SQLite Database Locking and Concurrency Errors After Cursor Build
Your Cursor-generated application uses SQLite as its database and works fine during development with a single user, but fails with SQLITE_BUSY or "database is locked" errors as soon as multiple users access it simultaneously. Write operations timeout, reads sometimes return stale data, and the app becomes unreliable under any real load.
Cursor frequently chooses SQLite because it's the simplest database to set up — no server to configure, just a file. But SQLite's concurrency model is fundamentally different from PostgreSQL or MySQL. It uses file-level locking, meaning only one write can happen at a time, and readers can block writers depending on the journal mode.
This issue typically surfaces immediately after deploying to production or during load testing when more than a handful of concurrent users interact with the application.
Error Messages You Might See
Common Causes
- Default journal mode (DELETE) — SQLite's default journal mode allows only one writer at a time and blocks all readers during writes
- Multiple connections without WAL mode — Each request opens a new connection but WAL (Write-Ahead Logging) mode isn't enabled, causing lock contention
- Long-running transactions — Cursor generated code that holds database locks during slow operations (API calls, file processing) within a transaction
- Concurrent writes from multiple processes — Serverless or multi-process deployments create multiple processes all trying to write to the same SQLite file
- No busy timeout configured — The default busy timeout is 0ms, meaning any lock contention immediately throws an error instead of retrying
How to Fix It
- Enable WAL mode — Run
PRAGMA journal_mode=WAL;on your database connection. WAL allows concurrent readers and a single writer, dramatically improving performance - Set a busy timeout — Configure
PRAGMA busy_timeout=5000;to wait up to 5 seconds for locks instead of immediately failing - Use a single connection with serialization — For web apps, use a connection pool of size 1 with a write queue, or use better-sqlite3 (synchronous) instead of sqlite3 (async) in Node.js
- Keep transactions short — Never do network calls, file I/O, or heavy computation inside a database transaction. Read data, release the lock, process, then write back
- Consider migrating to PostgreSQL — If your app needs real concurrent access, SQLite may not be the right choice. Use PostgreSQL or MySQL with a connection pool
- Move SQLite to a persistent volume — If staying with SQLite, ensure the database file is on a persistent volume, not ephemeral serverless storage
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Get HelpFrequently Asked Questions
Can SQLite handle a production web application?
SQLite can handle low-to-medium traffic apps (up to a few hundred concurrent users) if configured correctly with WAL mode, busy timeouts, and proper connection management. For high-traffic apps or serverless deployments, PostgreSQL is a better choice.
What is WAL mode and why does it help?
Write-Ahead Logging (WAL) mode changes how SQLite handles concurrent access. Instead of locking the entire database for writes, it writes changes to a separate WAL file. This allows readers to continue reading the old data while a write is in progress, dramatically reducing lock contention.