RE: non-HOT update not looking at FSM for large tuple update

Hi,

>
> This patch fails to consider that len may be bigger than MaxHeapTupleSize *
> 0.98, which in this case triggers a reproducable
> PANIC:

Good catch! I've adapted the patch with your suggested fix.

>
> One different question I have, though, is why we can't "just" teach vacuum
> to clean up trailing unused line pointers. As in, can't we trim the line pointer
> array when vacuum detects that the trailing line pointers on the page are all
> unused?
>
> The only documentation that I could find that this doesn't happen is in the
> comment on PageIndexTupleDelete and PageRepairFragmentation, both not
> very descriptive on why we can't shrink the page->pd_linp array. One is
> "Unlike heap pages, we compact out the line pointer for the removed tuple."
> (Jan. 2002), and the other is "It doesn't remove unused line pointers! Please
> don't change this." (Oct. 2000), but I can't seem to find the documentation /
> conversations on the implications that such shrinking would have.
>

This is an interesting alternative indeed. I also can't find any documentation/conversation about this and the message is rather cryptic.
Hopefully someone on the list still remembers the reasoning behind this rather cryptic comment in PageRepairFragmentation.

-Floris