120 lines
2.8 KiB
Markdown
120 lines
2.8 KiB
Markdown
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# Hybrid RAG Search
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Hybrid search combines dense (semantic) and sparse (keyword) retrieval for better search quality than either method alone.
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## Overview
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| Method | Strengths | Weaknesses |
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|--------|-----------|------------|
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| **Dense (Semantic)** | Synonyms, meaning, paraphrasing | Rare terms, exact matches |
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| **Sparse (BM25)** | Exact terms, product codes, names | No semantic understanding |
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| **Hybrid** | Best of both | Slightly more computation |
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## How It Works
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```
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User Query
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│
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├──────────────────┐
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▼ ▼
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Dense Search Sparse Search
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(Weight: 0.7) (Weight: 0.3)
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│ │
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└────────┬─────────┘
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▼
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Reciprocal Rank Fusion
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│
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▼
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Optional Reranking
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│
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▼
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Final Results
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```
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**Reciprocal Rank Fusion (RRF):**
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```
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RRF_score(d) = Σ 1 / (k + rank_i(d))
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```
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## Configuration
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In `config.csv`:
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```csv
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name,value
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rag-hybrid-enabled,true
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rag-dense-weight,0.7
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rag-sparse-weight,0.3
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rag-top-k,10
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rag-rrf-k,60
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rag-reranker-enabled,false
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```
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## Weight Tuning
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| Content Type | Dense | Sparse | Use Case |
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|--------------|-------|--------|----------|
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| **Balanced** | 0.7 | 0.3 | General purpose |
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| **Semantic-Heavy** | 0.9 | 0.1 | Conversational, multilingual |
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| **Keyword-Heavy** | 0.4 | 0.6 | Technical docs, product catalogs |
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| **Equal** | 0.5 | 0.5 | When unsure |
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## Reranking
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Optional LLM-based reranking for highest quality:
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```csv
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name,value
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rag-reranker-enabled,true
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rag-reranker-model,quality
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rag-reranker-top-n,20
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```
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| Aspect | Without | With Reranking |
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|--------|---------|----------------|
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| Latency | ~50ms | ~500ms |
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| Quality | Good | Excellent |
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| Cost | None | LLM API cost |
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**Use for:** Legal, medical, financial, compliance-critical queries.
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## Usage
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Hybrid search is automatic when enabled. No code changes needed:
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```basic
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USE KB "company-policies"
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' Queries automatically use hybrid search
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```
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## Performance
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| Metric | Target |
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|--------|--------|
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| MRR (Mean Reciprocal Rank) | > 0.7 |
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| Recall@10 | > 0.9 |
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| Latency P95 | < 200ms |
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| Cache Hit Rate | > 40% |
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### Caching
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```csv
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name,value
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rag-cache-enabled,true
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rag-cache-ttl,3600
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rag-cache-max-size,10000
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```
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## Troubleshooting
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| Issue | Solution |
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|-------|----------|
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| Poor results | Adjust weights for content type |
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| High latency | Reduce `rag-top-k`, enable caching, disable reranking |
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| Missing expected results | Check document indexed, verify no filters excluding it |
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## See Also
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- [Semantic Search](../chapter-03/semantic-search.md) - Dense search details
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- [Document Indexing](../chapter-03/indexing.md) - How documents are processed
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- [Knowledge Base](./knowledge-base.md) - KB overview
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