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https://issues.apache.org/jira/browse/AIRFLOW-2747?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ash Berlin-Taylor reopened AIRFLOW-2747:
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Some more work needed on this issue - the logs are wrong and the visibility in
the UI is now worse.
> Explicit re-schedule of sensors
> -------------------------------
>
> Key: AIRFLOW-2747
> URL: https://issues.apache.org/jira/browse/AIRFLOW-2747
> Project: Apache Airflow
> Issue Type: Improvement
> Components: core, operators
> Affects Versions: 1.9.0, 1.10.0
> Reporter: Stefan Seelmann
> Assignee: Stefan Seelmann
> Priority: Major
> Fix For: 2.0.0
>
> Attachments: Screenshot_2018-07-12_14-10-24.png,
> Screenshot_2018-09-16_20-09-28.png, Screenshot_2018-09-16_20-19-23.png,
> google_apis-23_r01.zip
>
>
> By default sensors block a worker and just sleep between pokes. This is very
> inefficient, especially when there are many long-running sensors.
> There is a hacky workaroud by setting a small timeout value and a high retry
> number. But that has drawbacks:
> * Errors raised by sensors are hidden and the sensor retries too often
> * The sensor is retried in a fixed time interval (with optional exponential
> backoff)
> * There are many attempts and many log files are generated
> I'd like to propose an explicit reschedule mechanism:
> * A new "reschedule" flag for sensors, if set to True it will raise an
> AirflowRescheduleException that causes a reschedule.
> * AirflowRescheduleException contains the (earliest) re-schedule date.
> * Reschedule requests are recorded in new `task_reschedule` table and
> visualized in the Gantt view.
> * A new TI dependency that checks if a sensor task is ready to be
> re-scheduled.
> Advantages:
> * This change is backward compatible. Existing sensors behave like before.
> But it's possible to set the "reschedule" flag.
> * The poke_interval, timeout, and soft_fail parameters are still respected
> and used to calculate the next schedule time.
> * Custom sensor implementations can even define the next sensible schedule
> date by raising AirflowRescheduleException themselves.
> * Existing TimeSensor and TimeDeltaSensor can also be changed to be
> rescheduled when the time is reached.
> * This mechanism can also be used by non-sensor operators (but then the new
> ReadyToRescheduleDep has to be added to deps or BaseOperator).
> Design decisions and caveats:
> * When handling AirflowRescheduleException the `try_number` is decremented.
> That means that subsequent runs use the same try number and write to the same
> log file.
> * Sensor TI dependency check now depends on `task_reschedule` table. However
> only the BaseSensorOperator includes the new ReadyToRescheduleDep for now.
> Open questions and TODOs:
> * Should a dedicated state `UP_FOR_RESCHEDULE` be used instead of setting
> the state back to `NONE`? This would require more changes in scheduler code
> and especially in the UI, but the state of a task would be more explicit and
> more transparent to the user.
> * Add example/test for a non-sensor operator
> * Document the new feature
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