Bruce Momjian <bruce@momjian.us> writes:
> Tom Lane wrote:
>> But then what happens when you want to update a second tuple on the same
>> page? None of our existing plan types release and reacquire pin if they
>> don't have to, and I really doubt that we want to give up that
>> optimization.
> You will prune when you lock the page and at that point unless you got
> enough room for both tuples I doubt trying just before the second tuple
> is going to help.
No, you're missing the point completely. If the free space on the page
is, say, 1.5x the average tuple size, the code *won't* prune, and then
it will be stuck when it goes to do the second tuple update, because
there is no chance to reconsider the prune/no-prune decision after some
space is eaten by the first update.
regards, tom lane
