Re: PG15 beta1 sort performance regression due to Generation context change

I wrote:
> However, here's a different idea: how badly do we need the "size"
> field in GenerationChunk?  We're not going to ever recycle the
> chunk, IIUC, so it doesn't matter exactly how big it is.  When
> doing MEMORY_CONTEXT_CHECKING we'll still want requested_size,
> but that's not relevant to performance-critical cases.

Refining that a bit: we could provide the size field only when
MEMORY_CONTEXT_CHECKING and/or CLOBBER_FREED_MEMORY are defined.
That would leave us with GenerationRealloc and GenerationGetChunkSpace
not being supportable operations, but I wonder how much we need either.

BTW, shouldn't GenerationCheck be ifdef'd out if MEMORY_CONTEXT_CHECKING
isn't set?  aset.c does things that way.

            regards, tom lane