Clean up the Airflow metadata database using DAGs

In addition to storing configurations about your Airflow environment, the Airflow metadata database stores data about past and present task runs. Airflow never automatically removes metadata, so the longer you use it, the more task run data is stored in your metadata DB. Over a long enough time, this can result in a bloated metadata DB, which can affect performance across your Airflow environment.

When a table in the metadata DB is larger than 50GB, you might start to experience degraded scheduler performance. This can result in:

• Slow task scheduling
• Slow DAG parsing
• Gunicorn timing out when using the Celery executor
• Slower Airflow UI load times

The following tables in the database are at risk of becoming too large over time:

• dag_run
• job
• log
• rendered_task_instance_fields
• task_instance
• xcom

To keep your Airflow environment running at optimal performance, you can clean the metadata DB using the Airflow CLI airflow db clean command. This command was created as a way to safely clean up your metadata DB without querying it directly. This tutorial describes how to implement a cleanup DAG in Airflow so that you can clean your database using the command directly from the Airflow UI.

danger

Even when using airflow db clean, deleting data from the metadata database can destroy important data. Read the Warnings section carefully before implementing this tutorial DAG in any production Airflow environment.

Warnings

Deleting data from the metadata database can be an extremely destructive action. If you delete data that future task runs depend on, it's difficult to restore the database to its previous state without interrupting your data pipelines. Before implementing the DAG in this tutorial, consider the following:

• When specifying the clean_before_timestamp value, use as old a date as possible. The older the deleted data, the less likely it is to affect your currently running DAGs.
• On Astro, the DAG fails if it runs for longer than five minutes, which can happen if a table has an exceptionally large amount of data to delete. If this happens, use the DAG's params to reduce the amount of data deleted from a single table at once by moving the clean_before_timestamp to a less recent time.

Prerequisites

• An Airflow project project
• The Astro CLI

Step 1: Create your DAG

warning

This DAG has been designed and optimized for Airflow environments running on Astro. Consider adjusting the parameters and code if you're running the DAG in any other type of Airflow environment.

1. In your dags folder, create a file called db_cleanup.py.

2. Copy the following code into the file.

   """A DB Cleanup DAG maintained by Astronomer. Note that there is a global database statement timeout of 5 minutes, so if you have large tables you want to clean, you may need to run the cleanup in smaller batches."""
   
   from datetime import UTC, datetime, timedelta
   
   from airflow.cli.commands.db_command import all_tables
   from airflow.decorators import dag
   from airflow.models.param import Param
   from airflow.operators.bash import BashOperator
   
   
   @dag(
       dag_id="astronomer_db_cleanup_dag",
       schedule_interval=None,
       start_date=datetime(2024, 1, 1),
       catchup=False,
       is_paused_upon_creation=False,
       description=__doc__,
       doc_md=__doc__,
       tags=["cleanup"],
       params={
           "clean_before_timestamp": Param(
               default=datetime.now(tz=UTC) - timedelta(days=90),
               type="string",
               format="date-time",
               description="Delete records older than this timestamp. Default is 90 days ago.",
           ),
           "tables": Param(
               default=[],
               type=["null", "array"],
               examples=all_tables,
               description="List of tables to clean. Default is all tables.",
           ),
           "dry_run": Param(
               default=False,
               type="boolean",
               description="Print the SQL queries that would be run, but do not execute them. Default is False.",
           ),
       },
   )
   def astronomer_db_cleanup_dag():
       BashOperator(
           task_id="clean_db",
           bash_command="""\
               airflow db clean \
                --clean-before-timestamp {{ params.clean_before_timestamp }} \
           {% if params.dry_run -%}
                --dry-run \
           {% endif -%}
                --skip-archive \
           {% if params.tables -%}
                --tables {{ params.tables|join(', ') }} \
           {% endif -%}
                --verbose \
                --yes \
           """,
           do_xcom_push=False,
       )
   
   
   astronomer_db_cleanup_dag()

   Rather than running on a schedule, this DAG is triggered manually by default and includes params so that you're in full control over how you clean the metadata DB.

   It includes one task, clean_db, that runs airflow db clean with the params you specify at runtime. The params let you specify:

   • What age of data to delete. Any data that was created before the specified time will be deleted. The default is to delete all data older than 90 days.
   • Whether to run the cleanup as a dry run, meaning that no data is deleted. The DAG will instead return the SQL that would be executed based on other parameters you have specified. The default is to run the deletion without a dry run.
   • Which tables to delete data from. The default is all tables.

Step 2: Run the DAG

In this step, run the DAG in a local Airflow environment to practice the workflow for cleaning metadata DB data. When completing this process in a production environment, you would complete this process only after your Airflow environment has been running for a while.

1. Run astro dev start in your Astro project to start Airflow, then open the Airflow UI at localhost:8080.

2. In the Airflow UI, run the db_cleanup DAG by clicking the play button, then click Trigger DAG w/ Config. Configure the following params:

   • dry_run: true
   • tables: all_tables
   • clean_before_timestamp: datetime.now(tz=UTC) - timedelta(days=90)

3. Click Trigger.

4. After the task completes, click Graph.

5. Click a task run.

6. Click Instance Details.

7. Click Log.

8. Check that the airflow db cleanup command completed successfully. Note that if you created a new Astro project for this tutorial, the run will not show much data to be deleted.

You can now use this DAG to periodically clean data from the Airflow metadata DB as needed.