| From: | Sandro Santilli <strk(at)keybit(dot)net> |
|---|---|
| To: | Ants Aasma <ants(at)cybertec(dot)at>, Qi Huang <huangqiyx(at)hotmail(dot)com>, heikki(dot)linnakangas(at)enterprisedb(dot)com, josh(at)agliodbs(dot)com, pgsql-hackers(at)postgresql(dot)org, andres(at)anarazel(dot)de, alvherre(at)commandprompt(dot)com, neil(dot)conway(at)gmail(dot)com, daniel(at)heroku(dot)com, cbbrowne(at)gmail(dot)com, kevin(dot)grittner(at)wicourts(dot)gov |
| Subject: | Re: Gsoc2012 idea, tablesample |
| Date: | 2012-04-24 07:31:36 |
| Message-ID: | 20120424073136.GF7891@gnash |
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| Lists: | pgsql-hackers |
On Tue, Apr 24, 2012 at 08:49:26AM +0200, Sandro Santilli wrote:
> On Mon, Apr 23, 2012 at 08:34:44PM +0300, Ants Aasma wrote:
> > SELECT (SELECT reservoir_sample(some_table, 50) AS samples
> > FROM some_table WHERE ctid =~ ANY (rnd_pgtids))
> > FROM random_pages('some_table', 50) AS rnd_pgtids;
>
> But I don't understand the reservoir_sample call, what is it supposed to do ?
Ok got it, that was probably to avoid:
ERROR: more than one row returned by a subquery used as an expression
But this also works nicely:
SELECT * FROM lots_of_points
WHERE ctid = ANY ( ARRAY[(SELECT random_tids('lots_of_points', 100000))] );
and still uses tidscan.
The advanced TID operator would be for random_tids to only return pages rather
than full tids...
--strk;
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