Notes
Indexes make database queries fast. Most relational databases use B-trees, which support exact lookups (find user with email X) and range queries (find all orders between date A and date B). Hash indexes are faster for exact matches but can’t do range queries.
There are external systems that go beyond what the primary DB provider has. Elasticsearch is the go-to for full-text search. PostGIS in Postgres is popular for geospatial queries. Such extensions typically sync from your primary DB and so the search index will lag slightly behind. However, the increased functionality is usually worth it.
References
- Core Concepts for System Design Interviews. www.hellointerview.com . Accessed Jun 6, 2026.