Assigns timestamps to all the elements of a collection.
In the following examples, we create a pipeline with a
PCollection and attach a timestamp value to each of its elements.
When windowing and late data play an important role in streaming pipelines, timestamps are especially useful.
Example 1: Timestamp by event time
The elements themselves often already contain a timestamp field.
beam.window.TimestampedValue takes a value and a
in the form of seconds.
Example 2: Timestamp by logical clock
If each element has a chronological number, these numbers can be used as a logical clock. These numbers have to be converted to a “seconds” equivalent, which can be especially important depending on your windowing and late data rules.
Example 3: Timestamp by processing time
If the elements do not have any time data available, you can also use the current processing time for each element. Note that this grabs the local time of the worker that is processing each element. Workers might have time deltas, so using this method is not a reliable way to do precise ordering.
By using processing time, there is no way of knowing if data is arriving late because the timestamp is attached when the element enters into the pipeline.
- Reify converts between explicit and implicit forms of Beam values.
Last updated on 2023/12/03
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