Neil Hanlon created AIRFLOW-246:
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Summary: 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
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:
[pre]
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;
[/pre]
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