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https://issues.apache.org/jira/browse/AIRFLOW-214?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15317063#comment-15317063
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Bolke de Bruin commented on AIRFLOW-214:
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The PR works, that is for sure. I do not understand why the task can get
detached in the first place. Session should be consistent and it happens right
after dagrun.get_task_instances. It does not happen every time but I could
replicate it with example_skip_dag, but couldnt fix it by keeping the current
session.
> TaskInstance can get detached in process_dag
> --------------------------------------------
>
> Key: AIRFLOW-214
> URL: https://issues.apache.org/jira/browse/AIRFLOW-214
> Project: Apache Airflow
> Issue Type: Bug
> Components: scheduler
> Reporter: Bolke de Bruin
> Fix For: Airflow 1.8
>
>
> Is some rare occasions the TaskInstance can get detached in process_dag. It
> is unclear why
> {code}[2016-06-06 17:47:37,048] {models.py:3444} INFO - Updating state for
> <DagRun example_skip_dag @ 2016-06-05 00:00:00:
> scheduled__2016-06-05T00:00:00, externally triggered: False> considering 8
> task(s)
> [2016-06-06 17:47:37,059] {jobs.py:670} ERROR - Instance <TaskInstance at
> 0x10d3e9410> is not bound to a Session; attribute refresh operation cannot
> proceed
> Traceback (most recent call last):
> File
> "/Users/bolke/Documents/dev/airflow_env/lib/python2.7/site-packages/airflow-1.7.1.2-py2.7.egg/airflow/jobs.py",
> line 667, in _do_dags
> self.process_dag(dag, tis_out)
> File
> "/Users/bolke/Documents/dev/airflow_env/lib/python2.7/site-packages/airflow-1.7.1.2-py2.7.egg/airflow/jobs.py",
> line 531, in process_dag
> task = dag.get_task(ti.task_id)
> File
> "/Users/bolke/Documents/dev/airflow_env/lib/python2.7/site-packages/sqlalchemy/orm/attributes.py",
> line 237, in __get__
> return self.impl.get(instance_state(instance), dict_)
> File
> "/Users/bolke/Documents/dev/airflow_env/lib/python2.7/site-packages/sqlalchemy/orm/attributes.py",
> line 578, in get
> value = state._load_expired(state, passive)
> File
> "/Users/bolke/Documents/dev/airflow_env/lib/python2.7/site-packages/sqlalchemy/orm/state.py",
> line 474, in _load_expired
> self.manager.deferred_scalar_loader(self, toload)
> File
> "/Users/bolke/Documents/dev/airflow_env/lib/python2.7/site-packages/sqlalchemy/orm/loading.py",
> line 610, in load_scalar_attributes
> (state_str(state)))
> DetachedInstanceError: Instance <TaskInstance at 0x10d3e9410> is not bound to
> a Session; attribute refresh operation cannot proceed{code}
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