Скачать или смотреть Solving SQLite Database Locking in Django/Celery with Concurrent Access

Learn how to manage SQLite database locks in Django 5.1 and Celery 5.4 setups by reducing transaction duration and optimizing concurrency.
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The Problem: SQLite Database Locked During Concurrent Access

Using SQLite with Django and Celery is common for local or small-scale projects. However, even with recommended "production-ready" settings, you might encounter the dreaded database is locked OperationalError when performing concurrent writes or long-running transactions.

Context

Django 5.1 project with SQLite as the database.

Celery 5.4 used for background task processing.

Tasks run serially in the Celery worker.

Tasks perform operations inside a with transaction.atomic() block, including querying the database, calling external APIs, and updating the database again.

SQLite is configured with WAL mode, busy timeout, immediate transaction mode, and other performance PRAGMAs.

Despite these, concurrent writes fail with a lock.



Why Does SQLite Lock Occur?

SQLite allows multiple readers but only one writer at a time. Write operations acquire exclusive locks,
which block other writes and sometimes reads when the lock lasts too long.

Key points:

Long transactions (especially those involving external API calls) hold exclusive locks longer.

WAL mode improves concurrency but doesn't eliminate potential write conflicts if transactions overlap.

transaction_mode='IMMEDIATE' causes the transaction to reserve the database immediately, blocking concurrent writers early.



Practical Solution: Minimize Transaction Duration

Key Strategy:

Do not hold open database transactions while waiting for external IO like API calls.

Why?

Extended transactions lock the database, preventing other writes.

Even with WAL and busy timeouts, SQLite can't queue competing writes indefinitely.

How to Implement:

Break your task logic into distinct steps.

Perform database queries and updates in atomic transactions only around those operations.

Call external APIs outside of any transaction blocks.

For example:

[[See Video to Reveal this Text or Code Snippet]]

This approach reduces lock duration, letting other writes queue or proceed.



Additional Recommendations

Use SQLite only for development or low-concurrency scenarios. For production-level concurrency, consider PostgreSQL or MySQL.

Configure Celery concurrency wisely, especially if tasks access the same database.

Keep transactions as short as possible.

Use select_for_update() judiciously to explicitly lock rows only when necessary.



Summary

Even with sophisticated SQLite pragmas and Django 5.1's new transaction_mode settings, SQLite's locking still depends on the duration of database transactions. The best way to avoid database locked errors in Django + Celery setups is to:

Keep transactions short.

Never surround external API calls inside transactions.

Design your task flow to separate database I/O and external I/O explicitly.

These simple practices unlock smoother concurrency and more reliable background processing with SQLite.