Doubt regarding HQApi metricdata command

[dvd_debian]

Hi,

I am using Hyperic HQ open source edition, Version 4.2.0.7 on BOSS(A Debian Derived Linux ) with postgres as the database.

I have installed hyperic server and agent successfully.
My requirement is to get ,

System Availability
Total Disk Space
Disk Space Used

I visited this url,

http://support.hyperic.com/display/DOC/HQApi+metricdata+command

to get the metric data from the database.

I am able to get the Metric data but its showing only todays data(Time Format and Value)(ie.) its showing metric data related to the date of usage of the HQAPI.

I need to get the past values also (Say the start date and time when the agent reported the Hyperic Server).
For this what I need to do?

Also one doubt.
does Hyperic server deleted old values(Metric data collected ) from database.?

Can any one please help me..

or
else is there any way to get these metric data directly from
database?
for this what tables and columns , I need to use.

Thanks in advance,
Sri