# Why Vectors Need a Database — Vector Databases

Source: https://www.geekswithgeeks.com/en/vector-databases/b-what

> See what a library does not give you and a database does.

## A search index is not yet a system

An index library such as FAISS can find nearest neighbours very fast, but a production application needs more: **durable storage** that survives restarts, **updates and deletes** as documents change, **metadata and filters** ("only this tenant", "only 2025"), **concurrent readers and writers**, **backups**, **access control**, **replication** for availability, **scaling** across machines and **monitoring**. A **vector database** (or a database with vector support) bundles these around one or more ANN indexes. Its basic unit is a **record** holding an **ID**, a **vector**, and **payload/metadata** (and often the original text). Queries combine **similarity** ("nearest to this vector") with **filters** ("where tenant = acme"), and return the top results with scores. Embeddings themselves are covered in the previous course; this course is about storing, searching and operating them.

## Vectors plus everything around them

A vector database stores vectors with their data and offers fast similarity search, filtering, updates and operations.

![Four parts: store, index, filter, operate.](assets/figures/vector-databases/section-1-map.svg) — Figure 1.1 — Store, index, filter and operate.

## A library versus a warehouse

A search index is like a very good card catalogue. A vector database is the whole warehouse: shelves, staff, security, back-office and delivery, with the catalogue inside.

## A record, conceptually

Every engine has its own names, but the shape is the same.

```json
{
  "id": "leave-policy-2025#chunk-3",
  "vector": [0.12, -0.08, 0.33, "... 768 numbers ..."],
  "payload": {
    "text": "Unused leave up to 5 days can be carried over.",
    "tenant": "acme", "year": 2025, "source": "hr-policy.pdf", "page": 4
  }
}
```

**Quiz:** What does a vector database add beyond an ANN index library?

- [ ] Free GPUs
- [ ] A new embedding model
- [x] Durability, updates, filters, access control, replication and operations
- [ ] Perfect recall always

*Answer:* Durability, updates, filters, access control, replication and operations. The database turns a fast index into a dependable system.