Vector DB Selection — Qdrant primary, Pinecone fallback

Chose self-hosted Qdrant as primary with managed Pinecone as fallback, plus a candidate → stable index promotion so a bad re-index never reaches users.

Context: a RAG system needed reliable, cost-controlled retrieval without vendor lock-in. Decision: Qdrant for cost and control, Pinecone as a managed safety net, and a candidate→stable promotion flow for safe re-indexing. Trade-off: a bit more indexing machinery for zero-downtime retraining and provider independence.