From: | Jochem van Dieten <jochemd(at)oli(dot)tudelft(dot)nl> |
---|---|
To: | vernonw(at)gatewaytech(dot)com |
Cc: | pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Is a better way to have the same result of this query? |
Date: | 2002-12-05 22:05:57 |
Message-ID: | 3DEFCDC5.9050906@oli.tudelft.nl |
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Lists: | pgsql-performance |
Vernon Wu wrote:
> 12/5/2002 1:06:03 PM, Jochem van Dieten <jochemd(at)oli(dot)tudelft(dot)nl> wrote:
>
>>You start by using a dataset of realistic size. Sorry, but if the actual
>>time is < 10.00 ms it is rather pointless to optimize further since
>>chance is going to be the biggest factor. And the IN/EXISTS difference
>>is dependent on dataset size.
>
> Do you mean that using "EXIST" is not necessary out-perform using 'IN" even the "explain" say so? What is the right
> size for those two key words?
IIRC, IN might be faster on small datasets, but EXISTS is faster on big
ones. So you have to optimize with a dataset that resembles the actual
dataset you will be using in production as close as possible. I don't
know what the size is at which one gets faster as the other.
Jochem
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