Re: Lowering the ever-growing heap->pd_lower

On Tue, Mar 9, 2021 at 7:13 AM Matthias van de Meent
<boekewurm+postgres(at)gmail(dot)com> wrote:
> The shrinking of the line pointer array is already common practice in
> indexes (in which all LP_UNUSED items are removed), but this specific
> implementation cannot be used for heap pages due to ItemId
> invalidation. One available implementation, however, is that we
> truncate the end of this array, as mentioned in [1]. There was a
> warning at the top of PageRepairFragmentation about not removing
> unused line pointers, but I believe that was about not removing
> _intermediate_ unused line pointers (which would imply moving in-use
> line pointers); as far as I know there is nothing that relies on only
> growing page->pd_lower, and nothing keeping us from shrinking it
> whilst holding a pin on the page.

Sounds like a good idea to me.

--
Peter Geoghegan