[OSM-dev] Cacheing map data between API and JOSM

[John Smith]

2009/10/13 Tomáš Kouba <t.kouba at gmail.com>:
> Hello,
>
> I have an idea how to dramatically fasten building a map in JOSM. Currently
> if you want to update your maps via JOSM then it has to download the whole
> map every time which is very slow. So it would be great if JOSM would
> download only diferrences in map.
>
> Suggested solution:
> Create a "cacher" (sort of proxy server) probably located on localhost,
> which would store and cache your maps. Cacher would stand between JOSM and
> map server API (see http://files.chciwww.cz/OSM_Components.png). You could
> use caching feature just by specifying this "cache server" as a map server
> in JOSM. Cacher would have its own map database and if you wanted cacher to
> get you a map up-to-date, cacher would download from main map server only
> differences in map.
>
> How come this feature isn't already implemented as it looks so important? Or
> is there a some sort of "tack", that kills attemps to cache maps?
>
> I'm new to Open Street Map project so my apologies if I'm missing something.
> Reason for my contribution is that I'm looking for a subject of my
> bachelor's thesis and this looks useful.

JOSM already caches WMS tiles so it's not a great leap that it would
be able to cache OSM data as well, the only problem would be telling
the OSM API you only want data for a given area that is newer than X
date, even your suggestion of a proxy wouldn't fair any better without
help from the API side of things.

The big problem with caching data is ensuring it's up to date but also
complete consistent with what the DB server sees.