Matthew Woodcraft <matthew@woodcraft.me.uk> writes:
> In an INSERT, are the rows guaranteed to be inserted in the order that
> the source query returns its rows, for locking purposes?
I dunno that we "guarantee" that, but it's hard to see why the
code would behave any differently, at present.
> and I run two concurrent copies of
> INSERT INTO foo (SELECT n FROM ... ORDER BY n);
> is there any guarantee that I'll get a unique constraint violation
> rather than a deadlock?
Well, the issue there is not about the physical insertion order
but the order in which the uniqueness checks happen. I think
you'd be all right with a traditional-style PG index, but maybe
not with a deferrable unique constraint.
regards, tom lane