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Notes / Docker Sandboxes / CQRS Architecture & Read Model Projections
Docker Sandboxes · Tier 4: Architect & Chaos · Lab 55

CQRS Architecture & Read Model Projections

Separate write commands from read queries with Command Query Responsibility Segregation (CQRS). Master why monolithic multi-table SQL joins exhaust database connection pools, stream append-only domain events from PostgreSQL, project denormalized JSON read views into Redis with sub-millisecond O(1) latency, guard against out-of-order event replay with monotonic version checks, and rebuild read stores from scratch.

Time30 minutes
StackPostgreSQL 16Ports 15485, 16410
MemoryAbout 180 MB
Before thisLab 41Transactional Outbox Pattern & Pol
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Verified runWindows, Mac, LinuxBash and PowerShell
  1. 1PrepareWhat you will learn
  2. 2PredictGuess before you run
  3. 3RunStep by step
  4. 4ObserveWhat you should see
  5. 5Break itChange one thing
  6. 6Clean upLeave nothing running
On this page
  1. 00 / What You Will Learn
  2. 01 / Why It Matters
  3. 02 / What We Are Building
  4. 03 / Words You Need
  5. 04 / Predict First
  6. 05 / Step by Step
  7. 06 / What You Should See
  8. 07 / Look Inside
  9. 08 / Break It, Fix It
  10. 09 / In Real Projects
  11. 10 / Interview Corner
  12. 11 / Clean Up

00 /What You Will Learn

By the end you will be able to
  • Understand why normalized 3NF schemas excel for write commands but choke under high-frequency read dashboards.
  • Reproduce the negative control: monolithic 4-table SQL joins degrading latency and locking database resources.
  • Implement atomic domain mutations alongside domain event emission using the Transactional Outbox pattern.
  • Build an asynchronous projection engine transforming event streams into denormalized Redis read models.
  • Benchmark sub-millisecond O(1) read latency offloading 100% of analytical read traffic from the write OLTP database.
  • Implement monotonic version guards to safely discard delayed or out-of-order event projections.
  • Rebuild corrupted read caches from scratch by replaying the immutable event log.

Before you start

Finish Lab 41 (Transactional Outbox Pattern) and Lab 54 (PostgreSQL CDC Logical Decoding) first. You should understand how transactional event logs prevent dual-write bugs and how asynchronous workers tail database changes. Docker Desktop must be running.