[rrd-users] rrdtool to provide persistence for service checks (Netsaint/Nagios..)

[Stanley Hopcroft]

Dear Ladies and Gentlemen,

I am writing about the use of rrdtool with availability monitors such as
Nocol/Snips, Netsaint/Nagios.

It seems to me that rrdtool is a natural choice when a service check
needs to keep state (to detect a change or a trend) because of the

. popularity of rrdtool
. wide range of language bindings
. simple standard interface


Not to mention the wonderful possibility of detecting anomalies (with
the HWPREDICT CF).

However, with Netsaint/Nagios at least, checks are scheduled by the
monitors scheduler according to 'check interval' and while this interval
may be exactly the same as the RRD step size, the check will rarely if
ever be executed on a step boundary (5 minutes past, 10 minutes past, 15
.. for a step size of 300).

This leads to rrdtool interpolating the values and this looks simply
ugly for GAUGE and ABSOLUTE data (while possibly making it a bit harder
to check for anomalies that integral values of ABSOLUTE may simplify).

Since it doesn't seem that interpolation can be suppressed, is there any
way of avoiding interpolated values ?

What failed to work for me was to 'round' the update time up to the
'nearest' step and use that in the update; a dump of the RRD showed that
the PDPs were all 0s !

($t  = time() ;
 $t += STEP_SIZE/2 ;
 $t -= $t % STEP_SIZE ;
 RRDs::update RRD, "$t:$v1:$v2..." ;
)

Thank you,

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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