"Value locking" Wiki page

The current approach to "value locking" remains a controversial aspect
of my INSERT ... ON CONFLICT UPDATE patch. I must admit that this is a
very complicated area, and it's difficult to keep things straight,
particularly with the relevant discussion scattered all over the
place.

In the hope of unblocking things, I have created this Wiki page, which
details the advantages and disadvantages of all 3 approaches that have
been discussed, as suggested by myself and others:

https://wiki.postgresql.org/wiki/Value_locking

I actually think that we're only in disagreement on the extent to
which the stated advantages and disadvantages are useful or harmful.
So I think that at the moment this description is a reasonably
balanced handling of the issues. Please add any points that I missed.

This is by no means complete yet. There is pretty limited handling of
what I call "#3. "Promise" index tuples", because there was no
prototype version of that design, and there are many open questions
about how it would be implemented relative to the other 2 approaches.
Perhaps Andres or Simon would care to improve it. I think I've done a
better job of describing #2, Heikki's design - hardly surprising,
since there was a prototype that we discussed at length -  but I'd
appreciate it if other people would make sure that I have everything
right there. This is hopefully the beginning of working the issues
out. I have of course also described my own proposed design alongside
the others.

Please edit and add to my words as you see fit.
-- 
Peter Geoghegan