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Subject [GitHub] matt-land opened a new pull request #4136: Fix for scheduler infinite loop when evaluating non-UTC DAGs after DST
Date Mon, 05 Nov 2018 23:01:56 GMT
matt-land opened a new pull request #4136: Fix for scheduler infinite loop when evaluating
non-UTC DAGs after DST
   …ing than their start state
   Make sure you have checked _all_ steps below.
   ### Jira
   - [ ] My PR addresses the following [Airflow-1710](
issues and references them in the PR title. For example, "\[AIRFLOW-1710\] My Airflow PR"
     - In case you are fixing a typo in the documentation you can prepend your commit with
\[AIRFLOW-XXX\], code changes always need a Jira issue.
   ### Description
   - [X ] Here are some details about my PR, including screenshots of any UI changes:
   This fixes the infinite loop in the AF jobs scheduler scanning a DAG with a start date
in Daylight Savings Time while evaluating a potential run date in Standard Time.
   The infinite loop Airflow gets trapped in is below:
   `while next_run_date <= last_run.execution_date:
       next_run_date = dag.following_schedule(next_run_date)`
   dag.following_schedule is not incrementing as expected. It instead starts to repeating
values that dag.following_schedule has already returned.
   This is caused by an interaction between a pendulum instance timezone having a DST offset
this is 'illegal' for the evaluated next run date.
   IE, If I call following_schedule with a dag.timezone that has a DST offset of -5, but on
the date being evaluated the value should be -6, the function stops incrementing and repeats
ranges of values.
   The fix is to simply drop the dst offset from dag.timezone.  dag.following_schedule will
then increment normally, it fixes the infinite loop.
   ### Tests
   - [X] My PR adds the following unit tests __OR__ does not need testing for this extremely
good reason:
   I need help with my PR
   ### Commits
   - [ ] My commits all reference Jira issues in their subject lines, and I have squashed
multiple commits if they address the same issue. In addition, my commits follow the guidelines
from "[How to write a good git commit message](":
     1. Subject is separated from body by a blank line
     1. Subject is limited to 50 characters (not including Jira issue reference)
     1. Subject does not end with a period
     1. Subject uses the imperative mood ("add", not "adding")
     1. Body wraps at 72 characters
     1. Body explains "what" and "why", not "how"
   ### Documentation
   - [ ] In case of new functionality, my PR adds documentation that describes how to use
     - When adding new operators/hooks/sensors, the autoclass documentation generation needs
to be added.
   ### Code Quality
   - [ ] Passes `flake8`

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