How-to guides

Focused guides that each walk through one task end to end — exposing a catalog, persisting state, serving over HTTP. Each assumes you’ve finished the tutorial and can already write and run a basic worker.

Not sure which function shape you need? Start with Function patterns — a runnable worker for each of the five shapes — then come back here for specific tasks.

Guides

• Expose a catalog — surface schemas, functions, tables, and views to DuckDB via ATTACH.
• Publish global functions — make selected functions callable without naming the attached catalog.
• Add a custom COPY format — implement COPY … FROM and COPY … TO for your own format or sink.
• Persist state across workers — shared, durable state for distributed aggregates.
• Serve over HTTP — run a worker as a network service.
• Use VGI from a Python app — drive a worker from your own program with the haybarn engine, no CLI.
• Authentication — gate an HTTP worker with bearer tokens or JWT/OAuth.
• Integrate with the optimizer — accept pushed-down filters and report column statistics.
• Cache results on the client — advertise TTLs and validators so repeat queries skip the worker entirely.

Each guide ends with a Next steps section that links onward to a concept page and the full reference for that topic.

Reference & tooling

• Function Metadata — describe your functions for introspection.
• CLI — invoke functions and inspect workers from the shell.

Next steps

• New here? Start with the tutorial.
• Want the “why” behind the API? See Concepts.
• Need exact signatures? See the API Reference.