The Vector Database Index for RAG (2026)

Vector-DB choice is a stack question, not a leaderboard. Already on Postgres? pgvector. Want zero-ops? Pinecone. Open-source + hybrid? Weaviate or Qdrant. Here is a neutral index of the RAG/memory layer by store type, hosting model, and license — no prices, no benchmarks that go stale.

The matrix

Database	Type	Hosting	License	Best for
Pinecone	Dedicated vector DB	Managed	Proprietary	Zero-ops, fully-managed production vector search
Weaviate	Dedicated vector DB	Both	Open-source	Open-source vector search with built-in hybrid search and modules
Qdrant	Dedicated vector DB	Both	Open-source	High-performance, Rust-based search with heavy metadata filtering
Chroma	Embedded	Both	Open-source	Lightweight, developer-friendly prototyping and small RAG apps
Milvus	Dedicated vector DB	Both (Zilliz managed)	Open-source	Billion-scale vector search
pgvector	Database extension	Both (any Postgres)	Open-source	Adding vectors to an existing Postgres stack without a new database
Redis	Document/cache DB + vectors	Both	Source-available	Low-latency vector search alongside caching/session data
Elasticsearch / OpenSearch	Search engine + vectors	Both	Open-source (OpenSearch) / mixed	Combining full-text and vector (hybrid) search at scale
MongoDB Atlas Vector Search	Document/cache DB + vectors	Managed	Proprietary (Atlas)	Vectors stored next to your operational documents
Azure AI Search	Search engine + vectors	Managed	Proprietary	Vector and hybrid search inside the Azure ecosystem
Vertex AI Vector Search	Dedicated vector DB	Managed	Proprietary	Google Cloud-scale ANN search (formerly Matching Engine)
LanceDB	Embedded	Both	Open-source	Embedded, multimodal, on-disk vector storage

Quick picks

• You want zero-ops, fully managed vector search → Pinecone
• You already run Postgres and want one database → pgvector
• You want open-source with hybrid search → Weaviate or Qdrant
• You're prototyping a RAG app fast → Chroma or LanceDB
• You need billion-scale ANN → Milvus
• You want vectors next to operational data → MongoDB Atlas or Redis
• You need full-text + vector at scale → Elasticsearch / OpenSearch
• You're committed to Azure or Google Cloud → Azure AI Search / Vertex AI Vector Search

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📚 More from The 2026 AI Stack Index: Automation Tools · Agent Frameworks · Vector Databases · LLM Observability · LLM Gateways

This is a neutral, no-affiliate reference — no prices (they go stale), no rankings-for-pay. The full, always-updated interactive version with FAQs and the rest of the AI-stack indexes lives at aiprosol.com/vector-databases. Disclosure: I run Aiprosol, an automation consultancy — the index doesn't favour anyone.