> Uh, why exactly do you think this is race-free?
>
> It looks fancy, but AFAICS the SELECT will return info that is correct
> as of its starting timestamp; which is not enough to guarantee that the
> INSERT won't conflict with another transaction doing the same thing
> concurrently.

How about:

INSERT INTO table SELECT 1, 'foo' WHERE NOT EXISTS (SELECT TRUE FROM table
WHERE pkcol=1 FOR UPDATE);

It's a lot more straightforward and has a FOR UPDATE.  Can this still cause
unique constraint failures?

Chris


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