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Hi</div>
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Thanks a lot for your help everybody.</div>
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Lars</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> postgis-users <postgis-users-bounces@lists.osgeo.org> on behalf of Martin Davis <mtnclimb@gmail.com><br>
<b>Sent:</b> Thursday, April 11, 2019 10:03 PM<br>
<b>To:</b> PostGIS Users Discussion<br>
<b>Subject:</b> Re: [postgis-users] diffrent execution plan on Postgres 9.5 and Postgres 11 for ST_union and performance problem Postgres 11</font>
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<div>Well, we have figured out what the problem is - it's a known regression in the GEOS UnaryUnion code, reported in this ticket [1]</div>
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<div>Unfortunately there's no fix for this yet, but we'll try and escalate this.</div>
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<div>[1] <a href="https://trac.osgeo.org/geos/ticket/867">https://trac.osgeo.org/geos/ticket/867</a></div>
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<div dir="ltr" class="x_gmail_attr">On Thu, Apr 11, 2019 at 11:07 AM Martin Davis <<a href="mailto:mtnclimb@gmail.com">mtnclimb@gmail.com</a>> wrote:<br>
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<div dir="ltr" class="x_gmail_attr">On Thu, Apr 11, 2019 at 3:27 AM Lars Aksel Opsahl <<a href="mailto:Lars.Opsahl@nibio.no" target="_blank">Lars.Opsahl@nibio.no</a>> wrote:</div>
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Can it be problem related ST_Union and aggregate ?</div>
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<div>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.)</div>
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