Re: [GENERAL] Non-overlapping updates blocking each other - Mailing list pgsql-general

> On Sat, Oct 14, 2017 at 10:30 AM, Seamus Abshere <seamus@abshere.net>
> > UPDATE [...] WHERE id BETWEEN 'ff000000-0000-0000-0000-000000000000' AND
> > 'ff0fffff-ffff-ffff-ffff-ffffffffffff'
> > and
> > UPDATE [...] WHERE id BETWEEN 'f8c00000-0000-0000-0000-000000000000' AND
> > 'f8ffffff-ffff-ffff-ffff-ffffffffffff'
> > Yet one blocks the other one. How is this possible?

On Sat, Oct 14, 2017, at 12:32 PM, Melvin Davidson wrote:
> More than likely, the optimizer has determined that a table scan is best,
> in which case it will use a table lock.
> You can also execute the following query and check the wait_event_type to
> verify.

hi Melvin,

Very interesting! The result:

wait_event      | page
wait_event_type | Lock

So I guess this means that the ids don't overlap, but they are sometimes
found in the same page, and the whole page gets locked?

Any narrative (pretending I don't know anything) would be very helpful.

Thanks!
Seamus

PS. I do a SELECT 1 FROM x WHERE [ID_RANGE] FOR UPDATE right before the
update, but that's to prevent a race condition. The id ranges still
don't overlap.