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As the linked page doesn't describe what it is: Bi-Directional Replication for PostgreSQL (Postgres-BDR, or BDR) is an asynchronous multi-master replication system for PostgreSQL, specifically designed to allow geographically distributed clusters. Supporting more than 48 nodes, BDR is a low overhead, low maintenance technology for distributed databases. [0]

[0]: https://2ndquadrant.com/en/resources/bdr/

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> Supporting more than 48 nodes

Hmm, on the mailing list announcement they claim 2-48 nodes.

EDIT: perhaps they're referring to support for read-replica's that can go beyond the 48 primaries.

https://www.postgresql.org/message-id/CAH%2BGA0qO0q9NJhKxaoo...

AFAIK there's no explicit limit per se - the BDR developers tested it with 48 nodes, but it will work with more nodes.

But there are things you'll probably run into - for example this only supports full mesh topology, i.e. each node speaks to every other node. So the more nodes you have, the higher the number of management connections.

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