how to plan for vacuum?

Hi,

For I can not find too much information about how to use vacuum, I want
to ask some general information about the guideline of vacuum planning.

1. How do we know if autovacuum is enough for my application, or should
I setup a vacuum manually from cron for my application?

2. How to set the GUC parameters for autovacuum?
There are two sets of parameters for autovacuum:
- vacuum threshold and scale factor (500/0.2)
　 - analyze threshold and scale factor(250/0.1)
Is there any guideline to set these parameters? When does it need to
change the default values?
　
3. How to tune cost-based delay vacuum?
I had searched in performance list; it seems that most of the practices
are based on experience / trial-and-error approach to meet the
requirement of disk utilization or CPU utilization. Is there any other
guild line to set them?

For when autovacuum is turned on by default, if the parameters for
vacuum have not been set well, it will make the system rather unstable.
So I just wonder if we should setup a section in the manual about the
tips of vacuum, then many users can easily set the vacuum parameters for
their system.

Best Regards
Galy Lee
NTT OSS Center