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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Igor,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>The stats estimation for PostGIS has always been not the greatest. It’s more of a limitation with PostgreSQL as I understand it.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>It’s been getting better over the years though. Even in the best case scenario only the bounding box estimation would happen and Paul may be better able to answer what happens with the functions such as ST_Contains (which use the Function instrumentation).<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>So a better test to confirm your stats are working correctly is an && test which I have below.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>I’m running PostgreSQL 15.1, compiled by Visual C++ build 1914, 64-bit POSTGIS="3.3.2 3.3.2" [EXTENSION] PGSQL="150" GEOS="3.11.1-CAPI-1.17.1" SFCGAL="SFCGAL 1.4.1, CGAL 5.3, BOOST 1.78.0" PROJ="7.2.1" GDAL="GDAL 3.4.3, released 2022/04/22" LIBXML="2.9.9" LIBJSON="0.12" LIBPROTOBUF="1.2.1" WAGYU="0.5.0 (Internal)" TOPOLOGY RASTER<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>explain analyze select * from test where ST_GeomFromText('POLYGON((0 0,3 -0,3 3,0 3,0 0))') && p;<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>which give me the expected answer of – <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Seq Scan on test (cost=0.00..1.06 rows=1 width=32) (actual time=0.019..0.024 rows=4 loops=1)<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'> Filter: ('010300000001000000050000000000000000000000000000000000000000000000000008400000000000000080000000000000084000000000000008400000000000000000000000000000084000000000000000000000000000000000'::geometry && p)<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'> Rows Removed by Filter: 1<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Planning Time: 0.131 ms<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Execution Time: 0.046 ms<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>And 4 rows are indeed returned for me.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>explain analyze select * from test where ST_GeomFromText('POLYGON((50 0,52 0,52 2,50 2,50 0))') && p;<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Seq Scan on test (cost=0.00..1.06 rows=1 width=32) (actual time=0.022..0.024 rows=1 loops=1)<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'> Filter: ('01030000000100000005000000000000000000494000000000000000000000000000004A4000000000000000000000000000004A4000000000000000400000000000004940000000000000004000000000000049400000000000000000'::geometry && p)<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'> Rows Removed by Filter: 4<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Planning Time: 0.124 ms<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Execution Time: 0.047 ms<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>I confirm that I get the same answer of below when doing<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>explain analyze select * from test where ST_Contains(ST_GeomFromText('POLYGON((0 0,3 -0,3 3,0 3,0 0))') , p);<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Seq Scan on test (cost=0.00..126.05 rows=1 width=32) (actual time=0.026..0.038 rows=4 loops=1)<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'> Filter: st_contains('010300000001000000050000000000000000000000000000000000000000000000000008400000000000000080000000000000084000000000000008400000000000000000000000000000084000000000000000000000000000000000'::geometry, p)<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'> Rows Removed by Filter: 1<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Planning Time: 0.132 ms<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Execution Time: 0.061 ms<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>So it does seem odd to me that ST_Contains would give a higher estimate than the && operation. That could be a bug in the function instrumentation of ST_Contains and ST_Intersects.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Thanks,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'>Regina<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D'><o:p> </o:p></span></p><div style='border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt'><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>From:</span></b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> postgis-users [mailto:postgis-users-bounces@lists.osgeo.org] <b>On Behalf Of </b>Igor ALBUQUERQUE SILVA<br><b>Sent:</b> Thursday, December 1, 2022 4:37 AM<br><b>To:</b> postgis-users@lists.osgeo.org<br><b>Subject:</b> [postgis-users] Row estimations<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><div><div><div><p class=MsoNormal>Hello everyone,<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>I have a question regarding the row estimations/gist indexes. Here's a minimal reproduction of it:<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>create table test(p geometry(point));<br>insert into test(p) values (st_makepoint(1,1));<br>insert into test(p) values (st_makepoint(1,2));<br>insert into test(p) values (st_makepoint(2,1));<br>insert into test(p) values (st_makepoint(2,2));<br>insert into test(p) values (st_makepoint(51,1));<br>analyze test;<br>explain analyze select * from test where ST_Contains(ST_GeomFromText('POLYGON((0 0,3 -0,3 3,0 3,0 0))'), p);<br>explain analyze select * from test where ST_Contains(ST_GeomFromText('POLYGON((50 0,52 0,52 2,50 2,50 0))'), p);<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>The two queries get the same cost/row estimation, of 1 row. This is the EXPLAIN ANALYZE of the first query:<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Seq Scan on test (cost=0.00..126.05 rows=1 width=32) (actual time=0.015..0.022 rows=4 loops=1)<br> Filter: st_contains('01030000000100000005000000000000000000F0BF000000000000F0BF0000000000000040000000000000F0BF00000000000000400000000000000040000000000000F0BF0000000000000040000000000000F0BF000000000000F0BF'::geometry, p)<span style='color:#500050'><br> Rows Removed by Filter: 1<br></span> Planning Time: 0.072 ms<br> Execution Time: 0.035 ms<br>(5 rows)<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>What I was expecting is the first query to estimate 4 rows and the second to estimate 1, like what I get If I try the same thing using integers.<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>create table test(x integer, y integer);<br>insert into test(x, y) values (0, 0);<br>insert into test(x, y) values (0, 1);<br>insert into test(x, y) values (1, 0);<br>insert into test(x, y) values (1, 1);<br>insert into test(x, y) values (50, 0);<br>analyze test;<br>explain analyze select * from test where x between 0 and 1 and y between 0 and 1;<br>explain analyze select * from test where x between 50 and 51 and y between 0 and 1;<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>My question is: is this expected behaviour? I actually have a much larger table with a gist index where I found this occurring, and this causes the planner to make bad decisions: every query that I do will have the same estimation, and whenever this estimation is very wrong, the planner does not take the optimal decision when it has to compare with other indexes costs in a more complicated query.<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>I'm using the official docker image, PostgreSQL 15.1 (Debian 15.1-1.pgdg110+1) on x86_64-pc-linux-gnu, compiled by gcc (Debian 10.2.1-6) 10.2.1 20210110, 64-bit POSTGIS="3.3.1 3786b21" [EXTENSION] PGSQL="150" GEOS="3.9.0-CAPI-1.16.2" PROJ="7.2.1" LIBXML="2.9.10" LIBJSON="0.15" LIBPROTOBUF="1.3.3" WAGYU="0.5.0 (Internal)" TOPOLOGY<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Best regards,<o:p></o:p></p></div><div><p class=MsoNormal>Igor<o:p></o:p></p></div></div></div></div></div></body></html>