[rrd-developers] Re: daily PDP points misaligned in non-GMT timezones

Alex van den Bogaerdt alex at ergens.op.het.net
Fri Sep 2 09:58:17 MEST 2005

On Fri, Sep 02, 2005 at 05:25:02PM +1000, Peter Payne wrote:

> Because I started my rrdtool file at midnight, I expect my 24 hour
> segments (86,400 seconds) to run from midnight to midnight every day.
> But I am wrong.

Indeed, you are wrong.

> How can this be? It implies that the data points are running from 10AM
> to 10AM instead of midnight to midnight. Very suspicious!

Each interval will start and end at a whole multiple of, in this case,
86400 seconds.

> Whoops, looks like any attempt to have a PDP point that doesn't
> precisely align (or mod into) 1 Jan 1970 00:00 GMT is going to be
> warped.

Not an attempt.  It does so by design.

> Create a static value in the header called "pdp_offset". This is
> calculated when the file is created and assumes that the starting time
> is a PDP boundary, and that all PDPs will be aligned from that point
> onwards. It is the behaviour I would naturally expect, anyway.

So you're creating a file in Australia and you use data from the
branch offices in England and France. Which offset are you going to
use?  Your local time? Theirs? What about daylight saving?


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