Robert Haas <robertmhaas@gmail.com> writes:
> That's not what I'm saying. If we don't have the FSM, we have to
> check every page of the table. If there's a workload where that
> happens a lot on a table that is just under the size threshold for
> creating the FSM, then it's likely to be a worst case for this patch.
Hmm, you're assuming something not in evidence: why would that be the
algorithm? On a FSM-less table, I'd be inclined to just check the
last page and then grow the table if the tuple doesn't fit there.
This would, in many cases, soon result in a FSM being created, but
I think that's just fine. The point of the change is to optimize
for cases where a table *never* gets more than a few inserts. Not, IMO,
for cases where a table gets a lot of churn but never has a whole lot of
live tuples. In the latter scenario we are far better off having a FSM.
regards, tom lane