Negative Caching

Negative Caching in RAG (Retrieval-Augmented Generation) stores query-document pairs that resulted in no relevant matches to avoid repeated futile searches.

## What Is Negative Caching?

  • Purpose: Cache "no results found" responses for repeated queries
  • Mechanism: Store query fingerprints with negative hit flags
  • Benefit: Reduces unnecessary retrieval calls and latency
  • TTL: Time-limited to allow index updates to take effect

## Why Negative Caching Matters

Without negative caching, repeated queries for non-existent information trigger expensive retrieval operations every time.

RAG with Negative Caching:First Query: "Quantum teleportation protocol specs" │ ▼ [Vector Search] → No relevant docs │ ▼ [Add to negative cache] Second Query: "Quantum teleportation protocol specs" │ ▼ [Check negative cache] → HIT │ ▼ [Skip retrieval, return cached "no docs"] Saves: Vector DB query + embedding computation

Implementation Considerations:
| Parameter | Typical Value | Reason |
|-----------|---------------|--------|
| Cache TTL | 1-24 hours | Allow index updates |
| Key format | Query hash | Exact match lookup |
| Max entries | 10K-100K | Memory budget |
| Invalidation | On index update | Freshness |

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