> 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.
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