Selecting a vector database requires calculating the exact memory footprint of your embeddings before signing a contract. A standard 1536-dimension vector (common for OpenAI embeddings) using 32-bit floating-point numbers requires 6 KB of raw storage per vector. However, when you build a vector index like HNSW (Hierarchical Navigable Small World) for fast cosine similarity searches, the memory overhead can easily double. If you plan to upsert 10 million documents, you are not looking at 60 GB of storage; you need closer to 120 GB of high-speed RAM to keep query latencies under 50 milliseconds.
This memory demand makes the managed vs. self-hosted cost comparison critical. Managed serverless options charge strictly for write/read operations and storage, which is ideal for sporadic workloads. Conversely, self-hosting open-source engines on cloud VMs requires provisioning for peak load, meaning you pay for 100% of the RAM and CPU 24/7, even when query volume drops to zero.
Multi-tenancy requirements further complicate this math. If your application isolates customer data using a unique namespace, some managed providers charge a premium per active namespace, while others handle millions of namespaces with zero overhead. Before committing to an architecture, browse our directory of Vector Databases tools to compare how different engines handle index compression techniques like Scalar Quantization, which can slash your RAM costs by up to 75% at the expense of minor recall accuracy.