Canton PQS (Participant Query Store)

Overview

PQS subscribes to a validator's transaction stream and projects contract data into a PostgreSQL database. Your backend then queries ledger state with standard SQL instead of walking the ACS over the Ledger API. It's the scalable read path for anything beyond simple per-contract lookups.

When to use PQS

Reach for PQS when you need:

• Filtered queries across many contracts (e.g. "all licenses expiring this month")
• Aggregations and reporting
• Full-text search or complex joins
• A read path that doesn't load the Ledger API (offload reads from the participant)

For a single known contract or a simple subscription, the Ledger API / ACS is enough — PQS shines at query complexity and volume.

How it stays in sync

PQS keeps its tables synchronized with the ledger: as contracts are created and archived, it inserts/updates the corresponding rows. Your SQL always reflects current ledger state (with a small propagation delay). Because it follows the same per-party transaction stream, it only ever contains contracts your party is a stakeholder of — privacy is preserved.