[postgis-users] diffrent execution plan on Postgres 9.5 and Postgres 11 for ST_union and performance problem Postgres 11

[Martin Davis]

Well, we have figured out what the problem is - it's a known regression in
the GEOS UnaryUnion code, reported in this ticket [1]

Unfortunately there's no fix for this yet, but we'll try and escalate this.

[1] https://trac.osgeo.org/geos/ticket/867

On Thu, Apr 11, 2019 at 11:07 AM Martin Davis <mtnclimb at gmail.com> wrote:

>
>
> On Thu, Apr 11, 2019 at 3:27 AM Lars Aksel Opsahl <Lars.Opsahl at nibio.no>
> wrote:
>
>> Can it be problem related ST_Union and aggregate ?
>>
>
> Can you test the performance of aggregate ST_Union on it's own by dropping
> the GROUP BY and instead using a WHERE clause to union a small-ish subset
> of the geometries?  (But large enough to give a measurable query time.)
>
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