxxxxxxx> wrote:In a future breaking news
(from August 2nd,2005 ;-) Don Burleson lists this as a performance improvement
in 10g R2 - see:
http://dba-oracle.com/oracle_news/2005_8_2_10gr2_performance.htm
I haven't found anything about that in the docs. Has anyone out here more info
about it?
--
Jared Still
Certifiable Oracle DBA and Part Time Perl Evangelist
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