id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
20633	[Patch]Download object: Too slow when downloading a relation with members with OSM api	GerdP	team	"==== What steps will reproduce the problem?
1. Download a complex relation like [osmwww:relation/9488835 r9488835] with members to a new layer (not using overpass)
2. Watch how it takes some seconds to actually download all the data and much more time to process it before a the rendered data is shown.
3. Save to *.osm file 
4. Load from *.osm file

==== What is the expected result?
It should take more or less the same time to process the downloaded data as it takes to open the file.
==== What happens instead?
The downloaded data takes much longer. 
==== Please provide any additional information below. Attach a screenshot if possible.
I used VisualVM to monitor the program and found that a lot of time is spent in DatasetMerger.fixReferences(). It turned out that the data that is retrieved with the 1st call
{{{
2021-03-21 08:44:43.115 INFO: GET https://api.openstreetmap.org/api/0.6/relations?relations=9488835 -> HTTP/1.1 200 (322 ms)
2021-03-21 08:44:53.634 INFO: GET https://api.openstreetmap.org/api/0.6/relation/9488835/full -> HTTP/1.1 200 (10.0 s)
}}}
is causing the trouble. The result of the call is the incomplete relation. This incomplete data is stored in field `MultiFetchServerObjectReader.outputDataSet` and later, all the detailed data is merged with this incomplete relation. This forces lots of rather slow `QuadBucketPrimitiveStore.reindexRelation()`
calls. This merging isn't really needed, the only reason for the initial download is to find out if the relation exists. 
{{{
URL:https://josm.openstreetmap.de/svn/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2021-03-17 18:58:40 +0100 (Wed, 17 Mar 2021)
Build-Date:2021-03-17 17:59:56
Revision:17580
Relative:URL: ^/trunk

Identification: JOSM/1.5 (17580 en) Windows 10 64-Bit
OS Build number: Windows 10 Home 2004 (19041)
Memory Usage: 412 MB / 3641 MB (221 MB allocated, but free)
Java version: 1.8.0_221-b11, Oracle Corporation, Java HotSpot(TM) 64-Bit Server VM
Look and Feel: com.sun.java.swing.plaf.windows.WindowsLookAndFeel
Screen: \Display0 1920×1080 (scaling 1.00×1.00)
Maximum Screen Size: 1920×1080
Best cursor sizes: 16×16→32×32, 32×32→32×32
VM arguments: [-XX:StartFlightRecording=name=MyRecording2,settings=d:\dbg\gerd.jfc, -XX:FlightRecorderOptions=defaultrecording=true,dumponexit=true,dumponexitpath=e:\ld\perf_20210321_082504.jfr]
}}}
"	enhancement	closed	normal	21.03	Core	tested	fixed	template_report performance	Don-vip simon04