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https://issues.apache.org/jira/browse/AIRFLOW-246?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15356998#comment-15356998
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Matthias Huschle commented on AIRFLOW-246:
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Do I understand the query correctly, that it delivers different results than
before, as it double counts the TI belonging to the last DAG run if it is still
running? Not that I'd consider this a bad trade-off, but it might be worth
noting it.
> dag_stats endpoint has a terrible query
> ---------------------------------------
>
> Key: AIRFLOW-246
> URL: https://issues.apache.org/jira/browse/AIRFLOW-246
> Project: Apache Airflow
> Issue Type: Bug
> Components: webserver
> Affects Versions: Airflow 1.7.1
> Environment: MySQL Backend through sqlalchemy
> Reporter: Neil Hanlon
> Assignee: Kengo Seki
>
> Hitting this endpoint creates a series of queries on the database which take
> over 20 seconds to run, causing the page to not load for that entire time.
> Luckily the main page (which includes this under "Recent Statuses") loads
> this synchronously, but still... waiting almost half a minute (at times more)
> to see the statuses for dags is really not fun.
> We have less than a million rows in the task_instance table--so it's not even
> a problem with that.
> Here's a query profile for the query:
> https://gist.github.com/NeilHanlon/613f12724e802bc51c23fca7d46d28bf
> We've done some optimizations on the database, but to no avail.
> The query:
> {code:sql}
> SELECT task_instance.dag_id AS task_instance_dag_id, task_instance.state AS
> task_instance_state, count(task_instance.task_id) AS count_1 FROM
> task_instance LEFT OUTER JOIN (SELECT dag_run.dag_id AS dag_id,
> dag_run.execution_date AS execution_date FROM dag_run WHERE dag_run.state =
> 'running') AS running_dag_run ON running_dag_run.dag_id =
> task_instance.dag_id AND running_dag_run.execution_date =
> task_instance.execution_date LEFT OUTER JOIN (SELECT dag_run.dag_id AS
> dag_id, max(dag_run.execution_date) AS execution_date FROM dag_run GROUP BY
> dag_run.dag_id) AS last_dag_run ON last_dag_run.dag_id = task_instance.dag_id
> AND last_dag_run.execution_date = task_instance.execution_date WHERE
> task_instance.task_id IN ... AND (running_dag_run.dag_id IS NOT NULL OR
> last_dag_run.dag_id IS NOT NULL) GROUP BY task_instance.dag_id,
> task_instance.state;
> {code}
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