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Comment by mslot | Hacker News Reader

I don't think you can get around using 2PC in a distributed OLTP database, e.g. Spanner also uses 2PC for distributed transactions across shards. Fortunately, the overhead is not really that high because the prepare and commit messages are sent to all nodes in parallel. It only adds one extra network round trip. It does lower per session throughput a bit, but you can always get better throughput by creating more sessions.

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> Spanner runs consensus for each key range and does not need all nodes to be available to make progress also my understanding since again it has a leader for each key range writes scale better.

Spanner uses Paxos (consensus) for replication within a key range (shard), but two-phase commit across shards: https://ai.google/research/pubs/pub39966

Citus relies on PostgreSQL's streaming replication, which gives higher throughput than Paxos, but Paxos has better availability characteristics. On the other hand, Paxos with leader leases as used by Spanner is similar to streaming replication both in terms of performance characteristics and short downtime during failover.

It's not similar in infrastructure requirements though Spanner does not have 1/2 the nodes in standby mode for HA they are actually doing work.

Spanner runs consensus for each key range and does not need all nodes to be available to make progress also my understanding since again it has a leader for each key range writes scale better.

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