[rrd-users] Re: Problem with graph and x-grid

[Rainer Bawidamann]

In article <85ECD694981ED411A39B0006295069B00120A0BE at dassne02.darmstadt.dsh.de>,
	dehrentr at debis.com ("Ehrentraut, Diana") writes:
> 
> I atached the graph I get. As you can see, the 29th of october is marked
> twice. It was the day of the daylightsavingtime(?) change. 
> The strange thing about this is, that until the 31st of october I didn't
> have any problem with it, only in november.

It is indeed the daylightsaving change. When drawing the x-grid rrdtool
steps through the time by increasing the tm_hour field in the tm
structure. The time is initialized to 00:00:00. Now when rrdtool adds
one day to Oct 29 00:00:00 mktime(3) changes the day and hour value in
the tm structure to be 29 resp. 23 (i.e. Oct 30 00:00:00 with daylightsaving
set is Oct 29 23:00:00 without daylightsaving). I added debug output to
rrdtool which gives

find_next_time -> 972684000 / Sat Oct 28 00:00:00 2000
find_next_time -> 972770400 / Sun Oct 29 00:00:00 2000
find_next_time -> 972856800 / Sun Oct 29 23:00:00 2000
find_next_time -> 972943200 / Mon Oct 30 23:00:00 2000
find_next_time -> 973029600 / Tue Oct 31 23:00:00 2000

You can see the jump between line 2 and 3.

The question is now what would be the correct behaviour. 24 hours after
Oct 29 00:00:00 is Oct 29 23:00:00 and the graph shows the value for
this time/date. Maybe it should be rounded up to Oct 30 00:00:00.
Now what's the Right Behaviour?

>  <<...OLE_Obj...>> 

Nice Try ...

Rainer
-- 
Rainer.Bawidamann at rz.uni-ulm.de

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