Re: SERIALIZABLE and INSERTs with multiple VALUES

I've pushed a simplified (no refactoring) version of the fix proposed
by Thomas and Peter, so that we have some kind of fix in place for
tomorrow's releases.  I think further improvement along the lines
suggested by Kevin can wait till later.

I noticed that the ON CONFLICT DO NOTHING and ON CONFLICT DO UPDATE cases
are now not terribly consistent about what to do with self-conflicting
insertions.  The examples memorialized in commit a6c0a5b6e are

insert into selfconflict values (1,1), (1,2) on conflict do nothing;
-- succeeds, inserting the first row and ignoring the second

insert into selfconflict values (4,1), (4,2) on conflict(f1) do update set f2 = 0;
ERROR:  ON CONFLICT DO UPDATE command cannot affect row a second time
HINT:  Ensure that no rows proposed for insertion within the same command have duplicate constrained values.

I think that if we believe the first behavior is correct, then the second
behavior is a bug; what that command should do is to insert a single row
containing (4,0).  However, that behavior is the same across all isolation
levels, and it was like that before today's patches, so I didn't undertake
to do anything about it right now.

            regards, tom lane