Re: Making type Datum be 8 bytes everywhere

Em qui., 11 de set. de 2025 às 12:36, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> escreveu:

> Ranier Vilela <ranier(dot)vf(at)gmail(dot)com> writes:
> > Em qua., 10 de set. de 2025 às 17:35, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
> escreveu:
> >> This is silently assuming that sizeof(SortItem) is a multiple of
> >> alignof(Datum), which on a 32-bit-pointer platform is not true
> >> any longer. We ought to MAXALIGN the two occurrences of
> >> data->numrows * sizeof(SortItem).
>
> > We possibly have two more instances?
>
> > 1. Function ndistinct_for_combination
> (src/backend/statistics/mvdistinct.c)
> > - items = (SortItem *) palloc(numrows * sizeof(SortItem));
> > + items = (SortItem *) palloc(MAXALIGN(numrows * sizeof(SortItem)));
>
> > 2. Function build_distinct_groups (src/backend/statistics/mcv.c)
> > - SortItem *groups = (SortItem *) palloc(ngroups * sizeof(SortItem));
> > + SortItem *groups = (SortItem *) palloc(MAXALIGN(ngroups *
> > sizeof(SortItem)));
>
> Neither of those have any hazard, because they are not trying to
> allocate multiple arrays using address arithmetic. The part of
> build_sorted_items that was actually problematic was doing
>
> ptr += data->numrows * sizeof(SortItem);
>
> and then assuming that the result was suitably aligned to be
> cast to Datum*.
>
Thanks Tom, for double checking.

best regards,
Ranier Vilela