[hobbit] Hobbit Average Data

[Henrik Stoerner]

Hi Phil,

On Tue, Nov 27, 2007 at 03:08:22PM +0900, Phil Wild wrote:
> I'll ask a question first, what is it that is wrong with the current
> implementation. If the "people" want the ability to zoom into a five
> minute period from a year back, then you need to modify the rrd files.

Good question.

There's really nothing wrong with the current implementation, but it
does have some limitations. You *can* tune the RRD definitions to save
more 5-minute measurements, or store MIN/MAX values (in fact, the
snapshots have had the capability for some time to configure the RRD 
file layout so you don't have to dig into the C code).

The main limitation is that RRD will *always* normalize data. It is
quite rare for updates to happen exactly at 300 second intervals, and
when they are slightly off then RRD will not store the raw data;
instead, it will compute what the value probably would have been, if the
measurement had happened exactly at the 300-second mark. So you really
cannot get the exact measurements (the observed data) from the RRD
files.

In most cases this doesn't matter since the differences are small, and
measurements do happen roughly at the "right" time. But it is something
you should consider when trying to tap into the Hobbit measurements.


The main reason I added this was because it would allow users an easy 
hook into the raw data that Hobbit collects. The data that is fed into 
the RRD files is extremely standardized, as opposed to most of the other 
data available in Hobbit. So if you do want to add some custom processing 
of monitoring data, this is a good place to do it. And I could see some
uses for it myself.

Hobbit is intended to provide a good basis for your monitoring, but it
cannot solve everyones needs. If I can add a few lines of code that lets
users connect their own custom tools so they are fed by the data that
Hobbit collects, then there is a much better chance that they will stick
with Hobbit instead of picking some other tool.


So I added it, because it makes Hobbit much more flexible and allows
you to make more use of the data that Hobbit collects.


Regards,
Henrik