On Tue, Apr 17, 2012 at 04:29:52PM -0400, Stephen Frost wrote: > Josh, > > * Josh Berkus (j...@agliodbs.com) wrote: > > FWIW, the PostGIS folks would *really* love to have a TABLESAMPLE which > > worked with geographic indexes. This would be tremendously useful for > > constructing low-resolution "zoom out" tiles on maps and similar. > > I'm familiar with the concept of 'zoom out' tiles and PostGIS, but I > don't actually see the connection between that and TABLESAMPLE. Perhaps > I'm missing something, but I've never seen a case where you create 'zoom > out' tiles by just grabbing some portion of the data at random, as that > would end up creating empty spots or missing pieces.
Actually a random sample would really be representative of the data distribution. What the type analyzer gets is a sample and that sample is what the estimator looks at to answer the question: How many rows fall in this rectangle ? You can see how well it works by passing your queries using && operator to "EXPLAIN ANALYZE" and compare estimated/real. I'm looking for a way to fetch random samples these days so I confirm the need for a quick way to fetch the same sample that "analyze" command fetches but at SQL level. --strk; ,------o-. | __/ | Delivering high quality PostGIS 2.0 ! | / 2.0 | http://strk.keybit.net - http://vizzuality.com `-o------' -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers