id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
17819	Improve performance when loading or validating complex multipolygon relation	GerdP	team	"Someone created a real monster : https://www.openstreetmap.org/relation/9427189
More than 30_000 ways and + 1 Mio nodes. While writing this ticket it was deleted.
It takes quite long to load this relation even when it is stored in pbf format.
One major bottleneck is the method `Multipolygon.joinWays()` which frequently modifies a list of nodes. In current JOSM this list is an instance of `CopyList`, and `CopyList` doesn't implement `addAll()` and thus calls add() in a loop.
Another problem is that the collecion wayids is stored as a list. This collection is often searched like this: `getWayIds().contains(p.getUniqueId())` which is fast enough for the typically small lists but slow for these monsters."	enhancement	closed	normal	19.06	Core		fixed	multipolygon performance