uranusjr commented on a change in pull request #17552: URL: https://github.com/apache/airflow/pull/17552#discussion_r689287086
########## File path: docs/apache-airflow/dag-run.rst ########## @@ -54,17 +54,31 @@ Cron Presets Your DAG will be instantiated for each schedule along with a corresponding DAG Run entry in the database backend. -.. note:: +Data Interval +------------- + +Each DAG run in Airflow has an assigned "data interval" that represents the time +range it operates in. For a DAG scheduled with ``@daily``, for example, each of +its data interval would start at midnight of each day, and end at midnight of +the next day. + +A DAG run happens *after* its associated data interval has ended, to ensure the +run is able to collect all the actual data within the time period. Therefore, a +run covering the data period of 2020-01-01 will not start to run until +2020-01-01 has ended, i.e. 2020-01-02 onwards. + +All dates in Airflow are tied to the data interval concept in some way. The +"logical date" (also called ``execution_date`` from previous Airflow version) +of a DAG run, for example, usually denotes the start of the data interval, not +when the DAG is actually executed. Similarly, since the ``start_date`` argument +for the DAG and its tasks points to the same logical date, a run will only +be created after that data interval ends. So a DAG with ``@daily`` schedule and +``start_date`` of 2020-01-01, for example, will not be created until 2020-01-02. Review comment: I decided to remove this example since it is too similar to the one in the previous paragraph and could be more confusing than clarifying. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: commits-unsubscr...@airflow.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org