[rrd-users] Re: RRD setup when collection only daily

[Alex van den Bogaerdt]

Serge Maandag wrote:

> If he sets his step to 86400 and his ds heartbeat to:
> 86400 + (a small interval in case he runs late with his daily update)
> And he does his first update at midnight, wouldn't that just be what he
> wants?
> His pdp's would be at 00:00 exactly.

No, unless you work in UTC time.  All times inside RRDtool are a
whole multiple of the step size.  If the step size is 86400, today
would be 1019174400.  This is 1019250638 - (1019250638 % 86400).
Perl shows the time: perl -e 'use POSIX;print ctime(1019174400)'
which results in 'Fri Apr 19 02:00:00 2002' (local time).

> I can see why your method works, but wonder what the advantage is.

If the step size is 3600, the current time minus the modulo would be
perl -e 'use POSIX;print ctime(1019250638 - (1019250638 % 3600));'
Fri Apr 19 23:00:00 2002

So, if I would update now, in the first example I would update at
02:00 local time, in the second example I would update at 23:00
local time.  Similarly, if I would update just after midnight I
would still update at 02:00 (the day before!) in the first example
while I would update at 00:00 (*that* day) in the second example.

> b.t.w., on the rrdtool site under the heartbeat and the step it says:
> 
> ``heartbeat'' is not only the maximum acceptable interval between
> samples, but also the maximum acceptable amount of ``unknown'' time per
> PDP (obviously this is only significant if you have ``heartbeat'' less
> than ``step'').
> 
> Is this right? I believe that the x-files factor for the ds is the
> parameter that determines this.

xff is for the amount of PDPs per CDP.

cheers,
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