Re: Unhappy about API changes in the no-fsm-for-small-rels patch

Andres Freund  writes:
> On 2019-04-23 15:46:17 +0530, Amit Kapila wrote:
>> If we invalidate it only when there's no space on the page, then when
>> should we set it back to available, because if we don't do that, then
>> we might miss the space due to concurrent deletes.

> Well, deletes don't traditionally (i.e. with an actual FSM) mark free
> space as available (for heap). I think RecordPageWithFreeSpace() should
> issue a invalidation if there's no FSM, and the block goes from full to
> empty (as there's no half-full IIUC).

Why wouldn't we implement this just as a mini four-entry FSM stored in
the relcache, and update the entries according to the same rules we'd
use for regular FSM entries?

			regards, tom lane