Connection pooling in FastAPI - Performance & Optimization

Performance: Connection pooling

HIGH IMPACT

Connection pooling affects how quickly the server can handle database requests by reusing open connections instead of opening new ones each time.

Managing database connections efficiently in FastAPI

FastAPI

from asyncpg import create_pool

pool = await create_pool(dsn)

async def get_data():
    async with pool.acquire() as conn:
        result = await conn.fetch('SELECT * FROM table')
    return result

Reuses existing connections from the pool, avoiding repeated connection setup costs.

📈 Performance GainReduces request latency by 50-200ms, improves INP and server throughput

Managing database connections efficiently in FastAPI

FastAPI

async def get_data():
    conn = await asyncpg.connect(dsn)
    result = await conn.fetch('SELECT * FROM table')
    await conn.close()
    return result

Opening and closing a new database connection for every request adds significant latency and CPU overhead.

📉 Performance CostBlocks request handling for 50-200ms per connection setup, increasing INP and reducing throughput

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
No connection pooling (new connection per request)	N/A	N/A	N/A	[X] Bad
Using connection pooling with asyncpg in FastAPI	N/A	N/A	N/A	[OK] Good

Rendering Pipeline

Connection pooling reduces backend wait times for database responses, speeding up the server's response generation before sending HTML or JSON to the browser.

→Server Processing

→Network Response

⚠️ BottleneckDatabase connection setup time

Core Web Vital Affected

INP

Connection pooling affects how quickly the server can handle database requests by reusing open connections instead of opening new ones each time.

Optimization Tips

1Always use connection pooling to reuse database connections in FastAPI.

2Avoid opening and closing connections per request to reduce latency.

3Monitor backend response times to verify pooling effectiveness.

Performance Quiz - 3 Questions

What is the main performance benefit of using connection pooling in FastAPI?

A Blocks rendering until all connections close

B Reduces latency by reusing open database connections

C Increases the number of database connections opened

D Improves CSS selector performance

DevTools: Network

How to check: Open DevTools Network panel, observe time to first byte (TTFB) for API calls to backend endpoints.

What to look for: Lower TTFB indicates faster backend response, showing effective connection pooling.