Re: Script to compute random page cost

OK, what you are seeing here is that for your platform the TESTCYCLES
size isn't enough; the numbers are too close to measure the difference.

I am going to increase the TESTCYCLES from 5k to 10k. That should
provide better numbers.

---------------------------------------------------------------------------

Oliver Elphick wrote:
> On Mon, 2002-09-09 at 07:13, Bruce Momjian wrote:
> >
> > OK, turns out that the loop for sequential scan ran fewer times and was
> > skewing the numbers. I have a new version at:
> >
> > ftp://candle.pha.pa.us/pub/postgresql/randcost
>
> Latest version:
>
> olly(at)linda$
> random test: 14
> sequential test: 11
> null timing test: 9
> random_page_cost = 2.500000
>
> olly(at)linda$ for a in 1 2 3 4 5
> > do
> > ~/randcost
> > done
> Collecting sizing information ...
> random test: 11
> sequential test: 11
> null timing test: 9
> random_page_cost = 1.000000
>
> random test: 11
> sequential test: 10
> null timing test: 9
> random_page_cost = 2.000000
>
> random test: 11
> sequential test: 11
> null timing test: 9
> random_page_cost = 1.000000
>
> random test: 11
> sequential test: 10
> null timing test: 9
> random_page_cost = 2.000000
>
> random test: 10
> sequential test: 10
> null timing test: 10
> Sequential time equals null time. Increase TESTCYCLES and rerun.
>
>
> Available memory (512M) exceeds the total database size, so sequential
> and random are almost the same for the second and subsequent runs.
>
> Since, in production, I would hope to have all active tables permanently
> in RAM, would there be a case for my using a page cost of 1 on the
> assumption that no disk reads would be needed?
>
> --
> Oliver Elphick Oliver(dot)Elphick(at)lfix(dot)co(dot)uk
> Isle of Wight, UK
> http://www.lfix.co.uk/oliver
> GPG: 1024D/3E1D0C1C: CA12 09E0 E8D5 8870 5839 932A 614D 4C34 3E1D 0C1C
> ========================================
> "Draw near to God and he will draw near to you.
> Cleanse your hands, you sinners; and purify your
> hearts, you double minded." James 4:8
>
>

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Bruce Momjian | http://candle.pha.pa.us
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