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Re: Is it better to set the freelist to a prime number ?

From: Howard J. Rogers <howardjr2000_at_yahoo.com.au>
Date: Tue, 23 Jul 2002 14:19:08 +1000
Message-ID: <ahileg$3s2$1@lust.ihug.co.nz>

"Yong Huang" <yong321_at_yahoo.com> wrote in message news:07b6be7c6105b142172a9b70371d2d92.99975_at_mygate.mailgate.org...
> "Jonathan Lewis" <jonathan_at_jlcomp.demon.co.uk> wrote in message
> news:1026200922.18484.1.nnrp-13.9e984b29_at_news.demon.co.uk
>
> >
> > When a process requests a free list,
> > it uses some sort of 'hashing' function
> > to select which free list, based on the
> > process id. Using a prime number
> > with such mechanisms usually reduces
> > the number of collisions that occur if
> > the input is randomly distributed.
>
> Jonathan, I think you meant non-randomly, or not sufficiently randomly.
> Otherwise why does the prime number matter? But I could be wrong.
>

No, I think he meant randomly.

If the data is of a non-random distribution, then it may well end up 'bunched', whatever you do, and hence you will end up with freelist collisions, whatever you do.

If the data is randomly distributed, then it ought to be possible to work with that data without a free list collision, because you should be able to distribute it across all possible freelists -and being random, it should be equally scattered across all of them. But the use of a non-prime number of freelists, combined with Oracle's hashing algorithm, means that the probability of freelist collisions stays relatively high, even though the nature of the data is such that it shouldn't be.

Regards
HJR
> Yong Huang
>
>
> --
> Posted via Mailgate.ORG Server - http://www.Mailgate.ORG
Received on Mon Jul 22 2002 - 23:19:08 CDT

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