Re: Discuss regarding Ticket 263

----- Original Message ----- 
From: "Jean-Edouard Babin" <[email protected]>
To: "Alex van den Bogaerdt" <[email protected]>
Cc: <[email protected]>
Sent: Monday, May 24, 2010 7:19 PM
Subject: Re: [rrd-developers] Discuss regarding Ticket 263



> Yes, conditional (G)PRINT would be better, but rrdtool set a "false"
> default time to the VDEF result anyway.

> > Using 0 was a design choice.

This is not a false timestamp, it is overloaded so to speak, 0 means false, 
unset.

> > I don't think time 0 will ever be valid, so instead of adding something 
> > to
> > this struct, why not simply if (vdef->when==0) printf("none"); else
> > {...whatever is done now...}

> Imagine someone doing statistic and importing data from 1970 to 2010,
> with one value per month and the fewest one on 1st Jan 1970.

I did back then, read on

> If he wants to print the first value and use a VDEF for that, he would
> not get it's result even if in his case 0 is the correct value.
> From my point of view adding 'never' flag is better as it can't break 
> something

Does RRDtool actually work properly when working with timestamps around 
1970?

When I programmed the (basics of) VDEF, it didn't.  If memory serves me 
well, it has been a while, so maybe the next changed, 1980-01-01 or so was 
the earliest date one could use (or reliably use).

What timestamp results from local time 1970-01-01 00:00 ?  It will result in 
0 for the UK, Iceland, and other places where during the winter there's no 
time difference with UTC. In a large part of Europe it will be 3600. In 
timezones west of Greenwich (UK) it will have to be a negative value.  Does 
that actually work? West of Greenwich includes the Americas, not really a 
small part of the world.

Bottom line:
If things have changed, perhaps 0 is no longer a suitable false value. But 
chances are it is as valid as it has been, so then use it.

HTH
Alex