Re: ASM parameters

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.

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