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From John Haxby <...@scalix.com>
Subject Re: Optimizing indexes with mulitiple processors?
Date Fri, 10 Jun 2005 07:21:46 GMT
Chris Collins wrote:

>Ok that part isnt surprising.  However only about 1% of 30% of the merge was
>spent in the OS.flush call (not very IO bound at all with this controller).
>  
>
On Linux, at least, measuring the time taken in OS.flush is not a good 
way to determine if you're I/O bound -- all that does is transfer the 
data to the kernel.   Later, possibly much later, the kernel will 
actually write the data to the disk.

The upshot of this is that if the size of the index is around the size 
of physical memory in the system, optimizing will appear CPU bound.   
Once the index exceeds the size of physical memory, you'll see the 
effects of I/O.   OS.flush will still probably be ver quick, but you'll 
see a lot of I/O wait if you run, say, top.

jch

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