Re: [WIP] [B-Tree] Retail IndexTuple deletion

On Tue, Jun 26, 2018 at 3:31 AM, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> bttargetdelete doesn't delete btree pages even if pages become empty.
> I think we should do that. Otherwise empty page never be recycled. But
> please note that if we delete btree pages during bttargetdelete,
> recyclable pages might not be recycled. That is, if we choose the
> target deletion method every time then the deleted-but-not-recycled
> pages could never be touched, unless reaching
> vacuum_cleanup_index_scale_factor. So I think we need to either run
> bulk-deletion method or do cleanup index before btpo.xact wraparound.

As you pointed out, we can certainly never fully delete or recycle
half-dead pages using bttargetdelete. We already need to make some
kind of compromise around page deletion, and it may not be necessary
to insist that bttargetdelete does any kind of page deletion. I'm
unsure of that, though.

--
Peter Geoghegan