Opened 8 years ago

Last modified 8 years ago

#1806 closed defect

Extremely slow and CPU-intensive ST_MakeValid (ST_BuildArea) case — at Version 7

Reported by: strk Owned by: strk
Priority: high Milestone: PostGIS 2.0.1
Component: postgis Version: 2.0.x
Keywords: Cc:

Description (last modified by strk)

The attached shapefile contains a single geometry. A multipolygon composed by a single polygon containing 4213 rings with a total of 82304 vertices.

Passing it as an argument to ST_MakeValid takes forever.

Change History (8)

comment:1 Changed 8 years ago by strk

How does it look in qgis:

No image "offendingline.png" attached to Ticket #1806

comment:2 Changed 8 years ago by strk

It looks like the procedure is stuck within LWGEOM_GEOS_buildArea

comment:3 Changed 8 years ago by strk

Summary: Extremely slow and CPU-intensive ST_MakeValid caseExtremely slow and CPU-intensive ST_MakeValid (ST_BuildArea) case

Yep, confirmed you can hook things forever by calling ST_BuildArea(ST_Boundary(geom))

comment:4 Changed 8 years ago by strk

Owner: changed from pramsey to strk
Status: newassigned

Also memory usage keeps increasing.

Plan: rewrite BuildArea? to avoid all those SymDifference? calls and simply skip polygons fully contained in other polygons (assuming those ones are holes of the other). Should work pretty good and fast...

comment:5 Changed 8 years ago by strk

polygonize finds 3536 polygons, so ST_BuildArea is stuck computing the symdifference between each of them and the aggregated result. While it goes on the time it takes to compute the symdifference grows. It starts with roughly 20 items per second. At iteration 1700 computes ~5 symdifference per second... Every iteration has to rebuild the topology which was already built in the previous iteration.

Changed 8 years ago by strk

Attachment: slowmakevalid.zip added

shapefile with the single offending geometry

comment:6 Changed 8 years ago by strk

Step back: I was completely wrong about how the geometry was rendered. At least, I can't handle to render it that way again. The information about composition is correct.

comment:7 Changed 8 years ago by strk

Description: modified (diff)
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