Nyall Dawson 9698444f4a [processing] Fix inefficiencies in Delete Duplicate Geometries algorithm
..and make progress bar more accurate.

Use a spatial index to avoid comparing every feature to every other
feature, and only compare against features with intersecting bounding
boxes instead. Also optimise feature requests and loop logic.

Benchmarks:

Point layer, 6000k features

Before: 30 seconds
After: 0.15 seconds

Point layer, 45k features

Before: > 10 minutes
After: 7 seconds

Fixes #19973
2018-09-29 07:37:53 +10:00
..