[rrd-developers] Daylight saving time change issue with rrdtool fetch

Hermann Lauer Hermann.Lauer at iwr.uni-heidelberg.de
Sat Apr 5 22:39:23 CEST 2008


during daylight change last year I got a fault in a python application
with the rrdtool module returning a false error.
This can be easily demonstrated with the
commandline tool, too (tested under linux with 1.2.15, 1.2.23 and 1.3beta4):

$ export TZ=Europe/Berlin
$ rrdtool fetch sample.rrd -s 1193533140 -e 1193533200 AVERAGE
ERROR: start (1193536740) should be less than end (1193533200)
$ unset TZ
$ rrdtool fetch sample.rrd -s 1193533140 -e 1193533200 AVERAGE
<normal output suppressed>

After looking at the code in parsetime() in src/parsetime.c to me it looks like 
rrdtools time parser makes an for unix seconds superfluos double
conversion where that dst issue most probably originates from.

To circumvent the error someone could be tempted to use relative
times, but then the 
data returned is probably wrong.

Hope this helps cleaning up that issue - or are I'm somehow wrong ?


Netzwerkadministration/Zentrale Dienste, Interdiziplinaeres 
Zentrum fuer wissenschaftliches Rechnen der Universitaet Heidelberg
IWR; INF 368; 69120 Heidelberg; Tel: (06221)54-8236 Fax: -5224
Email: Hermann.Lauer at iwr.uni-heidelberg.de

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