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

[Martin Davis]

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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