[postgis-users] defending postgresql - postgis.

[Frederik Ramm]

Hi,

Paragon Corporation wrote:
> OpenStreetMap also runs on PostgreSQL now too (had switched from MySQL),
> though I don't think they run on PostGIS. 

Correct; details about the server running core OSM database is here: 
http://wiki.openstreetmap.org/wiki/Servers/smaug

This server does not even make use of PostgreSQL's two-dimensional 
indexes; stores points with integer values for lat/lon and computes a 
"bucket" id for each point so that they can be retrieved quickly through 
an one-dimensional index. This is a left-over from the time when someone 
running the OSM backend would have a choice between using MySQL and 
PostgreSQL and nobody saw the need to fix it.

> Of course PostGIS  enjoys preferential treatment as far as if you want to
> load OpenStreetMap data into it.  I don't think the tools for other
> databases compares.

That is slightly misleading; there are tools to load OSM data into a 
PostgreSQL database like the one used on the central server, but there 
are *also* tools that will populate a PostGIS table from OSM data, 
optimised for rendering. This comes with a loss of parts of the data 
(and topology) which are not needed for drawing maps.

Details about the server at OSM HQ that runs the PostGIS database for 
map rendering here: http://wiki.openstreetmap.org/wiki/Servers/yevaud

For those really interested, you can even go up one step in the Wiki 
hierarchy and access Munin graphs that tell you something about the 
database use. If any of you PostgreSQL buffs spot something in there 
that looks fishy, let us know ;)

Bye
Frederik

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