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Even without external consistency, a I'm having trouble coming up with an ordering of the transactions that yields [1], [1, 10], [1, 1, 10].

Is that because PostgreSQL's "SERIALIZABLE" doesn't follow the "some serial order" definition? Or maybe I'm missing something else?

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Well, benmmurphy isn't talking about serializability (some correct ordering exists), but strict serializabilty (roughly: at least one correct ordering corresponds to wall clock order). PG does have the former, but not the latter.

Huh? The example is for PostgreSQL's "serializable" isolation level, and that's what I'm confused about.

Serializability should ensure that the outcome is equivalent to some serial execution. What serial execution of those five transactions yields [1], [1, 10], [1, 1, 10]?

But also, I just read that prior to PostgreSQL 9.1 (released in 2011), the "serializable" isolation level was actually just snapshot isolation (now called "repeatable read"). So maybe that's what benmmurphy is referring to?

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