Re: ASM parameters
Date: Fri, 25 Jan 2008 20:23:30 -0600
Message-ID: <yQwmj.5469$Rg1.1117@nlpi068.nbdc.sbc.com>
"Mladen Gogala" <mgogala_at_yahoo.com> wrote in message
news:479a386e$0$1341$834e42db_at_reader.greatnowhere.com...
> On Fri, 25 Jan 2008 03:43:42 -0800, Charles Hooper wrote:
>
>> I don't use ASM, but there may be some hints provided in "Cost-Based
>> Oracle Fundamentals" to explain what you are seeing. Paraphrased from
>> that book:
>> Oracle uses MBRC from the SYS.AUX_STATS$ 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.
>>
>> You might also want to take a look at the following regarding the
>> DB_FILE_MULTIBLOCK_READ_COUNT parameter:
>> http://jonathanlewis.wordpress.com/2007/05/20/system-stats-strategy/
>
> Charles, ASM is a physical layer, volume manager in user space. I am
> just trying to increase the read-ahead to speed up backups. ASM cache
> is very much like file system cache, not like the DB cache. I am afraid
> that CBO doesn't have much to do with it.
> This would be analogous to increasing the block size of the underlying
> file system.
>
Well, that's what you get when turning a RDBMS into a volume manager -
awkwardness.
Oracle likes to think that database can be a all-purpose software.
Received on Fri Jan 25 2008 - 20:23:30 CST