Re: Gsoc2012 idea, tablesample

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_pointsWHERE 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...

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