PG ecosystem actually has multiple shared nothing cluster implementations, example is www.citusdata.com, unlike RAC, where masters need to sync to accept writes, so technically write load is not distributted across servers.
Re:Foundation DB Record Layer SQL API
by mike_hearn on Saturday May 10, 2025 @03:52AM
(#43943948)
Citus is great but it's just sharding. Only some very specific use cases fit within those limits, and there are cost issues too (being ha requires replicas of each node etc). RAC masters don't need to sync writes to each other, that's not how it works. Every node can be writing independently, they only communicate when one node has exclusive ownership over a block another node needs to write to, and the transfer then occurs peer to peer over rdma. But if writes are scattered they work independently.
> they only communicate when one node has exclusive ownership over a block another node needs to write to
and it needs to communicate that he has exclusive ownership, and also after each writes you need to invalidate cached data on other nodes.
A RAC cluster is multi-write master, and each node stores a subset of the data. You can then add as many read caches (not replicas) as you need, and they'll cache only the hot data blocks.
So they're not quite the same thing in that sense.