Re: Indexing for geographic objects?
От | Oleg Bartunov |
---|---|
Тема | Re: Indexing for geographic objects? |
Дата | |
Msg-id | Pine.GSO.3.96.SK.1001208220018.4174f-100000@ra обсуждение исходный текст |
Ответ на | Re: Indexing for geographic objects? (Tom Lane <tgl@sss.pgh.pa.us>) |
Список | pgsql-hackers |
On Fri, 8 Dec 2000, Tom Lane wrote: > Date: Fri, 08 Dec 2000 12:59:27 -0500 > From: Tom Lane <tgl@sss.pgh.pa.us> > To: Oleg Bartunov <oleg@sai.msu.su> > Cc: selkovjr@mcs.anl.gov, 'pgsql-hackers ' <pgsql-hackers@postgresql.org> > Subject: Re: [HACKERS] Indexing for geographic objects? > > Oleg Bartunov <oleg@sai.msu.su> writes: > >> 5000 looks like a suspiciously round number ... how many rows are in > >> the table? Have you done a vacuum analyze on it? > > > about 10,000 rows, > > So the thing is estimating 0.5 selectivity, which is a fallback for > operators it knows nothing whatever about. > > [ ... digs in Selkov's scripts ... ] > > CREATE OPERATOR @ ( > LEFTARG = seg, RIGHTARG = seg, PROCEDURE = seg_contains, > COMMUTATOR = '~' > ); > > CREATE OPERATOR ~ ( > LEFTARG = seg, RIGHTARG = seg, PROCEDURE = seg_contained, > COMMUTATOR = '@' > ); > > Sure 'nuff, no selectivity info attached to these declarations. > Try adding > > RESTRICT = contsel, JOIN = contjoinsel > > to them. That's still an entirely bogus estimate, but at least > it's a smaller bogus estimate ... small enough to select an indexscan, > one hopes (see utils/adt/geo_selfuncs.c). Great ! Now we have better plan: test=# explain select * from test where s @ '1.05 .. 3.95'; NOTICE: QUERY PLAN: Index Scan using test_seg_ix on test (cost=0.00..61.56 rows=100 width=12) EXPLAIN > > I have not dug through Gene's stuff to see which other indexable > operators might be missing selectivity estimates, but I'll bet there > are others. If you have the time to look through it and submit a > patch, I can incorporate it into the version that will go into contrib. > We didn't look at Gene's stuff yet. Maybe Gene could find a time to check his code. > regards, tom lane > _____________________________________________________________ Oleg Bartunov, sci.researcher, hostmaster of AstroNet, Sternberg Astronomical Institute, Moscow University (Russia) Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/ phone: +007(095)939-16-83, +007(095)939-23-83
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