[rrd-users] Re: Creating RRD/RRA

[Sorrell, Al]

Another way is simply to feed the time in such a way as to guarantee
that it's an exact multiple of the step on the step; i.e., if step is
3600, guarantee that the time fed into the RRD is an exact multiple of
3600 (modulo 3600). Obviously, this assumes that you cron it to run on
the hour and that a second or two is not a major factro in the data. At
least that seems to work for me, 
Al
-----Original Message-----
From: rrd-users-bounce at list.ee.ethz.ch
[mailto:rrd-users-bounce at list.ee.ethz.ch] On Behalf Of Alex van den
Bogaerdt
Sent: Wednesday, May 11, 2005 8:54 PM
To: rrd-users at list.ee.ethz.ch
Subject: [rrd-users] Re: Creating RRD/RRA

On Wed, May 11, 2005 at 06:34:05PM -0400, Mike M wrote:
> > ... let's say the following is true:
> > 
> > now == around 12:00 METDST today == 1115805601 seconds since epoch
> > now == around 13:00 METDST today == 1115809202 seconds since epoch
> > now == around 14:00 METDST today == 1115812800 seconds since epoch
> > now == around 15:00 METDST today == 1115816401 seconds since epoch
> > 
> > Assume step == 3600 and heartbeat == 3600.  What do you think
> > happens at time 1115809202 (_around_ 13:00) ?  And at 1115816401 ?
> > And why?
> > 
> > What do you think if heartbeat is set to 3300 ?  Why ?
> 
> I see what you're getting at here, although given the question I think
> using the socratic method is a little much.  A simple answer would do
> just fine, not that I don't appreciate the help.

It is the "around" part that is going to cause trouble for you.

> > now == around 12:00 METDST today == 1115805601 seconds since epoch
> > now == around 13:00 METDST today == 1115809202 seconds since epoch

1115809202 - 1115805601 = 3601 > 3600 => rate = NaN

also

1115809202 - 1115805601 = 3601 > 3300 => rate = NaN

In general: delta(time) should be <= heartbeat


You need to give yourself some space, or you need to get your
times fixed (i.e. on the hour _exactly_).  I can't tell you what
to do, this depends on your requirements.

Please do show the list what your next try is, so we can feedback again.

cheers
Alex

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