| From: | Bruno Wolff III <bruno(at)wolff(dot)to> |
|---|---|
| To: | Michael Contzen <Michael(dot)Contzen(at)dohle(dot)com> |
| Cc: | pgsql-sql(at)postgresql(dot)org |
| Subject: | Re: How slow is distinct - 2nd |
| Date: | 2002-10-04 15:31:08 |
| Message-ID: | 20021004153108.GA14180@wolff.to |
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| Lists: | pgsql-sql |
On Tue, Oct 01, 2002 at 14:18:50 +0200,
Michael Contzen <Michael(dot)Contzen(at)dohle(dot)com> wrote:
> Here the table:
>
> mc=# \d egal
> Table "public.egal"
> Column | Type | Modifiers
> --------+---------+-----------
> i | integer |
>
> mc=# select count(*) from egal;
> count
> ---------
> 7227744
> (1 row)
>
> mc=# select count(distinct i) from egal;
> count
> -------
> 67
> (1 row)
This suggests that the best way to do this is with a hash instead of a sort.
If you have lots of memory you might try increasing the sort memory size.
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