Using RRDs to get persistence (state retention) for service checks not possible.

Dear Ladies and Gentlemen,

I am writing to say that I think it is not possible to use an RRD to 
store the (time series) results of a service check as a means of 
providing persistence for stateful checks.

(Examples of such checks might be determining that nett rates are below 
threshold or that current rates for non counter type processes are 
within threshold: determining that a slow running process is actually 
alive).

RRDs rely on being updated with check results at regular periodic 
intervals.

Netsaint on the other hand schedules checks depending upon what's 
happening and to ensure that checks are executed in a timely manner.

If the RRD is not updated when it expects to be the data value is 
interpolated so that the values fetched from the RRD are suprising and 
probably not helpful.

It seems to me that RRDs are best updated by another process - not by a 
Netsaint check - and that Netsaint checks can read RRDs and check time 
series data that is updated by something else (MRTG, Cricket etc).

Yours sincerely. 



-- 
------------------------------------------------------------------------
Stanley Hopcroft
------------------------------------------------------------------------

'...No man is an island, entire of itself; every man is a piece of the
continent, a part of the main. If a clod be washed away by the sea,
Europe is the less, as well as if a promontory were, as well as if a
manor of thy friend's or of thine own were. Any man's death diminishes
me, because I am involved in mankind; and therefore never send to know
for whom the bell tolls; it tolls for thee...'

from Meditation 17, J Donne.


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