Databases

SQLite

An embedded serverless database in a single file: the most widely deployed database in the world.

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What it is

SQLite is a library, not a server. The database lives in one file and the app works with it directly, with no network or separate process. The code is in the public domain.

It supports full SQL, ACID transactions, indexes, JSON functions and FTS5 for full-text search. WAL mode allows concurrent reads during a write, but only one writer at a time.

SQLite is built into phones, browsers, Electron apps and thousands of programs. Increasingly it is used server-side for small and medium services and in edge variants (Turso, Cloudflare D1).

Use it when

  • Mobile and desktop apps, local storage.
  • Prototypes, tests, small sites and internal tools.
  • A file format for data exchange and single-node analytics.

Avoid it when

  • Many concurrent writes from different servers: you need a client-server database.
  • Highly available clusters with automatic failover.

Key concepts

Single file
The whole database in one portable file.
WAL mode
A log that lets readers work alongside a writer.
Dynamic typing
The value's type, not the column's, drives storage (type affinity).
FTS5
The full-text search module.

Example

WAL mode, a table and a simple select.

Interview questions

  1. 1. Why is SQLite called serverless?

    There is no separate server process: the app reads and writes the file through a library. No network setup, users or extra service are needed.

  2. 2. What are the concurrency limits?

    Many readers at once but only one writer. WAL mode and short transactions reduce locking, yet many writers need a different database.

  3. 3. How does SQLite's dynamic typing differ from other databases?

    The type belongs to the value, so you can store text in an INTEGER column. STRICT tables enable strict types.

Related technologies

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