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

[Alex van den Bogaerdt]

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.

> POSSIBLE SOLUTION
> 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?

Alex

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