Cheatsheet: Watermarks

Track progress and event-time completeness in streaming pipelines.

TimestampedValue()

returns: TimestampedValue

Purpose

Assigns event-time timestamps to elements before they enter temporal windows.

Syntax Signaturebeam.window.TimestampedValue(value, timestamp)

Usage Example

import apache_beam as beam

timestamped = records | "Add Timestamps" >> beam.Map(
    lambda x: beam.window.TimestampedValue(x, x["epoch_time"])
)

Used In

Reading elements from files or message fields lacking implicit timestamps.

Remember:

A Watermark is the runner's temporal completeness boundary; it guarantees that no elements with event-time t < T are expected.

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