Robert Haas <robertmhaas@gmail.com> writes:
> On Thu, Mar 1, 2018 at 2:03 AM, Craig Ringer <craig@2ndquadrant.com> wrote:
>> So I can't say it's definitely impossible. It seems astonishingly unlikely,
>> but that's not always good enough.
> Race conditions tend to happen a lot more often than one might think.
Just to back that up --- we've seen cases where people could repeatably
hit race-condition windows that are just an instruction or two wide.
The first one I came to in an idle archive search is
https://www.postgresql.org/message-id/15543.1130714273%40sss.pgh.pa.us
I vaguely recall others but don't feel like digging harder right now.
regards, tom lane
