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Re: [hobbit] Client interval question


Well, we could take this the other way, and say that we only wanted to
run our tests once every 10 minutes, because it was causing too much
overhead to run the tests every 5 minutes. How would we deal with that?


Same issue, the server needs to know the sampling rate when the RRD is created.

I think there are benefits, on the client side, the client should pass
the frequency which it is calling the tests at, to them, so that for
example, the vmstat test can adjust how long it will run for to either
600 seconds, or 60 seconds, or whatever else is needed.

As long as those never need to change, that wouldn't be too bad. But then you run into the display logic needing help depending on the granularity of the data/RRAs in the RRDs.


Further to that, there is some additional work (which I feel is the real
place that all the work is involved, the client side stuff would be
quite simple, or so it sounds).

Yes.
So, the question becomes, how difficult is it to convert an rrd file,
which was initially created to store data-points every 300 seconds, such
that we can now store data-points every X seconds?

I am not aware of a way to change the granularity of RRAs (the things inside the RRDs) once they are created. You'd have to rrdtool export; create a new rrd with different RRA's, then rrdtool import. Basically export/import the database. You can't even add an RRA to an existing RRD.

The second part to this question, is how does hobbit know how frequently
you want to send your reports? ie, it can't be based on 'however often
they are received', because that value would change very frequantly, ie,
the reports are done every 300 seconds, but by the time the report is
submitted/processed by hobbit, it might be 1 or 2 seconds late/early
compared to last time..... Could hobbit server 'learn' the frequency
from the client (which is where this is configured anyway), because the
client would report that value to the server as a part of the vmstat
output?

Yes, but that is not what makes all this really hard, it's the server logic. I can think of ways to do it, but it would involve a lot of changes to the server side parsing, many small client changes, restructuring/redefining existing rrds, and some potentially hairy presentation logic to make the server smarter about what to show based on what is in the RRD. I wrote larrd with Christian, and I can tell you, this would not be a weekend hack.

Time Series Data (telemetry data) is all about data on regular intervals. Changing that regular interval is a very significant thing.

or anything else, I have no interest in any of it, I'm just stating a
simple fact of life (you want something done, you can't do it, so find
someone who can do it, and motivate them to the point where they will do
it whether they want to or not)...

The real trick there is convincing them they want to do it. Forcing someone to do something might work, but is no good over the long term. 

Agreed, it would be nice to not have to run hobbit plus something else
when they are both collecting the same data (just a different
frequency).


I'm tellin' ya: vmstat 5

scott