Manually Terminating Blocking Queries
If it's not desirable to automatically terminate queries, you can configure django-pgmigrate to show the blocking queries so that they can be manually handled.
Set settings.PGMIGRATE_BLOCKING_ACTION to pgmigrate.Show to configure this behavior. For example, in settings.py:
Here's an example of what it looks like:
In the above, a warning message is printed when blocking activities are found. The Postgres process IDs of the activities are printed. Queries will remain blocked until they finish or are manually terminated.
Manually Inspecting and Terminating Queries
django-pgmigrate automatically installs the django-pgactivity library, which makes it easy to view and terminate active queries.
Our original example printed a blocking ID of 38076. We can run the following to show the duration of the query and the SQL:
python manage.py pgactivity 38076
Output looks like this:
38076 | 0:00:36 | IDLE_IN_TRANSACTION | None | select * from auth_user;
The second column is the duration of the query. The final column is the SQL. You can terminate the query with:
python manage.py pgactivity 38076 --terminate
Once the query is terminated, migrations will continue.
Tip
The pgactivity command can take multiple process IDs. These can be directly copied from the output of the pgmigrate command.
Adding Application Context to Queries
The django-pgactivity library comes with middleware to automatically annotate the URL that issued the SQL statement, adding more information to help you understand where queries originate. Add pgactivity.middleware.ActivityMiddleware to settings.MIDDLEWARE, and python manage.py pgactivity will also show the application context in the results.
Once configured, our example output from above would look like this:
38076 | 0:00:36 | IDLE_IN_TRANSACTION | {'url': '/admin/', 'method': 'GET'} | select * from auth_user;
We recommend reading the django-pgactivity docs to learn more about how it works, along with learning how to add context to management commands and background tasks. The docs also explain how to configure the pgactivity command for other use cases.