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https://issues.apache.org/jira/browse/AIRFLOW-6974?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17089938#comment-17089938
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Sam T commented on AIRFLOW-6974:
--------------------------------

Hi [~RosterInn], not a perfect solution. I verified you can delete the 
example_subdag_operator.py, the initdb will work. I verified with the following 
SQL server.

Microsoft SQL Server 2017 (RTM-CU13) (KB4466404) - 14.0.3048.4 (X64) 

Microsoft SQL Server 2017 (RTM-CU13) (KB4466404) - 14.0.3048.4 (X64)  Nov 30 
2018 12:57:58  Copyright (C) 2017

Microsoft Corporation Developer Edition (64-bit) on Linux (Ubuntu 16.04.5 LTS)
h2. Remove:
h2. 
[airflow|https://github.com/apache/airflow/tree/v1-10-stable]/[airflow|https://github.com/apache/airflow/tree/v1-10-stable/airflow]/[example_dags|https://github.com/apache/airflow/tree/v1-10-stable/airflow/example_dags]/*example_subdag_operator.py*

> Using MS SQL Server 17 as a backend, Migration 
> cc1e65623dc7_add_max_tries_column_to_task_instance.py fails if load_examples 
> = True
> ----------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: AIRFLOW-6974
>                 URL: https://issues.apache.org/jira/browse/AIRFLOW-6974
>             Project: Apache Airflow
>          Issue Type: Bug
>          Components: database
>    Affects Versions: 1.10.9
>            Reporter: Tony Brookes
>            Priority: Minor
>         Attachments: airflow-mssql-stack-trace.txt, 
> image-2020-04-20-18-14-10-275.png
>
>
> This took me a while to figure out as there was another issue with the 
> migration in question which is 
> cc1e65623dc7_add_max_tries_column_to_task_instance.py
> This file USED to have an issue where it would sit there forever during an 
> initdb on MS SQL Server, essentially deadlocked with itself.
> I couldn't figure out why it was still sitting there for me, given that I was 
> using the version of the migration where this had been fixed, so I went 
> looking at the locks on the DB.  I found TWO processes running on the DB both 
> originating inside the airflow initdb Python instance.
> The first was happily sitting there trying to query the max_retries column on 
> a table, but the other was attempting to query the table "slot_pool" from 
> within example_subdag_operator.py .  I killed the session which was querying 
> that table and of course my Python process crashed, helpfully with a stack 
> trace.
> The session I killed was interacting with the DB running in EXAMPLES and was 
> actually complaining that the table was not a valid object name.  As soon as 
> I set load_examples = False, the initdb process ran through in a few seconds 
> and all was well.  But with load_examples = True it would reliably hang on 
> this specific migration every single time.
> I have attached a full stack trace from when I terminated the second DB 
> session.



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