Unexpected problem: DirsSync-1.3-rc3 - directories synchronizer

Discussion in 'Python' started by GerritM, Nov 1, 2003.

  1. GerritM

    GerritM Guest

    I downloaded and tried the recently announced dirsync program. It looks
    nice, but...

    I have two presumably identical directories: one at home and one at work. I
    keep them synchronized by means of zipping changed files and extracting them
    at the other side. When comparing both directories by means of this nice
    program I discovered that all files differ, with an mtime difference of
    exactly 1 hour. I am working on a windows 98 machine at home, Windows 2000
    at work. Winzip 8.0. Somewhere in the chain a time coversion takes place,
    errorneously...

    Most suspect for me is the fileserver at work, since I try to compare a
    recent snapshot made at work with my directory at home. Careful examination
    of a zipfile created before the wintertime started and a zipfile created
    after this date shows a one hour difference for files before the critical
    date.All zipfiles were made at work (windows 2000, data residing on a
    fileserver; make unknown, presumably on Linux/Unix).

    Anyone seen comparable problems? This effect is rather disastrous if you use
    timestamps for synchronization :-(

    regards Gerrit

    --
    www.extra.research.philips.com/natlab/sysarch/
     
    GerritM, Nov 1, 2003
    #1
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  2. On Sat, 1 Nov 2003 21:39:47 +0100, rumours say that "GerritM"
    <> might have written:

    >I downloaded and tried the recently announced dirsync program. It looks
    >nice, but...
    >
    >I have two presumably identical directories: one at home and one at work. I
    >keep them synchronized by means of zipping changed files and extracting them
    >at the other side. When comparing both directories by means of this nice
    >program I discovered that all files differ, with an mtime difference of
    >exactly 1 hour. I am working on a windows 98 machine at home, Windows 2000
    >at work. Winzip 8.0. Somewhere in the chain a time coversion takes place,
    >errorneously...
    >
    >Most suspect for me is the fileserver at work, since I try to compare a
    >recent snapshot made at work with my directory at home. Careful examination
    >of a zipfile created before the wintertime started and a zipfile created
    >after this date shows a one hour difference for files before the critical
    >date.All zipfiles were made at work (windows 2000, data residing on a
    >fileserver; make unknown, presumably on Linux/Unix).
    >
    >Anyone seen comparable problems? This effect is rather disastrous if you use
    >timestamps for synchronization :-(
    >
    >regards Gerrit


    I presume you also live in a Daylight Savings Time timezone?

    Yes, welcome to the beautiful world of Windows timestamps... windows
    system calls that return file timestamps do not take into account that a
    file changed during summer time had +1 hour difference from UTC compared
    to a file changed after the end of summer time, and they assume constant
    time difference throughout the year. If you don't believe me, change
    the date/time to a little before time changes in your location, create a
    file, check its timestamp, wait a little till the time changes, then
    check its timestamp again.

    I believe POSIX compatibility did not specifically include honesty in
    the requirements for the return values of system calls... or even
    cluefulness on behalf of the POSIX-compatible-OS-wannabe-developers.

    The only thing I could do in my own directory sync code (mind you, using
    sets.Set helps a lot in finding differences!) was to optionally add 1
    hour to the returned timestamp if the timestamp falls between last
    Sunday of March, 03:00 localtime and last Sunday of October, 03:00
    localtime. I also carefully avoid to touch files in the involved
    computer when the time is between one hour minus and one hour plus the
    time-change times for various precautionary reasons :)

    How many times can I use the word time in a sentence?
    --
    TZOTZIOY, I speak England very best,
    Ils sont fous ces Redmontains! --Harddix
     
    Christos TZOTZIOY Georgiou, Nov 4, 2003
    #2
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