Re: Strangeness with UNIQUE indexes and UTF-8

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 <pryzby(at)telsasoft(dot)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
>