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Database / DuckDB Interview questions

How does DuckDB differ from a traditional client-server database like PostgreSQL?

PostgreSQL runs as a standalone server process that client applications connect to over a network protocol (even if that network is just localhost), designed from the ground up around many concurrent clients, robust multi-user access control, and a row-oriented storage engine well suited to transactional workloads. DuckDB, in its traditional mode, runs embedded inside the calling application's own process with no separate server or network protocol involved.

DuckDB (embedded mode)PostgreSQL
Runs in-process; no separate server by default.Runs as a standalone server process.
Columnar, vectorized engine optimized for OLAP.Row-oriented engine optimized for OLTP.
Simple to embed in a single application/script.Built for many concurrent clients and robust access control.
Single-file persistence, trivially portable.Managed data directory requiring dedicated database administration.

Notably, this gap has started narrowing somewhat: DuckDB's newer Quack client-server protocol brings an optional, genuine client-server deployment mode to DuckDB for cases that want that model, while PostgreSQL's own ecosystem includes DuckDB-powered extensions for accelerating analytical queries. The core distinction in typical use, though, remains DuckDB's embedded-first design against PostgreSQL's server-first, multi-client design.

PostgreSQL, unlike DuckDB's traditional mode, is designed around:
Which engine is generally optimized for OLTP-style row-oriented transactional workloads?

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