[postgis-users] ST_ConcaveHull performance issue

[Darafei "Komяpa" Praliaskouski]

Hi,

There were changes ST_ConcaveHull that fixed robustness of it in 2.2 -> 2.5
chain.
To point where the penalty comes from, try to run a query and on a side
console server-side run `sudo perf top`. Function names will get you a
rough idea where the execution process lives now.

To further debug, go to blame view in github and try updating
st_concavehull (it's in SQL) change by change. Most recent adds an union
here, try commenting it out and hot reloading on your db.
https://github.com/postgis/postgis/blame/svn-trunk/postgis/postgis.sql.in#L6155

Can you share the data and ticket this on http://trac.osgeo.org/postgis/?

What is the data structurally? Are these 6000 objects points, or polygons?


On Fri, Aug 2, 2019 at 3:43 AM Trevor Wiens <tsw.web at gmail.com> wrote:

> I am having difficulty determining why I'm seeing significant differences
> in performance between two database configurations with the same data.
>
> One one machine (centos) I have the following software:
> geos 3.5.0
> sfcgal 1.3.1
> cgal 4.7.1
> postgis 2.2
> postgresql 9.4
>
> On a second machine (debian 10) I have the following:
> geos 3.7.1
> sfcgal 1.3.6
> cgal 4.13
> postgis 2.5.2
> postgresql 9.6
>
> In terms of hardware there is no significant difference, if anything the
> second machine is more capable, but that is not reflected in my performance
> results.
>
> On the first machine when I run a ST_ConcaveHull with about 6000 features,
> I get result a second or two. On the second machine, it won't finish within
> 30 minutes. Both are using geos as the postgis.backend. I don't understand
> why the one is so much faster than the other with the identical data and
> query.
>
> Any suggestions as to what to what the cause may be or how I might
> diagnose the cause?
>
> Any clues would be greatly appreciated.
>
> TSW
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-- 
Darafei Praliaskouski
Support me: http://patreon.com/komzpa
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