Add a GUC to report whether data page checksums are enabled.

Bernd Helmle
Rename various "freeze multixact" variables

It seems to make more sense to use "cutoff multixact" terminology
throughout the backend code; "freeze" is associated with replacing of an
Xid with FrozenTransactionId, which is not what we do for MultiXactIds.

Andres Freund
Some adjustments by Álvaro Herrera
Remove `proc` argument from LockCheckConflicts

This has been unused since commit 8563ccae2caf.

Noted by Antonin Houska
Typo fix.

Etsuro Fujita
Documentation correction.

Etsuro Fujita
Fix typo in comment.

Ian Lawrence Barwick
Fix compiler warning in WaitForBackgroundWorkerStartup().

Per complaint from Andrew Gierth.
Fix two timeline handling bugs in pg_receivexlog.

When a timeline history file is fetched from server, it is initially created
with a temporary file name, and renamed to place. However, the temporary
file name was constructed using an uninitialized buffer. Usually that meant
that the file was created in current directory instead of the target, which
usually goes unnoticed, but if the target is on a different filesystem than
the current dir, the rename() would fail. Fix that.

The second issue is that pg_receivexlog would not take .partial files into
account when determining when scanning the target directory for existing
WAL files. If the timeline has switched in the server several times in the
last WAL segment, and pg_receivexlog is restarted, it would choose a too
old starting point. That's not a problem as long as the old WAL segment
exists in the server and can be streamed over, but will cause a failure if
it's not.

Backpatch to 9.3, where this timeline handling code was written.

Analysed by Andrew Gierth, bug #8453, based on a bug report on IRC.
Fix SSL deadlock risk in libpq

In libpq, we set up and pass to OpenSSL callback routines to handle
locking.  When we run out of SSL connections, we try to clean things
up by de-registering the hooks.  Unfortunately, we had a few calls
into the OpenSSL library after these hooks were de-registered during
SSL cleanup which lead to deadlocking.  This moves the thread callback
cleanup to be after all SSL-cleanup related OpenSSL library calls.
I've been unable to reproduce the deadlock with this fix.

In passing, also move the close_SSL call to be after unlocking our
ssl_config mutex when in a failure state.  While it looks pretty
unlikely to be an issue, it could have resulted in deadlocks if we
ended up in this code path due to something other than SSL_new
failing.  Thanks to Heikki for pointing this out.

Back-patch to all supported versions; note that the close_SSL issue
only goes back to 9.0, so that hunk isn't included in the 8.4 patch.

Initially found and reported by Vesa-Matti J Kari; many thanks to
both Heikki and Andres for their help running down the specific
issue and reviewing the patch.
pg_upgrade: fix C comment typo
pg_upgrade:  more C comment fixes
Don't allow system columns in CHECK constraints, except tableoid.

Previously, arbitray system columns could be mentioned in table
constraints, but they were not correctly checked at runtime, because
the values weren't actually set correctly in the tuple.  Since it
seems easy enough to initialize the table OID properly, do that,
and continue allowing that column, but disallow the rest unless and
until someone figures out a way to make them work properly.

No back-patch, because this doesn't seem important enough to take the
risk of destabilizing the back branches.  In fact, this will pose a
dump-and-reload hazard for those upgrading from previous versions:
constraints that were accepted before but were not correctly enforced
will now either be enforced correctly or not accepted at all.  Either
could result in restore failures, but in practice I think very few
users will notice the difference, since the use case is pretty
marginal anyway and few users will be relying on features that have
not historically worked.

Amit Kapila, reviewed by Rushabh Lathia, with doc changes by me.
doc: Clarify that file_fdw options require values.

Mike Blackwell and Robert Haas
pgbench: Tweak documentation.

Fabien COELHO
Use @libdir@ in both of regress/{input,output}/security_label.source

Though @libdir@ almost always matches @abs_builddir@ in this context,
the test could only fail if they differed.  Back-patch to 9.1, where the
test was introduced.

Hamid Quddus Akhtar
Fix pgindent comment breakage
Plug memory leak in range_cmp function.

B-tree operators are not allowed to leak memory into the current memory
context. Range_cmp leaked detoasted copies of the arguments. That caused
a quick out-of-memory error when creating an index on a range column.

Reported by Marian Krucina, bug #8468.
pgbench: Correct for bias in --rate schedule generation.

Previous code gave a mean delay 0.44% below target.  This change also
has the effect of increasing the maximum possible delay.

Fabien COELHO
Fix spurious warning after vacuuming a page on a table with no indexes.

There is a rare race condition, when a transaction that inserted a tuple
aborts while vacuum is processing the page containing the inserted tuple.
Vacuum prunes the page first, which normally removes any dead tuples, but
if the inserting transaction aborts right after that, the loop after
pruning will see a dead tuple and remove it instead. That's OK, but if the
page is on a table with no indexes, and the page becomes completely empty
after removing the dead tuple (or tuples) on it, it will be immediately
marked as all-visible. That's OK, but the sanity check in vacuum would
throw a warning because it thinks that the page contains dead tuples and
was nevertheless marked as all-visible, even though it just vacuumed away
the dead tuples and so it doesn't actually contain any.

Spotted this while reading the code. It's difficult to hit the race
condition otherwise, but can be done by putting a breakpoint after the
heap_page_prune() call.

Backpatch all the way to 8.4, where this code first appeared.
Fix erroneous statements about multiply specified JSON columns.

The behaviour in json_populate_record() and json_populate_recordset()
was changed during development but the docs were not.