The Connection Pool Starvation

PagerDuty — checkout 503s with healthy DB CPU

SRE Team: /api/checkout returning 503. DB CPU 10% — pool 50/50 maxed. Requests timing out waiting for connections.

The trap: DB connection held for the entire checkout including the 2s Stripe call. 50 users = pool exhausted.

Your task

Fix `process_checkout()` in `checkout_service.py`: release the connection before stripe.charge_card(), re-acquire only to save the receipt.

Book: wrap logic in one transaction · Prod: scope transactions to DB ops only.