Problems / RAG and retrieval, medium

Semantic cache too strict

A semantic cache in front of a RAG assistant hits 10%: its similarity threshold is 0.99. The model quota can’t take the rest.

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Your goals

Success ≥ 99%, time to first token p99 ≤ 2.5 s.

Test cases

Like a coding problem, a solution has to pass every case, not just the one it was built for. Submit in the lab runs all 4; 1 of them are hidden until then.

  1. As given. The problem’s own traffic, scheduled failures and seed.
  2. A slow dependency. The main data store or model answers twice as slowly for part of the run.
  3. A server dies. One replica of the service with the most replicas is killed for part of the run.

The traffic

50 requests a second for 30 seconds: 100% request (reads).

The system

What each component does in this design, and what calls it. The simulator mimics each one from these settings.

ComponentIts job hereSettings
Load balancerLoad balancerTraffic enters here.Calls AI app.Layer 4 balancers route by IP and port; layer 7 balancers read HTTP and can route by path or header.–
AI appApp serviceLoad balancer forwards to it.Calls Semantic cache (checked first), Model.Little's law: throughput ≈ concurrency ÷ latency. 200 slots at 50 ms serve about 4,000 req/s.3 replicas × 500 slots · timeout 30 s
ModelLLM endpointAI app calls it.Latency has two parts: time to the first token, then a steady stream of tokens per second.400 streams · 4M input tokens/min
Semantic cacheSemantic cacheAI app checks it first.A semantic cache matches questions by meaning using embeddings, not exact text.10% hit rate

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