Composite Index Chaining With Automatic Routing

via “multi-index query orchestration with hybrid retrieval strategies”

LlamaIndex is the leading document agent and OCR platform

Unique: Implements composable QueryEngine routers that can combine vector, keyword, graph, and structured queries through a unified interface with pluggable result merging strategies. Unlike LangChain's retriever composition (which chains retrievers sequentially), LlamaIndex's QueryEngine supports parallel multi-index querying with configurable fusion algorithms.

vs others: Enables true hybrid search with automatic result normalization and ranking, whereas LangChain requires manual result merging and score normalization across different retriever types.

via “composite-index chaining with automatic routing”

A library for efficient similarity search and clustering of dense vectors.

Unique: Provides pre-built composite index classes (IndexIVFPQ, IndexHNSWPQ) that automatically handle parameter passing and result routing between stages, eliminating manual pipeline orchestration. Enables composition of any two index types via the IndexPreTransform API for custom pipelines.

vs others: More convenient than manually chaining indices because parameter tuning and result routing are handled automatically; more flexible than single-index approaches because it enables joint optimization of filtering and refinement stages.