Previously, xpath() simply returned an empty array if the expression did
not yield a node set.  This is useless for expressions that return scalars,
such as one with name() at the top level.  Arrange to return the scalar
value as a single-element xml array, instead.  (String values will be
suitably escaped.)

This change will also cause xpath_exists() to return true, not false,
for such expressions.

Florian Pflug, reviewed by Radoslaw Smogura

Without this it's possible for the output to not be legal XML, as
illustrated by the added regression test cases.

NB: this change will need to be called out as an incompatibility in the
9.2 release notes, since it's possible somebody was relying on the old
behavior, even though it's clearly wrong.

Florian Pflug, reviewed by Radoslaw Smogura

This requires a new shared catalog, pg_shseclabel.

Along the way, fix the security_label regression tests so that they
don't monkey with the labels of any pre-existing objects.  This is
unlikely to matter in practice, since only the label for the "dummy"
provider was being manipulated.  But this way still seems cleaner.

KaiGai Kohei, with fairly extensive hacking by me.

libxml reports some errors (like invalid xmlns attributes) via the error
handler hook, but still returns a success indicator to the library caller.
This causes us to miss some errors that are important to report.  Since the
"generic" error handler hook doesn't know whether the message it's getting
is for an error, warning, or notice, stop using that and instead start
using the "structured" error handler hook, which gets enough information
to be useful.

While at it, arrange to save and restore the error handler hook setting in
each libxml-using function, rather than assuming we can set and forget the
hook.  This should improve the odds of working nicely with third-party
libraries that also use libxml.

In passing, volatile-ize some local variables that get modified within
PG_TRY blocks.  I noticed this while testing with an older gcc version
than I'd previously tried to compile xml.c with.

Florian Pflug and Tom Lane, with extensive review/testing by Noah Misch

Noah Misch diagnosed the buildfarm problems in the isolation tests
partly as failure to differentiate backends properly; the old code was
using backend IDs, which is not good enough because a new backend might
use an already used ID.  Use PIDs instead.

Also, the code was purposely careless about other concurrent activity,
because it isn't expected; and in fact, it doesn't affect the vast
majority of the time.  However, it can be observed that autovacuum can
block tables for long enough to cause sporadic failures.  The new code
accounts for that by ignoring locks held by processes not explicitly
declared in our spec file.

Author: Noah Misch

The previous value of 20ms is dangerously close to the time actually
spent just waiting for the deadlock to happen, so on occasion it causes
the test to fail simply because the other session didn't get to run
early enough, not managing to cause the deadlock that needs to be
detected.  With this new value, it's expected that most machines on
normal load will be able to pass the test.

Author: Noah Misch

These new files allow the new FK tests on isolationtester to pass on the
serializable and repeatable read isolation levels (which are untested
by the buildfarm).

Author: Kevin Grittner
Reviewed by Noah Misch

Subtransaction locks now released en masse at main commit, rather than
repeatedly re-scanning for locks as we ascend the nested transaction tree.
Split transaction state TBLOCK_SUBEND into two states, TBLOCK_SUBCOMMIT
and TBLOCK_SUBRELEASE to allow the commit path to be optimised using
the existing code in ResourceOwnerRelease() which appears to have been
intended for this usage, judging from comments therein.

1. In GetLockStatusData, avoid initializing instance before we've ensured
that the array is large enough.  Otherwise, if repalloc moves the block
around, we're hosed.

2. Add the word "Relation" to the name of some identifiers, to avoid
assuming that the fast-path mechanism will only ever apply to relations
(though these particular parts certainly will).  Some of the macros
could possibly use similar treatment, but the names are getting awfully
long already.

3. Add a missing word to comment in AtPrepare_Locks().

Reported by Peter Eisentraut.

Fujii Masao

Standby servers can now have WALSender processes, which can work with
either WALReceiver or archive_commands to pass data. Fully updated
docs, including new conceptual terms of sending server, upstream and
downstream servers. WALSenders terminated when promote to master.

Fujii Masao, review, rework and doc rewrite by Simon Riggs

This is more SQL-spec-compliant, more easily extensible, and better
performing than the old method of inventing special variables.

Pavel Stehule, reviewed by Shigeru Hanada and David Wheeler

Noah Misch.  Review and minor cosmetic changes by me.

Patch originally by Akira Kurosawa <kurosawa-akira@mxc.nes.nec.co.jp>.

When an AccessShareLock, RowShareLock, or RowExclusiveLock is requested
on an unshared database relation, and we can verify that no conflicting
locks can possibly be present, record the lock in a per-backend queue,
stored within the PGPROC, rather than in the primary lock table.  This
eliminates a great deal of contention on the lock manager LWLocks.

This patch also refactors the interface between GetLockStatusData() and
pg_lock_status() to be a bit more abstract, so that we don't rely so
heavily on the lock manager's internal representation details.  The new
fast path lock structures don't have a LOCK or PROCLOCK structure to
return, so we mustn't depend on that for purposes of listing outstanding
locks.

Review by Jeff Davis.

We already have similar functions for many other object types, including
operator classes, so it seems like we should have this one, too.

Extracted from a larger patch by Josh Kupershmidt

Move FileClose's decrement of temporary_files_size up, so that it will be
executed even if elog() throws an error.  This is reasonable since if the
unlink() fails, the fact the file is still there is not our fault, and we
are going to forget about it anyhow.  So we won't count it against
temp_file_limit anymore.

Update fileSize and temporary_files_size correctly in FileTruncate.
We probably don't have any places that truncate temp files, but fd.c
surely should not assume that.

The limit is enforced against the total amount of temp file space used by
each session.

Mark Kirkwood, reviewed by Cédric Villemain and Tatsuo Ishii

If a Var was used only in a GROUP BY expression, the previous
implementation would include the Var by itself (as well as the expression)
in the generated targetlist.  This wouldn't affect the efficiency of the
scan/join part of the plan at all, but it could result in passing
unnecessarily-wide rows through sorting and grouping steps.  It turns out
to take only a little more code, and not noticeably more time, to generate
a tlist without such redundancy, so let's do that.  Per a recent gripe from
HarmeekSingh Bedi.

There may be some other places where we should use errdetail_internal,
but they'll have to be evaluated case-by-case.  This commit just hits
a bunch of places where invoking gettext is obviously a waste of cycles.

Per discussion, these seem too technical to be worth translating.

Kevin Grittner

This function supports untranslated detail messages, in the same way that
errmsg_internal supports untranslated primary messages.  We've needed this
for some time IMO, but discussion of some cases in the SSI code provided
the impetus to actually add it.

Kevin Grittner, with minor adjustments by me

This fixes SSPI login failures showing "The function
requested is not supported", often showing up when connecting
to localhost. The reason was not properly updating the SSPI
handle when multiple roundtrips were required to complete the
authentication sequence.

Report and analysis by Ahmed Shinwari, patch by Magnus Hagander

This provides deterministic deadlock-detection ordering for new
isolation tests, fixing the sporadic failures in them.

Author: Noah Misch

The commit action of temporary tables is currently not cataloged, so
we can't easily show it.  The previous value was outdated from before
we had different commit actions.

GISTInsertStack.childoffnum used to mean "offset of the downlink in this
node, pointing to the child node in the stack". It's now replaced with
downlinkoffnum, which means "offset of the downlink in the parent of this
node". gistFindPath() already used childoffnum with this new meaning, and
had an extra step at the end to pull all the childoffnum values down one
node in the stack, to adjust the stack for the meaning that childoffnum had
elsewhere. That's no longer required.

The reason to do this now is this new representation is more convenient for
the GiST fast build patch that Alexander Korotkov is working on.

While we're at it, replace the linked list used in gistFindPath with a
standard List, and make gistFindPath() static.

Alexander Korotkov, with some changes by me.

First, when following a right-link, we incorrectly marked the current page
as the parent of the right sibling. In reality, the parent of the right page
is the same as the parent of the current page (or some page to the right of
it, gistFindCorrectParent() will sort that out).

Secondly, when we follow a right-link, we must prepend, not append, the right
page to our list of pages to visit. That's because we assume that once we
hit a leaf page in the list, all the rest are leaf pages too, and give up.

To hit these bugs, you need concurrent actions and several unlucky accidents.
Another backend must split the root page, while you're in process of
splitting a lower-level page. Furthermore, while you scan the internal nodes
to re-find the parent, another backend needs to again split some more internal
pages. Even then, the bugs don't necessarily manifest as user-visible errors
or index corruption.

While we're at it, make the error reporting a bit better if gistFindPath()
fails to re-find the parent. It used to be an assertion, but an elog() seems
more appropriate.

Backpatch to all supported branches.

There's a heuristic in estimate_rel_size() to clamp the minimum size
estimate for a table to 10 pages, unless we can see that vacuum or analyze
has been run (and set relpages to something nonzero, so this will always
happen for a table that's actually empty).  However, it would be better
not to do this for inheritance parent tables, which very commonly are
really empty and can be expected to stay that way.  Per discussion of a
recent pgsql-performance report from Anish Kejariwal.  Also prevent it
from happening for indexes (although this is more in the nature of
documentation, since CREATE INDEX normally initializes relpages to
something nonzero anyway).

Back-patch to 9.0, because the ability to collect statistics across a
whole inheritance tree has improved the planner's estimates to the point
where this relatively small error makes a significant difference.  In the
referenced report, merge or hash joins were incorrectly estimated as
cheaper than a nestloop with inner indexscan on the inherited table.
That was less likely before 9.0 because the lack of inherited stats would
have resulted in a default (and rather pessimistic) estimate of the cost
of a merge or hash join.

It previously said YES, but that is incorrect.

No code changes; just avoid blaming query_planner for things it doesn't
really do.

Also correct reporting of interval precision when field restrictions
are specified in the typmod.

Regular aggregate functions in combination with, or within the arguments
of, window functions are OK per spec; they have the semantics that the
aggregate output rows are computed and then we run the window functions
over that row set.  (Thus, this combination is not really useful unless
there's a GROUP BY so that more than one aggregate output row is possible.)
The case without GROUP BY could fail, as recently reported by Jeff Davis,
because sloppy construction of the Agg node's targetlist resulted in extra
references to possibly-ungrouped Vars appearing outside the aggregate
function calls themselves.  See the added regression test case for an
example.

Fixing this requires modifying the API of flatten_tlist and its underlying
function pull_var_clause.  I chose to make pull_var_clause's API for
aggregates identical to what it was already doing for placeholders, since
the useful behaviors turn out to be the same (error, report node as-is, or
recurse into it).  I also tightened the error checking in this area a bit:
if it was ever valid to see an uplevel Var, Aggref, or PlaceHolderVar here,
that was a long time ago, so complain instead of ignoring them.

Backpatch into 9.1.  The failure exists in 8.4 and 9.0 as well, but seeing
that it only occurs in a basically-useless corner case, it doesn't seem
worth the risks of changing a function API in a minor release.  There might
be third-party code using pull_var_clause.

This enables us to test that blocking commands (such as foreign keys
checks that conflict with some other lock) act as intended.  The set of
tests that this adds is pretty minimal, but can easily be extended by
adding new specs.

The intention is that this will serve as a basis for ensuring that
further tweaks of locking implementation preserve (or improve) existing
behavior.

Author: Noah Misch

assigned.