On 3 October 2014 10:57, Peter Geoghegan <pg@heroku.com> wrote:
> On Fri, Oct 3, 2014 at 2:50 AM, Simon Riggs <simon@2ndquadrant.com> wrote:
>> My view is that I can't see the above use case from happening in real
>> situations, except by infrequent mistake. In most cases, unique
>> indexes represent some form of object identity and those don't change
>> frequently in the real world. So to be changing two unique fields at
>> the same time and it not representing some form of business process
>> error that people would like to see fail anyway, I'd be surprised by.
>
> Are we talking about two different things here?
>
> Unprincipled deadlocks can be seen without updating any constrained
> column in the UPSERT. The test-case that originally highlighted the
> issue only had one unique index, and it was *not* in the update's
> targetlist. See:
>
> https://wiki.postgresql.org/wiki/Value_locking#.22Unprincipled_Deadlocking.22_and_value_locking
I followed that to a wiki page, then clicked again to an old email. No
test case.
-- Simon Riggs http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services
