Thanks, Gregory and Simon, for the very useful posts.
I have increased the vacuum_cost_limit to 2000 for now, just to see if
that has an impact. Hopefully positive.
Next on my list is to be able to easily upgrade to 8.3, but Slony
seemed like a daunting task the last time I tried. I am on 8.2.9, on
Linux CentOS. Is there a quick and reliable guide to upgrading,
without causing a downtime in a high production environment?