[OSM-dev] Incomplete diffs?

[Frederik Ramm]

Hi,

On 11/07/2011 02:24 AM, marqqs at gmx.eu wrote:
> # normal diff
> $ zcat 20111103-20111104.osc.gz |grep -c "timestamp=\"2011-11-03T12:"
> 58968
>
> # replication diff
> $ cat 1103-1104.osc |grep -c "timestamp=\"2011-11-03T12:"
> 59068
>
> And yes, I thought on cumulating the version in the second file before I started counting with grep.

I think you may have found a bug in Osmosis' --simplify-change 
algorithm. (Or, if you created the above 1103-1104.osc file yourself, 
you have re-implemented a bug already present in Osmosis.)

Both the normal diff and the daily diff are correct as far as I can see, 
but the simplified version that you created - the one with 59068 
elements - is not.

An object created earlier on that particular day and deleted between 
12:00 and 13:00 will not show up in the normal daily diff:

$ zgrep -A1 -B1 '<node id="1490162262"' 20111103-20111104.osc.gz
$

It will show up twice in the replication diff, once for creation and 
once for deletion:

$ zgrep -A1 -B1 '<node id="1490162262"' 1103-1104.osc.gz
     <node id="1490162261" version="1" timestamp="2011-11-03T08:09:48Z" 
uid="419929" user="hoti" changeset="9728137" lat="47.4399545" 
lon="16.4376938"/>
     <node id="1490162262" version="1" timestamp="2011-11-03T08:09:48Z" 
uid="547666" user="Igor Kurvanor" changeset="9728123" lat="45.7510611" 
lon="6.2813975"/>
   </create>
   <delete>
     <node id="1490162262" version="2" timestamp="2011-11-03T12:42:36Z" 
uid="547666" user="Igor Kurvanor" changeset="9730094" lat="45.7510611" 
lon="6.2813975"/>
   </delete>
$

Now if such a replication diff is simplified with Osmosis, in my opinion 
it should drop the node altogether, but what it does is it always keeps 
the highest version even if that corresponds to a deletion that 
counteracts a previous creation:

$ osmosis -q --read-xml-change 1103-1104.osc.gz --simc 
--write-xml-change - | grep -A1 -B1 '<node id="1490162262"'
   <delete>
     <node id="1490162262" version="2" timestamp="2011-11-03T12:42:36Z" 
uid="547666" user="Igor Kurvanor" changeset="9730094" lat="45.7510611" 
lon="6.2813975"/>
   </delete>
$

Now this is a minor bug because I don't know any consumer that will trip 
on a deletion request for a non-exisitng object but still it is a 
behaviour that I would not have expected. Anyway, it should explain the 
discrepancy you are seeing.

Bye
Frederik