learning/katas/python/Streaming/Triggers/Early Triggers/task.md

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Early Triggers
--------------

Triggers allow Beam to emit early results, before all the data in a given window has arrived. For
example, emitting after a certain amount of time elapses, or after a certain number of elements
arrives.

**Kata:** Given that sample events generated with one second granularity and a fixed window of 1-day duration,
please implement an early trigger that emits the number of events count immediately after new
element is processed.

<div class="hint">
  Use <a href="https://beam.apache.org/releases/pydoc/current/apache_beam.transforms.trigger.html#apache_beam.transforms.trigger.AfterWatermark">
  the early parameter</a> to set early firing triggers.
</div>

<div class="hint">
  Use <a href="https://beam.apache.org/releases/pydoc/current/apache_beam.transforms.window.html#apache_beam.transforms.window.FixedWindows">
  FixedWindows</a> with 1-day duration using
  <a href="https://beam.apache.org/releases/pydoc/current/apache_beam.transforms.trigger.html#apache_beam.transforms.trigger.AfterWatermark">
  AfterWatermark</a> trigger.
</div>

<div class="hint">
  Set the <a href="https://beam.apache.org/releases/pydoc/current/apache_beam.transforms.core.html?highlight=allowed_lateness#apache_beam.transforms.core.Windowing">
  allowed lateness</a> to 0 with
  <a href="https://beam.apache.org/releases/pydoc/current/apache_beam.transforms.trigger.html#apache_beam.transforms.trigger.AccumulationMode">
    discarding accumulation mode</a>.
</div>

<div class="hint">
  Use <a href="https://beam.apache.org/releases/pydoc/current/apache_beam.transforms.core.html#apache_beam.transforms.core.CombineGlobally">
  CombineGlobally</a> and
  <code>CountCombineFn</code> to calculate the count of events.
</div>

<div class="hint">
  Refer to the Beam Programming Guide
  <a href="https://beam.apache.org/documentation/programming-guide/#event-time-triggers">
    "Event time triggers"</a> section for more information.
</div>