> You might think adding a UNIQUE index would cause the "losing" xact to get constraint errors, but instead both xacts succeed and no longer have a race conditi

> You might think adding a UNIQUE index would cause the "losing" xact to get constraint errors, but instead both xacts succeed and no longer have a race condition. This is not true. What happens is that the (sub)transaction that loses the race to the index is aborted: =# INSERT INTO foo (bar) (SELECT max(bar) + 1 FROM foo); ERROR: duplicate key value violates unique constraint "foo_bar_idx" DETAIL: Key (bar)=(2) already exists.