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https://issues.apache.org/jira/browse/AIRFLOW-2319?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16438020#comment-16438020
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Andreas Költringer commented on AIRFLOW-2319:
---------------------------------------------

I wanted to submit a PR so I started thinking how to resolve this. One way 
would be to just delete the one line referenced above. While this solves the 
issue for new setups, it would require all existing installations to manually 
adapt the database.

The other way I was thinking about was creating a migration, something like:
{code:java}
from alembic import op
import sqlalchemy as sa


def upgrade():
    op.drop_constraint('dag_id', 'dag_run', type_='unique')


def downgrade():
    pass{code}
I did not test it with "serious" databases like MariaDB, but this fails with 
SQLite.

So, any guidance on how to proceed? THX!

> Table "dag_run" has (bad) second index on (dag_id, execution_date)
> ------------------------------------------------------------------
>
>                 Key: AIRFLOW-2319
>                 URL: https://issues.apache.org/jira/browse/AIRFLOW-2319
>             Project: Apache Airflow
>          Issue Type: Bug
>          Components: DagRun
>    Affects Versions: 1.9.0
>            Reporter: Andreas Költringer
>            Priority: Major
>
> Inserting DagRun's via {{airflow.api.common.experimental.trigger_dag}} 
> (multiple rows with the same {{(dag_id, execution_date)}}) raised the 
> following error:
> {code:java}
> {models.py:1644} ERROR - No row was found for one(){code}
> This is weird as the {{session.add()}} and {{session.commit()}} is right 
> before {{run.refresh_from_db()}} in {{models.DAG.create_dagrun()}}.
> Manually inspecting the database revealed that there is an extra index with 
> {{unique}} constraint on the columns {{(dag_id, execution_date)}}:
> {code:java}
> sqlite> .schema dag_run
> CREATE TABLE dag_run (
>         id INTEGER NOT NULL, 
>         dag_id VARCHAR(250), 
>         execution_date DATETIME, 
>         state VARCHAR(50), 
>         run_id VARCHAR(250), 
>         external_trigger BOOLEAN, conf BLOB, end_date DATETIME, start_date 
> DATETIME, 
>         PRIMARY KEY (id), 
>         UNIQUE (dag_id, execution_date), 
>         UNIQUE (dag_id, run_id), 
>         CHECK (external_trigger IN (0, 1))
> );
> CREATE INDEX dag_id_state ON dag_run (dag_id, state);{code}
> (On SQLite its a unique constraint, on MariaDB its also an index)
> The {{DagRun}} class in {{models.py}} does not reflect this, however it is in 
> [migrations/versions/1b38cef5b76e_add_dagrun.py|https://github.com/apache/incubator-airflow/blob/master/airflow/migrations/versions/1b38cef5b76e_add_dagrun.py#L42]
> I looked for other migrations correting this, but could not find any. As this 
> is not reflected in the model, I guess this is a bug?



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