django-pgmigrate helps you avoid costly downtime with Postgres migrations.
Imagine the following happens:
- A long-running task queries a model in a transaction and keeps the transaction open.
python manage.py migratetries to change a field on the model.
Because of how Postgres queues locks, this common scenario causes every subsequent query on the model to block until the query from 1) has finished.
django-pgmigrate provides the following features to alleviate problematic locking scenarios when running migrations:
- Detect blocking queries and terminate them automatically (the default behavior).
- Print blocking queries so that you can inspect and terminate them manually.
- Set the lock timeout so that migrations are terminated if they block too long.
Install django-pgmigrate with:
pip3 install django-pgmigrate
After this, add pgactivity, pglock, and pgmigrate to the INSTALLED_APPS setting of your Django project.
After following the installation instructions, running python manage.py migrate will automatically terminate any blocking queries. Here's an example of what it looks like:
There are two additional outputs in the migrate command versus the original:
- The first output line shows the Postgres process ID. This is useful for querying activity that's blocking the process.
- The yellow text shows when a blocking query was detected and terminated. In our case, it was blocking auth migration 12.
You can configure django-pgmigrate to show blocked queries instead of automatically killing them, and you can also set the lock timeout to automatically cancel migrations if they block for too long. See the documentation section below for more details.
django-pgmigrate is compatible with Python 3.9 - 3.13, Django 4.2 - 5.1, Psycopg 2 - 3, and Postgres 13 - 17.
View the django-pgmigrate docs here to learn more about:
- How blocking queries are automatically terminated.
- Configuring the command to show blocking activity instead of terminating it, along with instructions on how to manually view and terminate activity.
- Configuring lock timeouts to automatically stop migrations if they block for too long.
- Advanced usage such as creating custom actions to run when queries are blocked.
For information on setting up django-pgmigrate for development and contributing changes, view CONTRIBUTING.md.