Different filesystem types also have different time granularity – eg FAT32 and
NTFS, one way this manifests is as if a utility such as XCOPY /U to copy later
files from one volume type to another, and if the same command is repeated the
same files may be copied again, because the timestamps are slightly different.
FAT - 2 seconds
exFAT - 10 milliseconds
NTFS - 100 nanoseconds
Changes in DST are processed differently also depending on whether the PC has
been rebooted since the last DST time change
To give a hint at the complexity - more info from
https://msdn.microsoft.com/en-us/library/windows/desktop/ms724290(v=vs.85).aspx
A file time is a 64-bit value that represents the number of 100-nanosecond
intervals that have elapsed since 12:00 A.M. January 1, 1601 Coordinated
Universal Time (UTC). The system records file times when applications create,
access, and write to files.
The NTFS file system stores time values in UTC format, so they are not affected
by changes in time zone or daylight saving time. The FAT file system stores
time values based on the local time of the computer. For example, a file that
is saved at 3:00pm PST in Washington is seen as 6:00pm EST in New York on an
NTFS volume, but it is seen as 3:00pm EST in New York on a FAT volume.
Time stamps are updated at various times and for various reasons. The only
guarantee about a file time stamp is that the file time is correctly reflected
when the handle that makes the change is closed.
Not all file systems can record creation and last access times, and not all
file systems record them in the same manner. For example, the resolution of
create time on FAT is 10 milliseconds, while write time has a resolution of 2
seconds and access time has a resolution of 1 day, so it is really the access
date. The NTFS file system delays updates to the last access time for a file by
up to 1 hour after the last access.
From: Ross Levis
Sent: Friday, November 25, 2016 12:57 PM
To: 'NZ Borland Developers Group - Delphi List'
Subject: Re: [DUG] Timezones for Bills and things
Yep, so some devices are showing daylight savings time and others are not for
the same physical file, proving the file is stored in UTC and being displayed
in local time.
From: [email protected]
[mailto:[email protected]] On Behalf Of Rohit Gupta
Sent: Friday, 25 November 2016 10:48 a.m.
To: NZ Borland Developers Group - Delphi List
Subject: Re: [DUG] Timezones for Bills and things
Not quite. Because I am not referring to the actual timestamp that it is
showing me. But the fact that between the 5pcs, a laptop and surface and usb
harddisk. The timestamps are different twice a year. If it was storing them
as utc then they would all be always in sync with each other. They would all
change by the same hour and look the same in beyond compare. But different
files change their timestamps on different pcs. If its storing them as utc
then it is selective about it. Which is worse than not saving them as utc.
Rohit
On 25/11/2016 10:06, David Brennan wrote:
Hi,
Surely that is evidence that Windows is storing timestamps in UTC? If it
wasn’t then a file stamped as 3pm would always say 3pm no matter what timezone
you changed your computer to.
Regards,
David.
From: [email protected]
[mailto:[email protected]] On Behalf Of Rohit Gupta
Sent: Friday, 25 November 2016 9:59 a.m.
To: NZ Borland Developers Group - Delphi List
mailto:[email protected]
Subject: Re: [DUG] Timezones for Bills and things
Thanks Ross,
however I would dispute that windows stores file timestamps in utc. Because
twice a year there is mayhem as only some files change their timestamp by an
hour. And these files are different on different workstations.
Maybe it's true for the server version of windows.
Rohit
On 24/11/2016 17:39, Ross Levis wrote:
I suggest store in UTC, like Windows does for file timestamps, and use
Windows functions like GetTimeZoneInformation and
SystemTimeToTzSpecificLocalTime to convert to locale time for display/printing
purposes. A timezone database shouldn’t be required.
From: [email protected]
[mailto:[email protected]] On Behalf Of Stefan Mueller
Sent: Thursday, 24 November 2016 5:21 p.m.
To: 'NZ Borland Developers Group - Delphi List'
Subject: Re: [DUG] Timezones for Bills and things
https://github.com/pavkam/tzdb has such a timezone database (2014 data).
Using that library makes it easy to convert between timezones.
I think http://www.iana.org/time-zones hosts the latest up to date time
zone data that this tzdb database is based on in case you want to update it to
the latest 2016 data.
Or you could rewrite your application to use Oracle Database … they do have
a timestamp datatype for your table columns so when you select/insert/update a
table all you need to do is to set the correct locale and the database will do
the conversion for you.
https://docs.oracle.com/database/121/NLSPG/ch4datetime.htm#NLSPG263
Kind regards,
Stefan Müller,
R&D Manager
ORCL Toolbox Ltd.
Auckland, New Zealand
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This message is intended for the adresse named above and may contain
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From: [email protected]
[mailto:[email protected]] On Behalf Of Rohit Gupta
Sent: Thursday, 24 November 2016 4:19 p.m.
To: NZ Borland Developers Group - Delphi List
Subject: [DUG] Timezones for Bills and things
We finally have to deal with time zones. We use the server date-time
everywhere, rather than relying on workstation date-times. This is not an
interactive forum type application where the flow of data is merged from
various timezones. It is a business management system with appointments and
bills etc. The timestamps of these records have to remain as created. But
they can not come from the workstation clock.
Going forward, a database server could be servicing workstations in
different time zones.
I am considering
1.. Set the server time as UTC
2.. Keep a table for time zone versus branch (how do I keep this upto
date at daylight saving boundaries)
3.. Use the utc + timezone difference to stamp each bill or appointment
made for each branch.
How is everyone else handling it ?
Regards
Rohit
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Regards
Rohit Gupta
B.E. Elec., M.E., Mem IEEE, Mem IET
Technical Director
Computer Fanatics Ltd
Tel 4892280
Fax 4892290
Web www.cfl.co.nz
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Technical Director
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Fax 4892290
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