[OSM-dev] Postgres 8.4 performance trouble in osm2pgsql setup

Frederik Ramm frederik at remote.org
Thu May 6 22:12:28 BST 2010


Hi,

    I had posted about performance problems with Postgres 8.4 in 
September last year already. With Ubuntu Lucid just released, which 
comes with 8.4 by default, I played around some more. Unfortunately I am 
still a little bit away from having systematic, comparable results, but 
I have the impression that importing updates with osm2pgsql is somehow 
buggy (performance-wise) in 8.4.

I'm running this on a machine with SSD. With 8.3, the process was 
disk-bound despite SSD, which is what I would expect, after all there's 
not much to compute.

With 8.4, a (large, ~ 1 day) test diff takes about four times as long to 
load. This is unacceptable and I will probably have go back to 8.3 
because of that until I can find out exactly what the problem is.

When searching for possible reasons on the web, I found this message 
about Postgres 9.0 and irregularities with intarray index usage:

http://osdir.com/ml/pgsql-hackers/2010-03/msg01035.html

It could have *something* to do with what I am seeing, however I could 
not reproduce intarray operations being slower from within a function 
than from the command line.

I'll investigate this further and report back with anything I find; for 
the time being just be warned that there are isolated indications of 
Postgres 8.4 being less suitable for OSM than 8.3. (I am largely 
ignorant of any changes between 8.3 and 8.4, and simply set my config 
options to the same I had been using with 8.3; it is possible that 8.4 
requires something to be configured differently to work.)

I'd also be interested to hear from anyone who, despite this message, 
plays with 8.4 (or even 9.0 alpha) and has something to say.

Bye
Frederik

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




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