Simon Riggs <simon@2ndQuadrant.com> writes:
> On 11 October 2012 18:22, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> If it worked, I might be amenable to that, but it doesn't. You can't
>> trigger taking a new snapshot off whether we waited for a lock; that
>> still has race conditions, just ones that are not so trivial to
>> demonstrate manually. (The other transaction might have committed
>> microseconds before you reach the point of waiting for the lock.)
> So where's the race?
Same example as before, except that the exclusive-lock-holding
transaction commits (and releases its lock) between the time that the
other transaction takes its parse/plan snapshot and the time that it
takes AccessShare lock on the table.
regards, tom lane