Best ways around memory Error on large st_union for overlay processing

[Paul Ramsey]

> On Jan 15, 2026, at 9:46 AM, Mike Treglia <mtreglia at gmail.com> wrote:
> 
> Is there an obvious or more optimal way to do that st_union(st_exteriorring(geom)) step for large datasets? 
> 

Just spitballing…

Starting with an ST_Subdivide on all the rings, writing out the ring segments and a unique key into a staging table.
Then do the st_union on a gridded basis. I think that should be safe?
The part I worry about is doing the polygon building, unless you do the build with overlapping grid cells to select potential input ring segments, and then post-filter the polygon collection you get to remove any overlapping/duplicated polygons. My concern is that a very large input polygon relative to the grid size might fail to be built, if all its component pieces do not happen to fall into a single grid cell.
At some point you end up building something of the scale and complexity of the topology module, and maybe you would be able to get some good results starting there instead.
P.
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