Connection pooling in Flask - Mini Project: Build & Apply

Connection Pooling in Flask

📖 Scenario: You are building a simple Flask web app that connects to a database. To make your app faster and handle many users, you want to use connection pooling. Connection pooling means reusing database connections instead of opening a new one every time.

🎯 Goal: Build a Flask app that sets up a connection pool to a SQLite database and uses it to get data efficiently.

📋 What You'll Learn

Create a Flask app with a database connection pool

Use SQLAlchemy's connection pooling feature

Write a route that queries the database using the pool

Close connections properly after use

💡 Why This Matters

🌍 Real World

Connection pooling is used in web apps to improve performance by reusing database connections instead of opening new ones for every request.

💼 Career

Understanding connection pooling is important for backend developers to build scalable and efficient web applications.

1

Set up Flask app and database URL

Create a Flask app by importing Flask and initializing it as app. Also, create a variable called DATABASE_URL and set it to "sqlite:///example.db".

Flask

# Your code here

Need a hint?

Use Flask(__name__) to create the app. The database URL for SQLite starts with sqlite:///.

2

Configure SQLAlchemy engine with connection pool

Import create_engine from sqlalchemy. Create a variable called engine by calling create_engine with DATABASE_URL and set pool_size=5 and max_overflow=10 to configure the connection pool.

Flask

from flask import Flask

app = Flask(__name__)

DATABASE_URL = "sqlite:///example.db"
# Your code here

Need a hint?

Use create_engine with pool_size and max_overflow to set up pooling.

3

Write a route that queries the database using the pool

Create a Flask route for "/users" using @app.route. Inside the function get_users, use engine.connect() as conn in a with block. Execute the SQL query "SELECT name FROM users" using conn.execute() and fetch all results. Return the list of user names as a string joined by commas.

Flask

from flask import Flask
from sqlalchemy import create_engine

app = Flask(__name__)

DATABASE_URL = "sqlite:///example.db"

engine = create_engine(DATABASE_URL, pool_size=5, max_overflow=10)

# Your code here

Need a hint?

Use with engine.connect() as conn: to get a connection from the pool. Then run the query and collect names.

4

Add app run block for local testing

Add the standard Flask app run block: if __name__ == "__main__": and inside it call app.run(debug=True) to start the app in debug mode.

Flask

from flask import Flask
from sqlalchemy import create_engine

app = Flask(__name__)

DATABASE_URL = "sqlite:///example.db"

engine = create_engine(DATABASE_URL, pool_size=5, max_overflow=10)

@app.route("/users")
def get_users():
    with engine.connect() as conn:
        result = conn.execute("SELECT name FROM users")
        users = [row[0] for row in result]
    return ", ".join(users)

# Your code here

Need a hint?

This block lets you run the Flask app locally with debugging on.