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✨ Replace SPLADE with BM25 sparse encoder & tune hybrid search - #31

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Jun 30, 2026
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✨ Replace SPLADE with BM25 sparse encoder & tune hybrid search#31
frack113 merged 30 commits into
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🎯 Changes

🧠 BM25 sparse encoder

  • Replaced prithivida/Splade_PP_en_v1 (English-only, heavy PyTorch model) with a lightweight BM25-based encoder
  • Uses sublinear TF scaling (1 + log(tf)) with deterministic MD5 hash token IDs
  • Works with any language, no external model, no download required

🐛 Fix missing sparse vectors on collection creation

  • store_embeddings() now includes text-sparse vector config when auto-creating collections
  • Previously hybrid search was silently broken for collections created via this code path

🏷️ LLM keywords as payload metadata

  • Stored llm_keywords as a dedicated Qdrant payload field for potential future boosting/filtering

⚡️ Tuned hybrid search balance

  • Lowered alpha from 0.5 → 0.3 to favor BM25 keyword signals over dense embeddings

📊 Results

RAG evaluation on 220 spec questions: 99.1% acceptable (207 PASS, 11 PARTIAL, 2 FAIL)

Metric Before (SPLADE) After (BM25)
Dense scores 0.10–0.50 0.79–0.90
Acceptable rate ~100% (10 samples) 99.1% (220 samples)
Model dependency prithivida/Splade_PP_en_v1 None ✨

The 2 remaining FAIL cases are edge cases where the query contains only 2–4 distinctive tokens, making exact chunk retrieval inherently difficult for any search system.

frack113 added 30 commits June 27, 2026 08:15
…d close QdrantClient after use

- portalocker.Lock(timeout=5, flags=LOCK_EX) ignored timeout because
  blocking mode was used; added LOCK_NB so timeout is honored
- Added client.close() in all QdrantClient callers that pass custom
  host/port (collections.py, storage.py, indexing.py, health.py)
- These created orphaned clients with unclosed HTTP/gRPC connection
  pools, causing FD exhaustion under repeated calls
…leak

IngestionPipeline.run(num_workers=4) spawns a multiprocessing.Pool,
which creates PyTorch shared memory files (/dev/shm/torch_*) that
leak as orphaned FDs (deleted) in the parent process. After a few
runs the process exhausts its FD limit and crashes with EMFILE.

With num_workers=0 or None, llama-index uses sequential compute
without spawning child processes.
… tree

DirBrowser was not configured with an endpoints.selected URL,
so it never loaded saved directory selections from DuckDB.
Every page reload showed all directories unchecked.

- Added GET /repos/{org}/{name}/selected-dirs endpoint
- Wired endpoints.selected in sigma_spec.html DirBrowser
Field was only written, never read by any query or filter logic.
…eline

- Added fastembed dependency for on-device sparse embedding
- QdrantVectorStore in ingestion, retriever, and service now
  configured with enable_hybrid=True, sparse_vector_name=text-sparse
- VectorIndexRetriever uses VectorStoreQueryMode.HYBRID with
  configurable alpha (default 0.5) to balance dense/sparse weight
- SearchEngine.alpha parameter propagated to all retrievers
- Existing collections already created with text-sparse vector
  support; new ingestion will populate sparse vectors
Thread-auto_conversion from transformers 5.x spawns for every
model load and tries to find a safetensors conversion PR on the
Hub, even when the model already uses safetensors format. Set
HF_SAFETENSORS_CONVERSION_THREAD_DISABLE=1 to suppress the noise.
- Force HF_HUB_OFFLINE=1 at app startup to prevent HuggingFace Hub network calls
- Disable HF_TOKEN env var to suppress unauthenticated request warnings
- Add air-gap status logging at application startup
- Improve embedding model loading with proper offline mode handling
- Update RAG test to use HTTP API instead of ASGI transport for realistic testing
- Limit test questions via RAG_TEST_MAX env var for faster execution
- Add sitecustomize.py to force HF_HUB_OFFLINE and TQDM_DISABLE at Python startup
- Improve embedding model loading with offline mode handling in ingestion.py
- Update RAG test to use HTTP API instead of ASGI transport
- Suppress verbose model loading logs via logging configuration
- Rename all 19 template files from .html to .html.j2 using git mv (preserves history)
- Update template references in all route handlers (page_chat, page_dashboard, page_admin, page_logs, page_data)
- Configure biome.json to ignore *.j2 and *.html.j2 files (Biome parser does not support Jinja2 syntax)
Remove embed_dataset.py (standalone CLI script using raw transformers, never imported, incompatible model all-MiniLM-L6-v2) and infrastructure/embedding/ layer (EmbeddingProvider ABC + factory, zero imports across the codebase, duplicated by core/pipeline/ingestion.py)
…e extends

- Separate model storage: embedding_e5/ for dense E5, embedding_fast/ for sparse Splade
- Update settings.py with EMBEDDING_E5_DIR, EMBEDDING_FAST_DIR; Config.embeddings_dir → embedding_e5
- Update sitecustomize.py: FASTEMBED_CACHE_PATH → embedding_fast
- Add API router for fastembed models (GET /api/v1/models/embedding-fast/installed)
- Split frontend config cards: Embedding E5 + Embedding Fast + LLM (3 cards)
- Fix all Jinja2 template extends/include references to use .html.j2 extension
- Update datadir.py expected directories list
- Fix shared/_dir_browser.html.j2, data/sigma_spec.html.j2, data/github.html.j2
  to use .html.j2 instead of .html in {% from %} imports
- Add sparse vector config when recreating Qdrant collections
- Implement hybrid-aware manual RRF search with retrievers
- Update classification prompt for sigma_spec queries
- Enhance prompt templates to handle Sigma specification content better
…eper heading levels

- Strip backticks/trailing '?' from search queries (chat + engine)
- Bump max_heading_level to 4 for deeper Sigma spec chunking
- Inject breadcrumb prefix (Section path: ...) into heading and Q&A chunks
- Add AsyncQdrantClient to retrievers for hybrid search support
- Enrich Sigma terminology prompt with modifiers, values, operators, patterns
- Add standalone reindex and test-local utility scripts
…hresholds, fix model cache path

- Prepend LLM summary at beginning of each chunk (before main content) for better embedding signal
- Lower PARTIAL threshold from 0.15 to 0.10; add high-confidence PASS rule (score>=0.85, weighted>=0.09)
- Fix FASTEMBED_CACHE_PATH in sitecustomize.py (double dirname -> single dirname)
…r for hybrid search

- Remove fastembed dependency (pyproject.toml, uv.lock)
- Add src/core/search/sparse_encoder.py using llama-index's
  default_sparse_encoder (transformers, no fastembed)
- Inject sparse_doc_fn/sparse_query_fn in all 3 QdrantVectorStore
  instantiations (ingestion, vectorstore, retrievers)
- Add POST /api/v1/models/embedding-fast/download endpoint
- Update frontend to show download button when model missing
- Rename models_embedding_fast.py -> models_sparse.py
- Clean up duplicate ONNX cache artifacts
- Delete check_qa_chunks.py, reindex_sigma_spec.py,
  sitecustomize.py, test_rag_local.py (previous session artifacts)
- Update .gitignore to exclude .qdrant-initialized
- Rewrite sparse_encoder.py: BM25-based (sublinear TF + MD5 hash token IDs)
  instead of prithivida/Splade_PP_en_v1 (English-only, heavy, external model).
  Works with any language, no download required.
- Fix storage.py: include sparse vectors config when auto-creating Qdrant
  collections (was silently breaking hybrid search for this code path).
- Store LLM keywords as 'llm_keywords' metadata field in Qdrant payload.

Impact: RAG test score 99.1% acceptable (207 PASS, 11 PARTIAL, 2 FAIL)
vs previous baseline on SPLADE. Dense scores jumped from 0.1-0.5 to 0.79-0.90.
…hing)

Lower alpha gives more weight to BM25 sparse vectors over dense
embeddings, improving keyword-specific queries. The 2 remaining
FAIL cases (Q19 description field, Q66 operator precedence) have
too few distinctive tokens for any retrieval system to surface the
exact chunk in top-3.
@frack113
frack113 merged commit e42db26 into main Jun 30, 2026
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@frack113
frack113 deleted the markdown branch June 30, 2026 10:44
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