Re: WIP: Covering + unique indexes.

On Mon, Apr 2, 2018 at 4:27 PM, Alexander Korotkov
<a.korotkov@postgrespro.ru> wrote:
> I thought abut that another time and I decided that it would be safer
> to use 13th bit in index tuple flags.  There are already attempt to
> use whole 6 bytes of tid for not heap pointer information [1].  Thus, it
> would be safe to use 13th bit for indicating alternative offset meaning
> in pivot tuples, because it wouldn't block further work.  Revised patchset
> in the attachment implements it.

This is definitely not the only time someone has talked about this
13th bit -- it's quite coveted. It also came up with UPSERT, and with
WARM. That's just the cases that I can personally remember.

I'm glad that you found a way to make this work, that will keep things
flexible for future patches, and make testing easier. I think that we
can find a flexible representation that makes almost everyone happy.

I didn't have time to look at this properly today, but I will try to
do so tomorrow.