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  1. Qt
  2. QTBUG-120285

QDateTime::fromString() takes much longer time in Qt6.6 than in Qt5.15

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    • Windows

    Description

      Reproducer attached.

      A performance issue with QDateTime::fromString.

      The customer reported :
       - The function has slowed down drastically between Qt 5.15.x (the previous Qt release the customer used) and Qt 6.6.0.
       - this issue was monitored only with Windows.
       - based on the customer's profiling, it seems that most of the time is spent in QWinTimeZonePrivate::availableWindowsIds function.
       - Running the code on the customer's laptop takes ~100ms with Qt 5.15 and ~10000ms with Qt 6.6.

       

      The same issue was reproduced at my laptop as well, the result was as follows:

        Qt 6.6.1:
          XXX - 10000 x QDateTime::fromString took 4965 milliseconds

        Qt 5.15.16
          XXX - 10000 x QDateTime::fromString took 49 milliseconds

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            Eddy Edward Welbourne
            hitoshiito Hitoshi Ito
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            Dates

              Created:
              Updated:
              Resolved: