Architectural taxonomy: four shapes of vector DB
Every vector database fits one of four architectural shapes. The shape matters more than the vendor name — it determines your ops surface area, your blast radius, your portability story, and your cost model.
**Shape 1: managed serverless.** Pinecone, Weaviate Cloud, Qdrant Cloud Serverless, Zilliz Cloud Serverless, Chroma Cloud, Turbopuffer. You pay per-vector or per-storage + per-query; the vendor handles scaling, replication, backup, upgrades. Lowest ops overhead, highest unit cost at scale, vendor-lock on data shape and query API.
**Shape 2: managed dedicated.** Pinecone Pod-based, Weaviate Enterprise SaaS, Qdrant Premium, Zilliz Dedicated, Elastic Cloud, AWS OpenSearch Service, Vespa Cloud. You provision specific instance sizes, pay hourly/monthly per instance regardless of utilization. Predictable cost, more knobs to tune, still vendor-managed.
**Shape 3: self-host open-source.** Qdrant, Milvus, Weaviate, Chroma server, Elasticsearch, OpenSearch, Vespa, Typesense — all open-source, all runnable on your own Kubernetes/VMs. Lowest dollar cost, highest ops cost, full data sovereignty, required for air-gapped deployments. Same software as the managed tier in most cases.
**Shape 4: in-process library or extension.** FAISS (library), Chroma embedded (Python in-process), pgvector (Postgres extension). No separate service, runs in your existing process or DB. Lowest latency, lowest ops, lowest portability — your application code and your vector store are coupled.
**Verdict on shapes**: greenfield SaaS → shape 1 (serverless) to ship fast. Postgres shop → shape 4 (pgvector) to eliminate infrastructure. Air-gapped/regulated → shape 3 (self-host). Billion-vector scale → shape 1 or 3 with capacity planning. Sub-millisecond latency requirement → shape 4 (FAISS or pgvector with HNSW).