I have a 8.4 database (installed on ubuntu 10.04 x86_64). It holds Zabbix database. The database on disk takes 10Gb. SQL dump takes only 2Gb. I've gone through
http://archives.postgresql.org/pgsql-general/2008-08/msg00316.php and got some hints. Naturally, the biggest table is history (the second biggest is history_uint. Together they make about 95% of total size). I've tried to perform CLUSTER on it, but seemed to be taking forever (3 hours and still not completed). So I cancelled it and went with database drop and restore. It resulted in database taking up 6.4Gb instead of 10Gb. This is a good improvement, but still isn't quite what I expect. I would appreciate some clarification.