rdblue commented on pull request #1355:
URL: https://github.com/apache/iceberg/pull/1355#issuecomment-675604146


   @zhangdove, Iceberg does not modify timestamps other than converting between 
representations (like micros to millis).
   
   Timestamp modification or adjustment to display a value by time zone is done 
by processing engines, not by Iceberg itself. Iceberg must only store values 
and return the same values.
   
   Timestamp values are in microseconds and come in two flavors: timestamp is a 
zoneless date and time represented as microseconds from the Unix epoch in UTC, 
and timestamptz is an instant in time represented as microseconds from the Unix 
epoch in UTC.
   
   The report in #1354 uses Spark. Spark only supports timestamptz and it 
passes values to Iceberg as microseconds from epoch, which Iceberg returns to 
Spark unmodified. The `day` partition function is not specific to a zone, which 
is probably the source of the confusion. The daily boundaries used by that 
function are UTC day boundaries, if I remember correctly.


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