On 01.09.2011 12:23, Alexander Korotkov wrote:
On Thu, Sep 1, 2011 at 12:59 PM, Heikki Linnakangas< heikki.linnakan...@enterprisedb.com> wrote:So I changed the test script to generate the table as: CREATE TABLE points AS SELECT random() as x, random() as y FROM generate_series(1, $NROWS); The unordered results are in: testname | nrows | duration | accesses -----------------------------+**-----------+-----------------+**---------- points unordered buffered | 250000000 | 05:56:58.575789 | 2241050 points unordered auto | 250000000 | 05:34:12.187479 | 2246420 points unordered unbuffered | 250000000 | 04:38:48.663952 | 2244228 Although the buffered build doesn't lose as badly as it did with more overlap, it still doesn't look good :-(. Any ideas?But it's still a lot of overlap. It's about 220 accesses per small area request. It's about 10 - 20 times greater than should be without overlaps.
Hmm, those "accesses" numbers are actually quite bogus for this test. I changed the creation of the table as you suggested, so that all x and y values are in the range 0.0 - 1.0, but I didn't change the loop to calculate those accesses, so it still queried for boxes in the range 0 - 100000. That makes me wonder, why does it need 220 accesses on average to satisfy queries most of which lie completely outside the range of actual values in the index? I would expect such queries to just look at the root node, conclude that there can't be any matching tuples, and return immediately.
-- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
