Demystifying Postgres Foreign Key Constraints on Citus
summary
Citus 11.3 enforces foreign keys by creating local FKs on nodes so each FK is checked by the Postgres instance that holds the relevant shard. Distributed FKs require colocation and same distribution key (one FK becomes N shard-to-shard FKs) and Citus disallows actions that would make shard keys null, so no CASCADE/SET NULL for distributed→reference. Local↔local and reference↔reference FKs work normally; local↔distributed and reference→distributed FKs are currently unsupported.
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chapters (4)
- 0:00Introduction
- 2:02What is a Foreign Key?
- 7:49Challenges of Foreign Keys on a distributed environment
- 9:06How Citus approaches foreign keys
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