[
https://issues.apache.org/jira/browse/AIRFLOW-1419?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16688014#comment-16688014
]
Conrad Lee commented on AIRFLOW-1419:
-------------------------------------
[~xnuinside] thanks for having a look. Also thanks for fining the bug in the
example code–I've fixed that.
I'm not sure this should be closed though. As I recall, before 1.8.2, no dummy
operator was required at all, because task-skip propagated differently. When
1.8.2 came along, all of a sudden a dummy was necessary – the question is
whether this is desired.
I much preferred this previous behavior–why should a dummy operator be
necessary at all? If one of the child tasks has a trigger rule thats stops the
propagation of task-skipping (such as ALL_DONE), then IMHO it should never be
skipped.
> Trigger Rule not respected downstream of BranchPythonOperator
> -------------------------------------------------------------
>
> Key: AIRFLOW-1419
> URL: https://issues.apache.org/jira/browse/AIRFLOW-1419
> Project: Apache Airflow
> Issue Type: Bug
> Affects Versions: 1.8.2
> Reporter: Conrad Lee
> Priority: Major
>
> Lets consider the following DAG:
> {noformat}
> ____________________
> / \
> branch_op confluence_op
> \______work_op________/
> {noformat}
> This is implemented in the following code:
> {code:java}
> import airflow
> from airflow.operators.python_operator import BranchPythonOperator
> from airflow.operators.dummy_operator import DummyOperator
> from airflow.utils.trigger_rule import TriggerRule
> from airflow.models import DAG
> args = {
> 'owner': 'airflow',
> 'start_date': airflow.utils.dates.days_ago(2)
> }
> dag = DAG(
> dag_id='branch_skip_problem',
> default_args=args,
> schedule_interval="@daily")
> branch_op = BranchPythonOperator(
> task_id='branch_op',
> python_callable=lambda: 'work_op',
> dag=dag)
> work_op = DummyOperator(task_id='work_op', dag=dag)
> confluence_op = DummyOperator(task_id='confluence_op', dag=dag,
> trigger_rule=TriggerRule.ALL_DONE)
> branch_op.set_downstream(confluence_op)
> branch_op.set_downstream(work_op)
> work_op.set_downstream(confluence_op)
> {code}
> Note that branch_op is a BranchPythonOperator, work_op and confluence_op are
> DummyOperators, and that confluence_op has its trigger_rule set to ALL_DONE.
> In dag runs where brancher_op chooses to activate work_op as its child,
> confluence_op never runs. This doesn't seem right, because confluence_op has
> two parents and a trigger_rule set that it'll run as soon as all of its
> parents are done (whether or not they are skipped).
> I know this example seems contrived and that in practice there are better
> ways of conditionally executing work_op. However, this is the minimal code to
> illustrate the problem. You can imagine that this problem might actually
> creep up in practice where originally there was a good reason to use the
> BranchPythonOperator, and then time passes and someone modifies one of the
> branches so that it doesn't really contain any children anymore, thus
> resembling the example.
--
This message was sent by Atlassian JIRA
(v7.6.3#76005)
