Re: Multi-Column List Partitioning

On Thu, Dec 9, 2021 at 11:24 AM Amit Langote <amitlangote09@gmail.com> wrote:
>
[....]
> On Mon, Dec 6, 2021 at 10:57 PM Nitin Jadhav
> <nitinjadhavpostgres@gmail.com> wrote:
> > > Looks difficult to understand at first glance, how about the following:
> > >
> > > if (b1->isnulls != b2->isnulls)
> > >    return false;
>
> I don't think having this block is correct, because this says that two
> PartitionBoundInfos can't be "logically" equal unless their isnulls
> pointers are the same, which is not the case unless they are
> physically the same PartitionBoundInfo.  What this means for its only
> caller compute_partition_bounds() is that it now always needs to
> perform partition_bounds_merge() for a pair of list-partitioned
> relations, even if they have exactly the same bounds.
>
> So, I'd suggest removing the block.
>

Agreed, I too realized the same; the check is incorrect and have noted
it for the next post. But note that, we need a kind of check here otherwise,
how could two bounds be equal if one has nulls and the other doesn't.
Also, we would have a segmentation fault in the next block while
accessing b2->isnulls if that is null.

I would suggest check like this:

if ((b1->isnulls == NULL)  != (b2->isnulls == NULL))
return false;

OR

if ((b1->isnulls)  ^ (b2->isnulls))
return false;

Regards,
Amul