> >>> Okay that is old version, Ha for me PostgreSQL 12.8 + POSTGIS 3.1.4 this is the newest version any of my servers is running ;) >>> but I think the fixes were done like 6 or 7 years ago such as detailed here: https://www.postgresql.org/message-id/011f01c61653$96c509f0$8300a8c0@trideca p.com
ok thanks >>> As far as if a inner join is always better than a left join, I would say no. For example here is one that showed at least for this use case, a LEFT JOIN was faster: https://towardsdatascience.com/how-we-optimized-postgresql-queries-100x-ff52 555eabe >>> And here where it shows a INNER + UNION ALL was faster than a LEFT https://www.crunchydata.com/blog/postgres-query-optimization-left-join-vs-un ion-all >>> Since you have to update every single parcel anyway, I am curious how something like this would fair: UPDATE parcels p SET (building_count, building_fp) = (select count(*) as num, sum(st_area(b.geom)) as sumarea FROM buildings b on st_intersects(p.geom,st_centroid(b.geom) ) ; >>> Will check and report back Karsten From: postgis-users [mailto:[email protected]] On Behalf Of karsten Sent: Monday, March 27, 2023 6:24 PM To: 'PostGIS Users Discussion' <[email protected]> Subject: Re: [postgis-users] improve query - summarize building count and area on each parcel Regina, >>>> So you had the centroids indexed before you switched to regular join and that took days too? I would expect the index on the centroid to make much more of a difference than the LEFT / INNER JOIN change. No at that time I had not the centroids indexed just the polygon boundaries themselves ... >> I think the LEFT / INNER JOIN performance would have a lot to do with number of rows in each table and whether it resorts to a nested vs. hash. There have been performance issues in PostgreSQL that cause LEFT to be much slower than INNER, but I think most of those have been long resolved. It might be some left over stuff with our poor spatial stats estimates. >>> Interesting >> SELECT version(), postgis_full_version(); shows: PostgreSQL 12.8 (Ubuntu 12.8-0ubuntu0.20.04.1) on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0, 64-bit | POSTGIS="3.1.4 ded6c34" [EXTENSION] PGSQL="120" GEOS="3.10.1-CAPI-1.16.0" PROJ="7.2.1" LIBXML="2.9.10" LIBJSON="0.13.1" LIBPROTOBUF="1.3.3" WAGYU="0.5.0 (Internal)" Cheers Karsten From: postgis-users [mailto:[email protected]] On Behalf Of karsten Sent: Monday, March 27, 2023 5:16 PM To: 'PostGIS Users Discussion' <[email protected]> Subject: Re: [postgis-users] improve query - summarize building count and area on each parcel That worked perfectly: Using just join and setting the index on the centroids geom as well I had the query finish in less than a minute (compared to three day running and not yet finished !) Does anyone have an explanation why 'regular' join is so much faster than 'left join' ? Cheers Karsten ________________________________ From: postgis-users [mailto:[email protected]] On Behalf Of Marcin Mionskowski Sent: Sunday, March 26, 2023 23:34 To: PostGIS Users Discussion Subject: Re: [postgis-users] improve query - summarize building count and area on each parcel In my "explain tests", made on much smaller tables, I get 500 times smaller costs only by changing LEFT JOIN to "regular" JOIN. pon., 27 mar 2023 o 01:07 Raj Talati <[email protected]> napisał(a): I prefer doing insert instead of update if we doing all rows update :) so create New table with new table and copy from old and later drop it you can go without index and do index later after copy. Postgres update is delete and insert internally and direct big update will bloat table. Other thing you can do multi thread if you have 16 core with nothing else can go 12-14 threads updates which can do portion of your big table easy if no good criteria can be mod function on PK Hope this helps . Raj T On Sun, Mar 26, 2023 at 6:54 PM karsten <[email protected]> wrote: Hi All, I have two tables, a parcel (polygon) table and a building (polygon) table in a PostGIS db. There are about 1 million parcels and over a million buildings in these tables ... I have set gist indexes on both and clustered each on a geohash, pkey is set on objectid. I would like to fill 2 additional columns for the parcels layer to have the number of building on each parcel (building_count) and the summed up area of all those building footprints (building_fp). Below is an update query but it is extremely lengthy and inefficient (on a beefy 16 core Ubuntu server with 128 GB tons of RAM) : I had to stop an after running 3 days when it was not finished ... I am wondering if anyone has an idea how to make it more efficient ? This is the query: UPDATE parcels p SET building_count = subquery.num, building_fp = subquery.sumarea from (select objectid, count(*) as num, sum(st_area(b.geom)) as sumarea FROM parcels p left join buildings b on st_intersects(p.geom,st_centroid(b.geom)) group by objectid ) subquery where p.objectid = subquery.objectid ; Any suggestions ? Cheers Karsten Vennemann _______________________________________________ postgis-users mailing list [email protected] https://lists.osgeo.org/mailman/listinfo/postgis-users _______________________________________________ postgis-users mailing list [email protected] https://lists.osgeo.org/mailman/listinfo/postgis-users _______________________________________________ postgis-users mailing list [email protected] https://lists.osgeo.org/mailman/listinfo/postgis-users
