Kevin Grittner wrote:
> > If your query involves foreign scans on two foreign tables on the
> > same foreign server, these should always see the same snapshot,
> > because that's how it works with two scans in one query on local
> > tables.
> That makes sense.
> > So I think it should be REPEATABLE READ in all cases -
> > SERIALIZABLE is not necessary as long as all you do is read.
> That depends on whether you only want to see states of the database
> which are consistent with later states of the database and any
> invariants enforced by triggers or other software. See this example
> of how a read-only transaction can see a bogus state at REPEATABLE
> READ or less strict transaction isolation:
> Perhaps if the transaction using the pgsql_fdw is running at the
> SERIALIZABLE transaction isolation level, it should run the queries
> at the that level, otherwise at REPEATABLE READ.
I read the example carefully, and it seems to me that it is necessary
for the read-only transaction (T3) to be SERIALIZABLE so that
T1 is aborted and the state that T3 saw remains valid.
If I understand right, I agree with your correction.
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