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04 — Patterns

Reusable RAG design patterns that cut across the architectures in 02_interview_bank/.

Contents

File	Pattern	When to Use
01-router-fallback.md	Router + Fallback	Route queries to cheapest retriever; fall back to expensive tiers only on failure
02-fan-out-fan-in.md	Fan-Out / Fan-In	Decompose multi-aspect queries into sub-queries, retrieve in parallel, merge with RRF
03-migration-path.md	Migration Path	Upgrade Naive → Advanced → Modular → Agentic incrementally with forcing functions
04-anti-patterns.md	Anti-Patterns	Five most common RAG design mistakes and how to avoid them

How to Use These Patterns

These patterns are not architectures (those are in 02_interview_bank/). They are design decisions that sit on top of any architecture:

A Modular RAG system can use the Router + Fallback pattern to pick its retrieval strategy
An Advanced RAG system can use Fan-Out to improve recall on multi-aspect queries
Any system benefits from the Migration Path framework when deciding which upgrade to make next
The Anti-Patterns apply to all architectures

Architecture selection guidance: cheatsheets/CHEATSHEET.md
Evaluation: 08_evaluation/
Production system design principles: 00_overview/system_design_principles.md