# [rrd-users] Re: Creating RRD/RRA

Alex van den Bogaerdt alex at ergens.op.het.net
Thu May 12 02:53:39 MEST 2005

```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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