BUG #6275: Horrible performance regression

The following bug has been logged online:

Bug reference: 6275
Logged by: Finlay Thompson
Email address: finlay(at)dragonfly(dot)co(dot)nz
PostgreSQL version: 8.4.9
Operating system: Ubuntu 11.04
Description: Horrible performance regression
Details:

After an upgrade from 8.4.8 to 8.4.9 performance of load script went from ~
3 hours to not finishing after 24 hours.

Context: We have a continuous build script, that loads, grooms, matches data
every few hours. The script has been run over 100 times in the last few
weeks, and has steadily been taking around 3 hours. It is really a group of
scripts, something like 15000 lines of sql, and some python scripts to run
it together.

After upgrading the postgresql*-8.4 packages on ubuntu, to version 8.4.9,
the script suddenly stopped working, and consuming all the ram (16GB) on the
computer (i7).

I spent about a day trying to diagnose the problem, with some help from
#postgresql, and ran through the script step by step, but was unable to find
any specific issue.

Today I reinstalled the 8.4.8 version, and it built the database in 3:02
hours, as before.

From this, I reckon something is broken in the 8.4.9 release.

I would love to isolate the problem, and am happy to try anything people
suggest.

Sorry I can't be more specific about the problem, but I thought I should
report the issue.

btw: The database uses plpython and postgis.

Regards,
Finlay Thompson