On 2025-Apr-02, Tom Lane wrote:
> Andres Freund <andres@anarazel.de> writes:
> > I'm a bit confused by the "MUST BE LAST" comment:
> > BTScanPosItem items[MaxTIDsPerBTreePage]; /* MUST BE LAST */
>
> Yeah, me too. It looks like it might've been intended to allow
> the items[] array to be only partially allocated. But as Peter
> says, we don't do that. Too long ago to be sure :=(
The mentioned commit (09cb5c0e7d6f) shows that we do partial memcpys, e.g.
+ memcpy(&so->markPos, &so->currPos,
+ offsetof(BTScanPosData, items[1]) +
+ so->currPos.lastItem * sizeof(BTScanPosItem));
That would obviously not work if this field weren't last. We still do
that, don't we? See btrestrpos().
--
Álvaro Herrera PostgreSQL Developer — https://www.EnterpriseDB.com/
"Before you were born your parents weren't as boring as they are now. They
got that way paying your bills, cleaning up your room and listening to you
tell them how idealistic you are." -- Charles J. Sykes' advice to teenagers
