3. Data & Persistence
Transactions, Concurrency & Idempotency
Prevent duplicate writes and inconsistent state when requests, workers and retries happen concurrently.
Lesson overview
Transactions provide atomicity, but concurrency still requires explicit reasoning. Idempotency keys, unique constraints and appropriate isolation prevent retries and simultaneous requests from creating invalid state.
Learning path
Theory → Example → Code → Practice → Quiz → Challenge → Completion
Step 1
Theory
Transactions provide atomicity, but concurrency still requires explicit reasoning. Idempotency keys, unique constraints and appropriate isolation prevent retries and simultaneous requests from creating invalid state.
Step 2
Example
A webhook delivered three times should record its event ID once and safely return the previous result on later deliveries.
Step 3
Code
sql
insert into processed_events(event_id)
values ('evt_123')
on conflict (event_id) do nothing;
Step 4
Practice
Review your current application and apply Transactions, Concurrency & Idempotency. Document the current behavior, one production risk, the change you would make, and how you would verify it.
Step 5
Quiz
1. What is the central production concern in "Transactions, Concurrency & Idempotency"?
Step 6
Challenge
Design a production-ready implementation for Transactions, Concurrency & Idempotency. Include failure handling, security considerations, observability, testing and a rollback or recovery path where applicable.
Complete every stage
Work through every step in order, then the lesson will be marked complete.
Each chapter and subtopic has its own public URL under /full-stack-to-production.