| From: | Ron Mayer <rm_pg(at)cheapcomplexdevices(dot)com> |
|---|---|
| To: | Gregory Stark <stark(at)enterprisedb(dot)com> |
| Subject: | Re: [GENERAL] Autovacuum Improvements |
| Date: | 2007-01-22 20:17:39 |
| Message-ID: | 45B51BE3.9050809@cheapcomplexdevices.com |
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| Thread: | |
| Lists: | pgsql-general pgsql-hackers |
Gregory Stark wrote:
>
> Actually no. A while back I did experiments to see how fast reading a file
> sequentially was compared to reading the same file sequentially but skipping
> x% of the blocks randomly. The results were surprising (to me) and depressing.
> The breakeven point was about 7%. [...]
>
> The theory online was that as long as you're reading one page from each disk
> track you're going to pay the same seek overhead as reading the entire track.
Could one take advantage of this observation in designing the DSM?
Instead of a separate bit representing every page, having each bit
represent 20 or so pages might be a more useful unit. It sounds
like the time spent reading would be similar; while the bitmap
would be significantly smaller.
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