implementing Thread Safety in a Flask Application Using SQLAlchemy 1.4 on Python 3.9
I'm reviewing some code and I'm maintaining legacy code that I'm relatively new to this, so bear with me... I'm working with a question with thread safety in my Flask application that uses SQLAlchemy 1.4 on Python 3.9. I'm running a multi-threaded server using Flask's built-in development server. When multiple requests are processed simultaneously, I receive a `sqlalchemy.exc.OperationalError` stating "(sqlite3.OperationalError) database is locked". I've tried using a session per request approach and ensuring that sessions are closed after each request, but the behavior continues. Here's how I configured my SQLAlchemy session in the Flask app: ```python from flask import Flask, request from flask_sqlalchemy import SQLAlchemy app = Flask(__name__) app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///test.db' app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False db = SQLAlchemy(app) class User(db.Model): id = db.Column(db.Integer, primary_key=True) username = db.Column(db.String(80), unique=True, nullable=False) @app.route('/add_user', methods=['POST']) def add_user(): user_data = request.json new_user = User(username=user_data['username']) db.session.add(new_user) db.session.commit() return {'message': 'User added'}, 201 if __name__ == '__main__': app.run(threaded=True) ``` I'm currently using the Flask built-in server for simplicity during development, but I suspect that the SQLite backend is causing locking issues under concurrent access. I have also tried setting the `check_same_thread` parameter to `False` in the SQLite URI, but that hasn't resolved the scenario. Do you have any recommendations on how to handle this question? Should I switch to a different database engine like PostgreSQL for better concurrency support, or is there a way to configure SQLite for better performance in a multi-threaded environment? What am I doing wrong? This issue appeared after updating to Python 3.11. Any suggestions would be helpful. What's the correct way to implement this?