Re: BTScanOpaqueData size slows down tests

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
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