# DuckDB: In-Process SQL OLAP Database for Files and Data Lakes

> DuckDB is an in-process columnar SQL database that queries Parquet, JSON, and S3 data lakes directly, with no server to run and MIT licensing throughout.

Published: 2026-07-14
URL: https://daniliants.com/insights/duckdb-in-process-sql-olap-database-for-files-and-data-lakes/
Tags: duckdb, open-source, developer-tools, local-first

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## Summary

DuckDB positions itself as an in-process, columnar SQL database ("OLAP") that queries Parquet, JSON, S3, and other data lake sources directly, without a separate server. It now also ships optional client-server support ("quack"), and the whole project (core plus extensions plus the DuckLake format) is MIT licensed.

## Key Insight

- **In-process, not client-server by default** - DuckDB runs embedded inside the calling process (like SQLite), so there is no daemon to manage for local analytics work; a client-server mode is now available as an add-on for shared or remote use cases.
- **Columnar engine built for analytics, not transactions** - optimized for scanning and aggregating large columns rather than row-by-row writes, and it spills to disk so workloads bigger than available RAM still complete instead of running out of memory.
- **Queries files and cloud storage without an import step** - can run SQL directly against Parquet, JSON, and S3-hosted data lakes, skipping the usual "load into a database first" workflow.
- **Extension-driven architecture** - many core features are themselves implemented as extensions, which is why the feature set (S3, JSON, spatial, and more) can grow without bloating the base install.
- **Fully permissive licensing** - DuckDB core, its extensions, and the DuckLake format are all MIT-licensed, which matters for anyone evaluating it for commercial or embedded redistribution.