Add an example of attaching a default value to an updatable view.

This is probably the single most useful thing that ALTER VIEW can do,
particularly now that we have auto-updatable views.  So show an explicit
example.
Reduce log level of picksplit-doesn't-support-secondary-split whining.

This was agreed to back in 2007, but never actually done.

Josh Hansen
Document and clean up gistsplit.c.

Improve comments, rename some variables and functions, slightly simplify
a couple of APIs, in an attempt to make this code readable by people other
than its original author.

Even though this is essentially just cosmetic, back-patch to all active
branches, because otherwise it's going to make back-patching future fixes
in this file very painful.
Remove vestigial secondary-split support in gist_box_picksplit().

Not only is this implementation of secondary-split not better than the
default implementation in gistsplit.c, it's actually worse.  The gistsplit.c
code at least looks to see if switching the left and right sides would make
a better merge with the previously-split tuples, while this doesn't.

In any case it's rather useless to support secondary split only in an edge
case.  There used to be more complete support for it here (in chooseLR()),
but that was removed in commit 7f3bd86843e5aad84585a57d3f6b80db3c609916.
It appears to me though that the chooseLR() code was really isomorphic to
the default implementation, since it was still based on choosing the cheaper
way of adding two sub-split vectors that had been chosen without regard to
the primary split initially.  I think an implementation of secondary split
that could beat the default implementation would have to be pretty fully
integrated into the split algorithm, not plastered on at the end.

Back-patch to 9.2, but not further; previous branches have the chooseLR()
code which I don't feel a great need to mess with.  This is mainly so we
just have two behaviors and not three among the various branches (IOW, this
patch is cleanup for commit 7f3bd86843e5aad84585a57d3f6b80db3c609916's
incomplete removal of secondary-split support).
Remove useless picksplit-doesn't-support-secondary-split log spam.

This LOG message was put in over five years ago with the evident
expectation that we'd make all GiST opclasses support secondary split
directly.  However, no such thing ever happened, and indeed the number of
opclasses supporting it decreased to zero in 9.2.  The reason is that
improving on the default implementation isn't that easy --- the
opclass-specific code that did exist, before 9.2, doesn't appear to have
been any improvement over the default.

Hence, remove the message altogether.  There's certainly no point in
nagging users about this in released branches, but I doubt that we'll
ever implement complete opclass-specific support anyway.
Further cleanup of gistsplit.c.

After further reflection I was unconvinced that the existing coding is
guaranteed to return valid union datums in every code path for multi-column
indexes.  Fix that by forcing a gistunionsubkey() call at the end of the
recursion.  Having done that, we can remove some clearly-redundant calls
elsewhere.  This should be a little faster for multi-column indexes (since
the previous coding would uselessly do such a call for each column while
unwinding the recursion), as well as much harder to break.

Also, simplify the handling of cases where one side or the other of a
primary split contains only don't-care tuples.  The previous coding used a
very ugly hack in removeDontCares() that essentially forced one random
tuple to be treated as non-don't-care, providing a random initial choice of
seed datum for the secondary split.  It seems unlikely that that method
will give better-than-random splits.  Instead, treat such a split as
degenerate and just let the next column determine the split, the same way
that we handle fully degenerate cases where the two sides produce identical
union datums.
Include previous TLI in end-of-recovery and shutdown checkpoint records.

This isn't used for anything but a sanity check at the moment, but it could
be highly valuable for debugging purposes. It could also be used to recreate
timeline history by traversing WAL, which seems useful.
Fix checkpoint after fast promotion.

The intention was to request a regular online checkpoint immediately after
end of recovery, when performing "fast promotion". However, because the
checkpoint was requested before other backends were allowed to write WAL,
the checkpointer process performed a restartpoint rather than a checkpoint.

Delay the RequestCheckPoint call until after recovery has truly ended, so
that you get a real checkpoint.
Support unlogged GiST index.

The reason this wasn't supported before was that GiST indexes need an
increasing sequence to detect concurrent page-splits. In a regular WAL-
logged GiST index, the LSN of the page-split record is used for that
purpose, and in a temporary index, we can get away with a backend-local
counter. Neither of those methods works for an unlogged relation.

To provide such an increasing sequence of numbers, create a "fake LSN"
counter that is saved and restored across shutdowns. On recovery, unlogged
relations are blown away, so the counter doesn't need to survive that
either.

Jeevan Chalke, based on discussions with Robert Haas, Tom Lane and me.
Add noreturn attributes to some error reporting functions