[ztorkelson]

I actually don't have much hands-on experience with Postgres, so I can't speak to how it performs in practice.

My comment was highlighting that Postgres' implementation of SSI is at least a better starting point than most other purely pessimistic implementations of the serializable isolation level. It does not surprise me, however, to hear that there are still performance deficiencies in practice. For example, the Postgres implementation is imprecise, which will result in spurious transaction aborts (those will presumably be retried, but it comes at a cost to latency and throughput). And even though reads are optimistic (which will perform better than pessimistic concurrency control, if contention rates are sufficiently low), maintaining transaction dependency metadata can still have a non-negligible cost.

I also think Postgres suffers from other more dubious choices--like a lack of clustered indexes--which can exacerbate things.

My work in this area has focused on revisiting various architectural and implementation design decisions which have contributed to the current state of affairs. I think the relational data model is generally the right choice, but most relational databases have some godawful characteristics around performance, scalability, reliability, and programmability which limit their efficacy in practice.