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From "Jeremiah Lowin (JIRA)" <>
Subject [jira] [Assigned] (AIRFLOW-62) XCom push not working reliably
Date Fri, 06 May 2016 20:42:13 GMT


Jeremiah Lowin reassigned AIRFLOW-62:

    Assignee: Jeremiah Lowin

> XCom push not working reliably
> ------------------------------
>                 Key: AIRFLOW-62
>                 URL:
>             Project: Apache Airflow
>          Issue Type: Bug
>          Components: db, operators
>    Affects Versions: Airflow 1.7.0
>         Environment: Postgres backed Airflow running with Celery inside of the puckel
Docker setup.
>            Reporter: Alex Papanicolaou
>            Assignee: Jeremiah Lowin
> I have a DAG that polls for activity in various data streams from a database and then
uploads the activity statuses to a table.  Each of the polling tasks are python operators
that once they get the polling result, return a dict as an XCom push.  The dict contains two
entries which are strings, one which is a bool, and one which is a datetime object.  There
is a final task that pulls all the results and uploads the collective statuses to a table.
 I chose this pattern since I figured it might be better to do one collective write operation
on all the results.
> Before I moved ahead to the github master branch I was using 1.7.0 from PyPI and this
worked fine.  Now that I am on the github master branch, I find that the XCom pushing is unreliable.
 The returned values in the logs show up correctly but when doing the XCom pull, I get None
for some of the returned values.  Investigating the XCom result in the Webserver also shows
nothing there.  But if I rerun a task where the XCom failed, the push works and the XCom result
is as it should be.
> Nothing appears to have changed in the codebase so I am at a loss.  Perhaps it really
wasn't working before?  How would the backing postgres handle these simultaneous writes? 
I can't imagine that would be a problem.

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