Re: [HACKERS] [WIP] Effective storage of duplicates in B-tree index.

On Fri, Nov 15, 2019 at 5:02 PM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> What I saw suggests that we will need to remove the new "postingoff"
> field from xl_btree_insert. (We can create a new XLog record for leaf
> page inserts that also need to split a posting list, without changing
> much else.)

Attached is v24. This revision doesn't fix the problem with
xl_btree_insert record bloat, but it does fix the bitrot against the
master branch that was caused by commit 50d22de9. (This patch has had
a surprisingly large number of conflicts against the master branch
recently.)

Other changes:

* The pageinspect patch has been cleaned up. I now propose that it be
committed alongside the main patch.

The big change here is that posting lists are represented as an array
of TIDs within bt_page_items(), much like gin_leafpage_items(). Also
added documentation that goes into the ways in which ctid can be used
to encode information (arguably some of this should have been included
with the Postgres 12 B-Tree work).

* Basic tests that cover deduplication within unique indexes. We ought
to have code coverage of the case where _bt_check_unique() has to step
right (actually, we don't have that on the master branch either).

--
Peter Geoghegan