slug: quack title: “Quack: the DuckDB wire protocol” description: “SQE speaks DuckDB’s Quack RPC protocol both ways: as a server (a DuckDB CLI queries SQE) and as a client (SQE’s quack_query() pulls from a remote Quack endpoint). run.sh proves the forward round-trip with a local DuckDB 1.5.3; the reverse is documented and verified.”

Quack: the DuckDB wire protocol

Quack is DuckDB’s RPC protocol. A DuckDB client can ATTACH 'quack:host:port' and query a remote engine as though it were a local database.

SQE speaks Quack both ways:

• As a server — a DuckDB client queries SQE’s catalogs over the Quack endpoint (quack_port in the coordinator config).
• As a client — SQE’s quack_query() table function pulls rows from a remote Quack endpoint (another SQE instance, or a DuckDB running quack_serve).

How it works

• The stack is a queryable SQE with a Nessie catalog and RustFS warehouse storage — the same base as the Nessie quickstart — plus the Quack endpoint enabled on the coordinator.
• Setting quack_port in the coordinator config is all that is needed to enable the endpoint. It serves a GET / identification probe and a POST /quack RPC surface.
• run.sh always validates the server-side probe (GET /). If a local DuckDB 1.5.3+ is on your PATH, it also seeds an Iceberg table in SQE and has DuckDB query it over Quack via the quack_query() table function.
• The reverse direction (SQE as a Quack client, pulling from a DuckDB quack_serve instance) is documented in the repo README and verified separately — SQE’s quack_query() function is available on every session.

Note that Quack is a pre-release protocol: DuckDB plans to stabilize it around v2.0, and the client extension ships from core_nightly. The round-trip works today (validated with duckdb 1.5.3) but is not a stable surface yet.

What it demonstrates

• Enabling SQE’s Quack server endpoint with a single config key.
• The GET / identification probe confirming the endpoint is live.
• A DuckDB client querying an SQE Iceberg table over the Quack protocol (forward round-trip).
• SQE as a Quack client: quack_query() pulling rows from a remote DuckDB quack_serve instance (reverse direction, documented and verified).

Status: experimental (2026-06-07).

Run it

Full config, docker compose, queries, and captured output are in the repo:

→ quickstart/quack/

cd quickstart/quack
cp .env.example .env
./run.sh