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From Knut Anders Hatlen <knut.hat...@oracle.com>
Subject Re: Parameters related to Seek Time in a Hard Disk
Date Wed, 14 Sep 2011 10:48:08 GMT
Code Guy <isurulucky@gmail.com> writes:

> Hi all,
>
>
> I went through the StoreCostController implementation to get an idea
> of the estimated costs for store/fetch operations. 
>
> public static final double BASE_CACHED_ROW_FETCH_COST = 0.17;
> public static final double BASE_UNCACHED_ROW_FETCH_COST = 1.5;
> public static final double BASE_GROUPSCAN_ROW_COST = 0.12;
> public static final double BASE_NONGROUPSCAN_ROW_FETCH_COST = 0.25;
> public static final double BASE_HASHSCAN_ROW_FETCH_COST = 0.14;
> public static final int STORECOST_CLUSTERED = 0x01;
> public static final int STORECOST_SCAN_SET      = 0x01;
> public static final int STORECOST_SCAN_NORMAL   = 0x02;
>
> I want to reduce the cost allocated to seek operations for
> a particular test. Can anyone specify which of these costs are related
> to the seek time?

Hi Isuru,

I think BASE_UNCACHED_ROW_FETCH_COST is the one you're looking for, as
it's meant to represent the time it takes to fetch a page from disk into
the page cache.

The costs haven't been updated for quite some time now, and they would
probably benefit from adjustment both for faster CPUs and for the
increased popularity of solid-state disks with short search times.

-- 
Knut Anders

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