We do use ON CONFLICT… it doesn’t work because the index is both “good” and “bad” at the same time.
On Sun, Jun 6, 2021 at 2:03 PM Justin Pryzby <pry...@telsasoft.com> wrote: > On Sun, Jun 06, 2021 at 03:54:48AM -0700, Omar Kilani wrote: > > What I sort of don't get is... before we insert anything into these > > tables, we always check to see if a value already exists. And Postgres > > must be returning no results for some reason. So it goes to insert a > > duplicate value which somehow succeeds despite the unique index, but > > then a reindex says it's a duplicate. Pretty weird. > > In addition to the other issues, this is racy. > > You 1) check if a key exists, and if not then 2) INSERT (or maybe you > UPDATE if > it did exist). > > https://en.wikipedia.org/wiki/Time-of-check_to_time-of-use > > Maybe you'll say that "this process only runs once", but it's not hard to > imagine that might be violated. For example, if you restart a > multi-threaded > process, does the parent make sure that the child processes die before > itself > dying? Do you create a pidfile, and do you make sure the children are dead > before removing the pidfile ? > > The right way to do this since v9.6 is INSERT ON CONFLICT, which is also > more > efficient in a couple ways. > > -- > Justin >
