Re: Potential G2-item cycles under serializable isolation

Oh! Gosh, yes, that DOES explain it. Somehow I had it in my head that both
RU and RC mapped to SI, and RR & Serializable mapped to SSI. That's the
case in YugabyteDB, but not here!

I'll also see about getting a version of these tests that doesn't involve
ON CONFLICT, in case that's relevant.

--Kyle

On Sun, May 31, 2020, 23:56 Peter Geoghegan <pg(at)bowt(dot)ie> wrote:

> On Sun, May 31, 2020 at 8:37 PM Kyle Kingsbury <aphyr(at)jepsen(dot)io> wrote:
> > This looks so weird that I assume I've *got* to be doing it wrong, but
> trawling
> > through the source code and pcap trace, I can't see where the mistake
> is. Maybe
> > I'll have fresher eyes in the morning. :)
>
> READ COMMITTED starts each command within a transaction with its own
> snapshot, much like Oracle:
>
> https://www.postgresql.org/docs/devel/transaction-iso.html
>
> There cannot be serialization errors with READ COMMITTED mode, and in
> general it is a lot more permissive. Probably to the point where it
> isn't sensible to test with Jepsen at all.
>
> It would make sense for you to test REPEATABLE READ isolation level
> separately, though. It implements snapshot isolation without the added
> overhead of the mechanisms that prevent (or are supposed to prevent)
> serialization anomalies.
>
> --
> Peter Geoghegan
>