| From: | Martijn van Oosterhout <kleptog(at)svana(dot)org> |
|---|---|
| To: | Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> |
| Cc: | Gregory Stark <stark(at)enterprisedb(dot)com>, nikolay(at)samokhvalov(dot)com, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: mal advice in FAQ 4.1. |
| Date: | 2007-10-09 19:30:59 |
| Message-ID: | 20071009193059.GE8062@svana.org |
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| Lists: | pgsql-hackers |
On Tue, Oct 09, 2007 at 06:40:23PM +0200, Pavel Stehule wrote:
> It needs always seq scan :(, and take space on buffer cache. Solution
> based on random generated PK are much faster. I collaborate with one
> my customer. He shows random products from 10K products on every page
> of one eShop. And he cannot understand, so ORDER random() LIMIT is bad
> trick, because this trick is on PostgreSQL FAQ.
It's the only trick that works in all situations though. There are
ofcourse faster methods, but they require information about the
distribution of the values, the type, PKs, indexes etc...
The standard does have stuff relating to extracting samples from
tables, but they're not implemented.
Have a nice day,
--
Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
> From each according to his ability. To each according to his ability to litigate.
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