[OSM-dev] osm2pgsql tile expiry freaks me out

[Frederik Ramm]

Hi,

    I'm trying to work with the tile expiry list produced by osm2pgsql 
but something seems to be very wrong there. Last night's daily diff, for 
example, had 459 MB; about 2.3 million objects were changed. The 
corresponding osm2pgsql tile expiry list for zoom level 18 (done with -e 
18-18) has 5.6 GB and claims to mark dirty a whopping 350 million 
objects. That would mean that one changed object, on average, touches 
more than 100 tiles on zoom level 18.

I'm running an update every 15 minutes on another server, and there I 
get the following, equally strange results:

date/time       tiles expired   # of changed objects
----------------------------------------------------
2009-11-04 14:30    7469596      20022
2009-11-04 14:45     792306      19125
2009-11-04 15:00  158804709      17155
2009-11-04 15:30    7092126      33276
2009-11-04 16:00     500746      47315
2009-11-04 16:15     226193      65182
2009-11-04 16:30   61437040      94737
2009-11-04 16:45   96680596      46008
2009-11-04 17:00    2195996     111912
2009-11-04 17:15    1459539      63360
2009-11-04 17:30     585327      51517
2009-11-04 17:45    4452958      27274
2009-11-04 18:00    1927180      60348
2009-11-04 18:15   90720429      23879

As you can see, the average number of edits in a 15-minute window is 
around 50k, but the number of expired tiles varies wildly beyond belief.

I did fix two bugs regarding tile expiry recently, one of which, I 
believe, could have caused larger than normal bounding boxes to be 
expired, but while the daily numbers cited above stem from before the 
fix while the 15-minutely are from a fixed version, so that doesn't seem 
to make a difference.

(All numbers above refer to a planet-wide database.)

I'm in the process of instrumenting osm2pgsql to find out what changes 
generate these huge tile lists but maybe someone has a hunch.

Bye
Frederik

-- 
Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00'09" E008°23'33"