Easy Vector DB Question 37 of 223

What is an index in a vector database?

GenAI / LLM · Speak this in 60–90 seconds · Faridabad & Delhi NCR

Without indexScan every row

With indexJump to keys

CostWrites slower

An index is the data structure that makes similarity search fast, such as HNSW or IVF.

LLMs use tokens (not full words) because it helps them:

Vector DB questions separate

people who only read docs from people who shipped.

Keep it short, concrete,

and tied to GenAI / LLM work.

Stable token IDs

Each piece maps to a number the network can learn.

Fits the model

Fixed pieces are what transformers expect as input.

Before you speak the answer, walk the interviewer through these steps:

1
An index is the
data structure that makes similarity search fast, such as HNSW or IVF.
2
Without an index, every
query would scan all vectors.
3
Indexes trade a little
recall for much lower latency.
4
Give an example
One tiny concrete case you can say aloud.
5
Common mistake
What juniors usually get wrong.
6
Close
When you pick this over the alternative.

Here's a short line you can speak, broken into clear beats:

Say this line

“Without an index, every query would scan all vectors.”

Break into beats

Withoutanindexeveryquerywould

Speaking order

2987408337471632900

Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.

An index is the data structure that makes similarity search fast, such as HNSW or IVF. Without an index, every query would scan all vectors.