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Have your OSM updates suddenly stopped?

16.03.2017 | Frederik Ramm

bomb_iconIf you’re running a world-wide OSM tile or Nominatim server and you are consuming updates more frequently than once per hour, you might find that your update process got stuck on around 21:00 UTC on March 12, 2017. At that time, a relation (#7066589) was uploaded to OSM that had more than 231-1 members. This is currently allowed by the API, but triggers a failure in the osm2pgsql utility used to update tile server and Nominatim databases. Depending on how your update process is constructed and when it runs, you could be lucky – the relation was deleted 55 minutes later and might therefore never have reached your osm2pgsl. But if your update process is constructed such that it downloads a diff file from OSM and then tries to apply that no matter what, then your process will be stuck because the file containing the large relation can never be successfully applied.

How can I find out if my OSM database is affected?

Your database will not be affected if you do not use the minutely, global updates from OSM. If you use them, you can either check your log files, or look at your database and check if an object created shortly after the problem polygon is there or not. If it is there, then everything is good; if not, then you need to investigate (of course it is possible that your updates are broken for a different reason and maybe for longer).

For a Nominatim database, try this:

nominatim=# select class from place where osm_type=’R’ and osm_id=7066630;
(1 row)

For a tile server database, try this:

osm=# select boundary from planet_osm_polygon where osm_id=-7066630;
(1 row)

In each case, if you don’t get a result back then your database does not include a small boundary relation that was created shortly after the problem relation. (To those who read this long after 16 March 2017, note that the test relation we’re using here could have been changed deleted on OSM meanwhile and that would of course mean it’s normal that it wouldn’t be in your data – check before you panic).

How can I repair the problem?

Nominatim, when run in an update loop with “–import-osmosis-all”, will create a file called “osmosischange.osc” in its data subdirectory, and will try to apply that every time it wakes up from its sleep. Fix the file by removing everything between <relation id="7066589"... and the matching </relation>.

Tile servers will use different ways to update and potentially accumulate changes; one method that we frequently use when setting up servers is to collect un-applied changes in a file named /srv/osm-replicate/var/merged.osc. If you have such a file then both the addition and the deletion of the relation are likely in that file, and you can either delete the relation manually (as described above), or run osmosis --read-xml-change merged.osc --sort-change --simc --write-xml-change sorted.osc && mv sorted.osc merged.osc to squash the relation from the file. If you don’t have such a file, try to find out where your tile server downloads change files to, and get rid of the relation.

Learn more

The issue has led to a patch in osm2pgsql discussed here on GitHub. This patch will make osm2pgsql ignore too-large relations.