RAG Core Tradeoffs
Overview
RAG systems face three persistent tensions that cannot be eliminated, only managed. Understanding these tradeoffs helps set realistic expectations and guides architectural decisions.
Tradeoff 1: Retrieval Precision vs. Generation Flexibility
Thing A: High Retrieval Precision
- Retrieves exactly the right documents
- Tight filtering and reranking
- Minimal noise passed to generator
Thing B: High Generation Flexibility
- Generator can work with imperfect retrieval
- Broader context windows
- Synthesis across many sources
Key Differences
- Precision-focused systems are brittle to ambiguous queries
- Flexibility-focused systems risk hallucination when retrieval is off-target
- Precision requires better retrievers; flexibility requires better generators
When Each Applies
- Prioritize precision: High-stakes, factual domains (medical, legal, financial)
- Prioritize flexibility: Exploratory, creative, or synthesis tasks
Tradeoff 2: Efficiency vs. Faithfulness
Thing A: High Efficiency
- Minimal retrieval calls
- Compressed context
- Fast inference
- Lower compute cost
Thing B: High Faithfulness
- Extensive retrieval coverage
- Full context preserved
- Multiple verification passes
- Higher grounding accuracy
Key Differences
- Efficiency optimizations often sacrifice verification steps
- Faithfulness requires computational overhead
- Caching helps efficiency but not faithfulness
When Each Applies
- Prioritize efficiency: Real-time applications, high-volume workloads
- Prioritize faithfulness: Any application where errors have consequences
Tradeoff 3: Modularity vs. Coordination
Thing A: High Modularity
- Retriever and generator are independent
- Easier to swap components
- Simpler debugging
- Clear responsibility boundaries
Thing B: High Coordination
- Joint training of retriever and generator
- End-to-end optimization
- Tighter feedback loops
- Better alignment between components
Key Differences
- Modularity enables iteration but limits joint optimization
- Coordination achieves better performance but is harder to maintain
- Hybrid systems try to balance both but add complexity
When Each Applies
- Prioritize modularity: Rapid prototyping, component reuse, maintainability
- Prioritize coordination: Maximum performance when resources allow
Meta-Observation
These tradeoffs are inherent to the architecture, not bugs to be fixed. Claiming to solve all three simultaneously is a red flag. Good system design makes explicit choices about which tradeoff to accept.
Related: 05-molecule—rag-architecture-taxonomy, 05-molecule—rag-evaluation-dimensions, 05-atom—rag-seven-failure-points