Postgres 8.4 - Table size inflates

[david harel]

Greetings,

Using Postgres v-8.4 for 3 years already, I now face a situation where one
single table inflates enormously.
Before vacuum the size was 1.5 GB for the table and 0.5 GB for the indexes.

I tried to run CHECKPOINT in plsql (that's all I understood from reading:
http://www.depesz.com/2011/07/14/write-ahead-log-understanding-postgresql-co
nf-checkpoint_segments-checkpoint_timeout-checkpoint_warning/)

After full vacuum and reindex the table reduces it's size to 23MB and
indexes reduce to 44MB.

Typical usage of the table is insert.
We never delete anything off that table and rarely we update it.
Also we get key violations due to bad input also on rare occasions.
Also we recently upgraded the hardware (OS (ubuntu 10.4 server eddition)
runs on a virtual machine, copy to new hardware was using virtual machines
snapshot).
I don't know where to begin the investigation on the topic.

Thanks.