[OSM-dev] osm2pgsql deltas

[Frederik Ramm]

Hi,

Steve Hill wrote:
> I'm just exceptionally dubious about stuffing minutely deltas directly 
> into osm2pgsql

I would not recommend that either. The Osmosis process is *really* very 
elegant and takes all the responsibility of finding out where you are, 
what you need to get etc. away from you, it may be worth trying to get 
it to work. The process produces one single diff that you can then apply 
with osm2pgsql.

> it to catch up using only minutely deltas seems a recipe for disaster 
> because my experience is that applying minutely deltas has a significant 
> overhead when compared to daily deltas.

Yes, it surely has, because after the diff has been applied, the node 
geometries for all affected ways will be rebuilt. If you have a long way 
and someone takes his time refining it over the course of 30 minutes, 
you may incur 30 geometry updates when working with minutely diffs, vs. 
only one when working with one.

So even if you manually download a daily and a few hourly diffs to get 
you where you want to be, it makes sense to combine them into one 
*before* applying them. Osmosis does that for you with

osmosis --rxc 1.osc --rxc 2.osc --mc --wxc merged.osc

But note that the new replication diffs may contain the same object 
multiple times, so it is always good to add a --simc which will then 
drop everything but the latest version.

Bye
Frederik