Re: Telling if a given datetime is within the DST switchover

------------ Original Message ------------ > Date: Monday, March 30, 2015 20:04:56 +0100 > From: Lester Caine <lester@lsces.co.uk> > > On 30/03/15 16:41, Larry Martell wrote: >>>> The use case is that I have a server uptime reporting script >>>> and it >>>> >> uses a database of times that the server was able to be >>>> >> pinged. If there is no entry for a period it indicated the >>>> >> server was down. So on March 29, running in London, it found >>>> >> no entries from 1am to 2am and it reported the server was >>>> >> down for an hour, when in fact the period from 1am to 2am >>>> >> did not exist because of the switch to summer time. >>> > >>> > If you are logging ANYTHING other than UTC then your reporting >>> > system is the problem. You DISPLAY times using the local time, >>> > and log everything using a clean UTC time. >> I 100% agree with you, but this client does not do that. I have >> told them they should, but they did not want to change. > > As Ryan says ... convert to UTC to do the check, but personally > I'd be looking at why 1amGMT and 2amBST is reporting 2 hours > rather than 1 hour. I've been through this many years ago now with > clients who simply recorded the 'time'. Railway timetables never > used to run over night at that time, but when they started, > timetables got interesting ;) When the underlying process was > switched to UTC and all of the hacks to get the correct running > times were removed the objections were also removed. > > I presume that all you get from the database is '1am' or '2am', so > you just need to add the missing offset information from the > calendar. So you have 1amGMT and 2amBST to compare. > You can get the information you're after with "zdump -v" of the zoneinfo file for a timezone, e.g., zdump -v GB | grep 2015 GB Sun Mar 29 00:59:59 2015 UTC = Sun Mar 29 00:59:59 2015 GMT isdst=0 gmtoff=0 GB Sun Mar 29 01:00:00 2015 UTC = Sun Mar 29 02:00:00 2015 BST isdst=1 gmtoff=3600 GB Sun Oct 25 00:59:59 2015 UTC = Sun Oct 25 01:59:59 2015 BST isdst=1 gmtoff=3600 GB Sun Oct 25 01:00:00 2015 UTC = Sun Oct 25 01:00:00 2015 GMT isdst=0 gmtoff=0 how you deal with it from there is up to you -- there are many options I would think, including loading it into a DB that you check. The system TZ files do change from time to time, as the local rules change, so you'd need to manage for that. - Richard