django-pgtransaction 2.1.0

A context manager/decorator which extends Django's atomic function with the ability to set isolation level and retries for a given transaction.

django-pgtransaction

django-pgtransaction offers a drop-in replacement for the default django.db.transaction module which, when used on top of a PostgreSQL database, extends the functionality of that module with Postgres-specific features.

At present, django-pgtransaction offers an extension of the django.db.transaction.atomic context manager/decorator which allows one to dynamically set transaction characteristics including:

• Isolation level
• Read mode (READ WRITE/READ ONLY)
• Deferrability (DEFERRABLE/NOT DEFERRABLE)
• Retry policy for Postgres locking exceptions

See the quickstart below or the docs for examples.

Quickstart

After installation, set transaction characteristics using pgtransaction.atomic:

Isolation Levels

Set the isolation level for specific consistency guarantees:

import pgtransaction

with pgtransaction.atomic(isolation_level=pgtransaction.SERIALIZABLE):
    # Do queries with SERIALIZABLE isolation...

There are three isolation levels: pgtransaction.READ_COMMITTED, pgtransaction.REPEATABLE_READ, and pgtransaction.SERIALIZABLE. By default it inherits the parent isolation level, which is Django's default of "READ COMMITTED".

Read-Only Transactions

Read-only mode can be used queries that don't modify data:

with pgtransaction.atomic(read_mode=pgtransaction.READ_ONLY):
    # Can only read, not write
    results = MyModel.objects.all()

Deferrable Transactions

Prevent serialization failures for long-running queries by blocking:

with pgtransaction.atomic(
    isolation_level=pgtransaction.SERIALIZABLE,
    read_mode=pgtransaction.READ_ONLY,
    deferrable=pgtransaction.DEFERRABLE
):
    # Long-running read-only query that won't cause serialization conflicts
    analytics_data = expensive_query()

Note: DEFERRABLE only works with SERIALIZABLE isolation level and READ_ONLY mode.

Retries for Concurrent Updates

When using stricter isolation levels like pgtransaction.SERIALIZABLE, Postgres will throw serialization errors upon concurrent updates to rows. Use the retry argument with the decorator to retry these failures:

@pgtransaction.atomic(isolation_level=pgtransaction.SERIALIZABLE, retry=3)
def do_queries():
    # Do queries...

Note that the retry argument will not work when used as a context manager. A RuntimeError will be thrown.

By default, retries are only performed when psycopg.errors.SerializationError or psycopg.errors.DeadlockDetected errors are raised. Configure retried psycopg errors with settings.PGTRANSACTION_RETRY_EXCEPTIONS. You can set a default retry amount with settings.PGTRANSACTION_RETRY.

Nested Usage

pgtransaction.atomic can be nested, but keep the following in mind:

1. Isolation mode cannot be changed once a query has been performed.
2. Read-write mode can not be changed to from within a read only block.
3. The retry argument only works on the outermost invocation as a decorator, otherwise RuntimeError is raised.

Compatibility

django-pgtransaction is compatible with Python 3.10 - 3.14, Django 4.2 - 6.0, Psycopg 2 - 3, and Postgres 14 - 18.

Documentation

Check out the Postgres docs to learn about transaction isolation in Postgres.

View the django-pgtransaction docs here

Installation

Install django-pgtransaction with:

pip3 install django-pgtransaction

After this, add pgtransaction to the INSTALLED_APPS setting of your Django project.

Contributing Guide

For information on setting up django-pgtransaction for development and contributing changes, view CONTRIBUTING.md.

Creators

• Paul Gilmartin
• Wes Kendall