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Re: Subversion and Daylight Savings Time

From: Mark Phippard <markphip_at_gmail.com>
Date: 2007-01-16 01:29:07 CET

On 1/15/07, Daniel Rall <dlr@collab.net> wrote:
>
> On Mon, 15 Jan 2007, Mark Phippard wrote:
>
> > On 1/15/07, Mark Phippard <markphip@gmail.com> wrote:
> > >
> > >On 1/15/07, Daniel Rall <dlr@collab.net> wrote:
> > >>
> > >> On Mon, 15 Jan 2007, Mark Phippard wrote:
> > >> ...
> > >> > We have been getting a lot of inquiries from our customers as to
> how
> > >> our
> > >> > products are impacted by the upcoming changes to DST. Most are
> > >> looking for
> > >> > official statements. It might save a lot of time and effort in the
> > >> long run
> > >> > if someone crafted a statement about Subversion and posted it to
> the
> > >> web
> > >> > site so that we could link to it when questions come to the mailing
> > >> lists.
> > >>
> > >> Good idea! Feel like writing one up? :)
> > >
> > >
> > >Sure. I'll at least look into it. I will probably try to keep it more
> > >general just saying that we get the date/time from the OS and use
> routines
> > >provided by the OS to transform it. The day of the year that DST
> changes
> > >is
> > >not relevant to these routines.
>
> Thanks Mark!
>
> > Index: dst-2007.html^M
> > ===================================================================^M
> > --- dst-2007.html (revision 0)^M
> > +++ dst-2007.html (revision 0)^M
> ...
> > +<h2 style="text-align: center">Statement of Support for 2007 Daylight
> > +Saving Time Changes</h2>
> > +
> > +<p>In August 2005 the US Congress passed the Energy Policy Act, which
> > +changes the dates of both the start and end of daylight saving time
> > +(DST). When this law goes into effect in 2007, DST will start three
> > +weeks earlier (2:00 A.M. on the second Sunday in March) and will
> > +end one week later (2:00 A.M. on the first Sunday in November)
> > +than what had traditionally occurred. This change was not adopted
>
> How about "universally adopted"?

Yes, that is better.

> +by all countries. For more information see: <a
> > +href="http://webexhibits.org/daylightsaving/b.html">
> > +http://webexhibits.org/daylightsaving/b.html</a></p>
> > +
> > +<p>These changes to DST do not require any special changes or fixes to
> > +the Subversion code. Subversion primarily uses dates/times to record
> > +when changes have been committed to the repository. This code runs
> > +on the server and gets the current date/time from the operating system
> > +and converts it to UTC using routines provided by the operating system.
>
> Yup, svn_time_to_cstring() produces a string which looks like:
>
> 2006-03-27T13:23:01.497707Z
>
> (IIRC, the Z is for "zulu", which is UTC/GMT.)
>
> > +The Subversion client receives these dates from the server and converts
> > +them to the local time zone for display using routines provided by
> > +the client operating system.
>
> Exactly happens to the date/time is going to be Subversion
> client-specific. While the conversion described above is quite true
> for the command-line binary (and a good way to go), it's possible that
> other clients (TortoiseSVN, Subclipse, etc.) might choose to display
> the time received from the server in some other fashion. Since this
> page is about both Subversion's libraries and client, we might want to
> indicate as much.

I figured it was not really necessary to mention the clients, because it
seems likely that they are just either showing the date/time in UTC or
converting it using whatever language-appropriate routine exists. In other
words, the answer would just be the same. It seems like other than
operating systems that automatically adjusts the date/time and maybe some
really time-sensitive scheduling apps, that hardly any apps would be
affected by this change. That being said, my company has been getting asked
this question an average of at least once a day in the last few weeks. I
think after Y2K, corporations are just in the mode of mass-sending these
sort of requests to their vendors.

> +1 to commit with tweaks.
>
> - Dan
>
>
>
I committed with just the one tweak. I assumed the code examples were just
confirming what I wrote (not suggestions for the doc).

http://subversion.tigris.org/dst-2007.html

-- 
Thanks
Mark Phippard
http://markphip.blogspot.com/
Received on Tue Jan 16 01:31:30 2007

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