![]() Moving application servers from one time zone to another will lead to a wrong interpretation of already stored timestamps.A value written by server A and read by server B will be different from the same value written by server B and read by server A. If application servers sharing the same database belong to different time zones, there will be a huge mess in time offsets.NET when reading columns of time-zone-unaware types. While reading from the database, a date/time object can be created without a time zone - for example, DateTime in.The time zone offset may be ignored at deserialization, especially in custom serializers.The serialization mechanism may use a format that doesn’t include the time zone offset.Time on the client may be created without a time zone - for example, DateTime in.If it is GMT -5, the value displayed to the second user must be October 3, 2022, 08:13:36.Įverything looks consistent, but let’s see what can go wrong in this flow. The client deserializes the received timestamp into a date/time object converting its value to the local time zone.The value is converted to a string representation and sent to the client - “2022–10–03T 14:13:36+01:00”.Since the server works in GMT +1, the value will be treated as a timestamp in this time zone. The server reads the value from the database and creates a date/time object holding October 3, 2022, 14:13:36.In our example October 3, 2022, 14:13:36 will be persisted with no information about the time zone. Let’s assume the database doesn’t store a time zone for date/time values. The server stores the timestamp in the database.If the server runs in GMT +1, the object will contain October 3, 2022, 14:13:36. The server deserializes the timestamp into a date/time object converting its value to the local time zone.The value is converted to a string representation and sent to the server - “2022–10–03T 15:13:36+02:00”.To better understand how we can reliably implement this behavior, let’s look at a sample data flow when a timestamp is set by a user and then goes through all layers in both directions. We must ensure that our system works this way and shows timestamps according to the client’s time zone. There is a question - what time should the central office see? Obviously, the software in the central office must show 1:26:43 PM for the specimen (minus an hour) because this event happened at this exact moment in their time zone. The timestamp mentioned in the example above was logged by the laboratory. Let’s imagine the laboratory that collected the specimen is in the +2 time zone, while its central office, which tracks how medical tests are performed, is in +1. Those who don’t have time and desire to read through all the details can skip to the summary right away. Let’s review each case one by one considering general recommendations as well. ![]() Schedule - “a data import from the legacy system must occur every weekday at 8 AM”.Time span - “it took 3 minutes and 12 seconds to export the catalog”. ![]()
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