Postgresql – why use PostgreSQL clusterdb instruction

I do not have all information for pointing to the source of your problem, but I think you should create your postgresql cluster in a different way. Instead of using the postgresql generic command pg_ctl, you should use the Debian/Ubuntu provided command pg_createcluster. This way you will have a working setup that survives reboot, you may specify your data directory and your log directory, you may also specify the start policy in order to activate it automatically on boot. And you may use all cluster commands: pg_lsclusters, pg_upgradecluster, and so on.

Every cluster uses three directories:

• /etc/postgresql/8.4/CLUSTERNAME, for its configuration
• your data directory, for all your data and WAL (default /var/lib/postgres/8.4/CLUSTERNAME)
• your log directory, for your logs (default /var/log/postgresql)

Rows in postgresql have no fixed order. Not only are records placed where ever there is free space records can also move around. This is because when a row is updated a new version of the row is created in a new location while the old version continues to live in it's old location until it's removed by vacuum.

A CLUSTER operations sorts all rows but does indeed not affect how postgresql add's rows. So the data won't stay sorted. However postgresql keeps statistics among which is the correlation for each column between the order of the rows in the tables and the sorted order of that column. So the planner can still optimize it's plan based on the statistics that tell it the table is still mostly sorted even if some rows have been added after a cluster operation (or have been moved by updates).