Problems / Caching, medium
5 million products, 2 KB each, but the cache has 512 MB. Popular items fit; most don’t.
Free to open. Runs in your browser, no sign-up.
Success ≥ 99%, p99 ≤ 300 ms.
3,000 requests a second for 30 seconds: 90% reads, 10% writes.
What each component does in this design, and what calls it. The simulator mimics each one from these settings.
| Component | Its job here | Settings |
|---|---|---|
| Load balancerLoad balancer | Traffic enters here.Calls API.Layer 4 balancers route by IP and port; layer 7 balancers read HTTP and can route by path or header. | – |
| APIApp service | Load balancer forwards to it.Calls Redis cache (checked first), Postgres.Little's law: throughput ≈ concurrency ÷ latency. 200 slots at 50 ms serve about 4,000 req/s. | 3 replicas × 200 slots · timeout 1.0 s |
| Redis cacheCache | API checks it first for reads.An in-memory cache like Redis usually answers in well under a millisecond inside one region. | 512 MB memory |
| PostgresSQL database | API reads it when Redis cache misses. API calls it for writes.Postgres runs one process per connection, which is why poolers like PgBouncer sit in front of busy databases. | 2 vCPU · 40 connections |
Try it first. Open one hint at a time if you get stuck.
Look at the cache’s hit rate and memory.
Working set vs memory decides the hit rate.
Give the cache more memory (“set the cache memory to 8 GB”).