This function could often be seen in profiles of vacuum and could often
be a significant bottleneck during recovery. The problem was that a qsort
was performed in order to sort an array of item pointers in reverse offset
order so that we could use that to safely move tuples up to the end of the
page without overwriting the memory of yet-to-be-moved tuples. i.e. we
used to compact the page starting at the back of the page and move towards
the front. The qsort that this required could be expensive for pages with
a large number of tuples.

In this commit, we take another approach to tuple compactification.

Now, instead of sorting the remaining item pointers array we first check
if the array is presorted and only memmove() the tuples that need to be
moved. This presorted check can be done very cheaply in the calling
functions when the array is being populated. This presorted case is very
fast.

When the item pointer array is not presorted we must copy tuples that need
to be moved into a temp buffer before copying them back into the page
again. This differs from what we used to do here as we're now copying the
tuples back into the page in reverse line pointer order. Previously we
left the existing order alone.  Reordering the tuples results in an
increased likelihood of hitting the pre-sorted case the next time around.
Any newly added tuple which consumes a new line pointer will also maintain
the correct sort order of tuples in the page which will also result in the
presorted case being hit the next time.  Only consuming an unused line
pointer can cause the order of tuples to go out again, but that will be
corrected next time the function is called for the page.

Benchmarks have shown that the non-presorted case is at least equally as
fast as the original qsort method even when the page just has a few
tuples. As the number of tuples becomes larger the new method maintains
its performance whereas the original qsort method became much slower when
the number of tuples on the page became large.

Author: David Rowley
Reviewed-by: Thomas Munro
Tested-by: Jakub Wartak
Discussion: https://postgr.es/m/CA+hUKGKMQFVpjr106gRhwk6R-nXv0qOcTreZuQzxgpHESAL6dw@mail.gmail.com

ALTER TABLE commands in an extension script are added to an event
trigger command list; but starting with commit b5810de3 they do so in
a memory context that's too short-lived, so when execution ends and time
comes to use the entries, they've already been freed.

(This would also be a problem with ALTER TABLE commands in a
multi-command query string, but these serendipitously end in
PortalContext -- which probably explains why it took so long for this to
be reported.)

Fix by using the memory context specifically set for that, instead.

Backpatch to 13, where the aforementioned commit appeared.

Reported-by: Philippe Beaudoin
Author: Jehan-Guillaume de Rorthais <jgdr@dalibo.com>
Discussion: https://postgr.es/m/20200902193715.6e0269d4@firost

Reporting this has been rather useful in some recent recovery speedup
work.  It also seems like something that will be useful to the average DBA
too.

Author: David Rowley
Reviewed-by: Thomas Munro
Discussion: https://postgr.es/m/CAApHDvqYVORiZxq2xPvP6_ndmmsTkvr6jSYv4UTNaFa5i1kd%3DQ%40mail.gmail.com

This expands on the work done in d2d8a229 and allows incremental sort
to be considered during create_window_paths().

Author: David Rowley
Reviewed-by: Daniel Gustafsson, Tomas Vondra
Discussion: https://postgr.es/m/CAApHDvoOHobiA2x13NtWnWLcTXYj9ddpCkv9PnAJQBMegYf_xw%40mail.gmail.com

Introduced in 0aa8f764.

MSVC warned about performing 32-bit bit shifting when it appeared like we
might like a 64-bit result.  We did, but it just so happened that none of
the calls to this function could have caused the 32-bit shift to overflow.

Here we just cast the constant to int64 to make the compiler happy.

Discussion: https://postgr.es/m/CAApHDvofA_vsrpC13mq_hZyuye5B-ssKEaer04OouXYCO5-uXQ@mail.gmail.com

A walsender process that has executed a SQL command left the text of
that command in pg_stat_activity.query indefinitely, which is quite
confusing if it's in RUNNING state but not doing that query.  An easy
and useful fix is to treat replication commands as if they were SQL
queries, and show them in pg_stat_activity according to the same rules
as for regular queries.  While we're at it, it seems also sensible to
set debug_query_string, allowing error logging and debugging to see
the replication command.

While here, clean up assorted silliness in exec_replication_command:

* The SQLCmd path failed to restore CurrentMemoryContext to the caller's
value, and failed to delete the temp context created in this routine.
It's only through great good fortune that these oversights did not
result in long-term memory leaks or other problems.  It seems cleaner
to code SQLCmd as a separate early-exit path, so do it like that.

* Remove useless duplicate call of SnapBuildClearExportedSnapshot().

* replication_scanner_finish() was never called.

None of those things are significant enough to merit a backpatch,
so this is for HEAD only.

Discussion: https://postgr.es/m/880181.1600026471@sss.pgh.pa.us

A pre-commit review had reported the problem, but the fix reached only
v10 and earlier.  Back-patch to v11.

Discussion: https://postgr.es/m/20200423.140546.1055476118690602079.horikyota.ntt@gmail.com

Author: Naoki Nakamichi
Discussion: https://postgr.es/m/b6919d145af00295a8e86ce4d034b7cd@oss.nttdata.com

3c840464 is the original commit that introduced index_set_state_flags(),
where the presence of SnapshotNow made necessary the use of an in-place
update.  SnapshotNow has been removed in 813fb031, so there is no actual
reasons to not make this operation transactional.

Note that while making the operation more robust, using a transactional
operation in this routine was not strictly necessary as there was no use
case for it yet.  However, some future features are going to need a
transactional behavior, like support for CREATE/DROP INDEX CONCURRENTLY
with partitioned tables, where indexes in a partition tree need to have
all their pg_index.indis* flags updated in the same transaction to make
the operation stable to the end-user by keeping partition trees
consistent, even with a failure mid-flight.

REINDEX CONCURRENTLY uses already transactional updates when swapping
the old and new indexes, making this change more consistent with the
index-swapping logic.

Author: Michael Paquier
Reviewed-by: Anastasia Lubennikova
Discussion: https://postgr.es/m/20200903080440.GA8559@paquier.xyz

If there are no objects of a certain type, there is no need to do an
allocation for a set of DumpableObject items.  The previous coding did
an allocation of 1 byte instead as per the fallback of pg_malloc() in
the event of an allocation size of zero.  This assigns NULL instead for
a set of dumpable objects.

A similar rule already applied to findObjectByOid(), so this makes the
code more defensive as we would just fail with a pointer dereference
instead of attempting to use some incorrect data if a non-existing,
positive, OID is given by a caller of this function.

Author: Daniel Gustafsson
Reviewed-by: Julien Rouhaud, Ranier Vilela
Discussion: https://postgr.es/m/26C43E58-BDD0-4F1A-97CC-4A07B52E32C5@yesql.se

transformCreateStmt() adjusts the transformed statement's RangeVar
to specify the target schema explicitly, for the express reason
of making sure that auxiliary statements derived by parse
transformation operate on the right table.  But the refactoring
I did in commit 50289819 got this wrong and passed the untransformed
RangeVar to expandTableLikeClause().  This could lead to assertion
failures or weird misbehavior if the wrong table was accessed.

Per report from Alexander Lakhin.  Like the previous patch, back-patch
to all supported branches.

Discussion: https://postgr.es/m/05051f9d-b32b-cb35-6735-0e9f2ab86b5f@gmail.com

We use the timestamp of the global statfile if we are not able to
determine it for a particular database in case the entry for that database
doesn't exist. However, we were using it even when the statfile is
corrupt.

As there is no user reported issue and it is not clear if there is any
impact of this on actual application so decided not to backpatch.

Reported-by: Amit Kapila
Author: Amit Kapila
Reviewed-by: Sawada Masahiko, Magnus Hagander and Alvaro Herrera
Discussion: https://postgr.es/m/CAA4eK1J3oTJKyVq6v7K4d3jD+vtnruG9fHRib6UuWWsrwAR6Aw@mail.gmail.com

In the passing, fix a typo in pgoutput.c.

Reported-by: Tomas Vondra
Author: Tomas Vondra
Reviewed-by: Dilip Kumar
Discussion: https://postgr.es/m/20200909084353.pncuclpbwlr7vylh@development

The preallocation logic is only useful for HashAgg, so disable it when
sorting.

Also, adjust an out-of-date comment.

Reviewed-by: Peter Geoghegan
Discussion: https://postgr.es/m/CAH2-Wzn_o7tE2+hRVvwSFghRb75AJ5g-nqGzDUqLYMexjOAe=g@mail.gmail.com
Backpatch-through: 13

The bgwriter, checkpointer, walwriter, and walreceiver processes
claimed to allow SIGQUIT "at all times".  In reality SIGQUIT
would get re-blocked during error recovery, because we didn't
update the actual signal mask immediately, so sigsetjmp() would
save and reinstate a mask that includes SIGQUIT.

This appears to be simply a coding oversight.  There's never a
good reason to hold off SIGQUIT in these processes, because it's
going to just call _exit(2) which should be safe enough, especially
since the postmaster is going to tear down shared memory afterwards.
Hence, stick in PG_SETMASK() calls to install the modified BlockSig
mask immediately.

Also try to improve the comments around sigsetjmp blocks.  Most of
them were just referencing postgres.c, which is misleading because
actually postgres.c manages the signals differently.

No back-patch, since there's no evidence that this is causing any
problems in the field.

Discussion: https://postgr.es/m/CALDaNm1d1hHPZUg3xU4XjtWBOLCrA+-2cJcLpw-cePZ=GgDVfA@mail.gmail.com

The stats target can be set since commit d06215d0, but wasn't shown by
psql.

Author: Justin Pryzby <justin@telsasoft.com>
Discussion: https://postgr.es/m/20200831050047.GG5450@telsasoft.comReviewed-by: Georgios Kokolatos <gkokolatos@protonmail.com>
Reviewed-by: Tatsuro Yamada <tatsuro.yamada.tf@nttcom.co.jp>

Currently, no useful trace is left in the logs when the postmaster
is forced to use SIGKILL to shut down children that failed to respond
to SIGQUIT.  Some questions were raised about how often that scenario
happens in the buildfarm, so let's add a LOG-level message showing
that it happened.

Discussion: https://postgr.es/m/1850884.1599601164@sss.pgh.pa.us

Although 58c6fecc fixed the case for SIGQUIT, we were still calling
proc_exit() from signal handlers for SIGTERM and timeout failures in
ProcessStartupPacket.  Fortunately, at the point where that code runs,
we haven't yet connected to shared memory in any meaningful way, so
there is nothing we need to undo in shared memory.  This means it
should be safe to use _exit(1) here, ie, not run any atexit handlers
but also inform the postmaster that it's not a crash exit.

To make sure nobody breaks the "nothing to undo" expectation, add
a cross-check that no on-shmem-exit or before-shmem-exit handlers
have been registered yet when we finish using these signal handlers.

This change is simple enough that maybe it could be back-patched,
but I won't risk that right now.

Discussion: https://postgr.es/m/1850884.1599601164@sss.pgh.pa.us

Thinko in 40b3e2c2.
Reported-by: "Wang, Shenhao" <wangsh.fnst@cn.fujitsu.com>
Discussion: https://postgr.es/m/ed98706b82694b57a8c0d339a10732aa@G08CNEXMBPEKD06.g08.fujitsu.local

We were decoding empty transactions via streaming APIs added in commit
45fdc973 even when the user used the option 'skip-empty-xacts'. The APIs
makes no effort to skip empty xacts under the assumption that we will
never try to stream such transactions. However, that is not true because
we can pick to stream a transaction that has change messages for
REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT and we don't send such messages to
downstream rather they are just to update the internal state. So, we need
to skip such xacts when plugin uses the option 'skip-empty-xacts'.

Diagnosed-By: Amit Kapila
Author: Dilip Kumar
Reviewed-by: Amit Kapila
Discussion: https://postgr.es/m/CAA4eK1+OqgFNZkf7=ETe_y5ntjgDk3T0wcdkd4Sot_u1hySGfw@mail.gmail.com

This helps debuggability when looking at WAL streams containing logical
messages.

Author: Ashutosh Bapat <ashutosh.bapat@2ndquadrant.com>
Reviewed-by: Álvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://postgr.es/m/CAExHW5sWx49rKmXbg5H1Xc1t+nRv9PaYKQmgw82HPt6vWDVmDg@mail.gmail.com

Bring the signal handling for startup-packet collection into line
with the policy established in commits bedadc73 and 8e19a826,
namely don't risk running atexit callbacks when handling SIGQUIT.

Ideally, we'd not do so for SIGTERM or timeout interrupts either,
but that change seems a bit too risky for the back branches.
For now, just improve the comments in this area to describe the risk.

Also relocate where BackendInitialize re-disables these interrupts,
to minimize the code span where they're active.  This doesn't buy
a whole lot of safety, but it can't hurt.

In passing, rename startup_die() to remove confusion about whether
it is for the startup process.

Like the previous commits, back-patch to all supported branches.

Discussion: https://postgr.es/m/1850884.1599601164@sss.pgh.pa.us

Sometimes it happens that the visibility information for a tuple
becomes corrupted, either due to bugs in the database software or
external factors. Provide a function heap_force_kill() that can
be used to truncate such dead tuples to dead line pointers, and
a function heap_force_freeze() that can be used to overwrite the
visibility information in such a way that the tuple becomes
all-visible.

These functions are unsafe, in that you can easily use them to
corrupt a database that was not previously corrupted, and you can
use them to further corrupt an already-corrupted database or to
destroy data. The documentation accordingly cautions against
casual use. However, in some cases they permit recovery of data
that would otherwise be very difficult to recover, or to allow a
system to continue to function when it would otherwise be difficult
to do so.

Because we may want to add other functions for performing other
kinds of surgery in the future, the new contrib module is called
pg_surgery rather than something specific to these functions. I
proposed back-patching this so that it could be more easily used
by people running existing releases who are facing these kinds of
problems, but that proposal did not attract enough support, so
no back-patch for now.

Ashutosh Sharma, reviewed and tested by Andrey M. Borodin,
M. Beena Emerson, Masahiko Sawada, Rajkumar Raghuwanshi,
Asim Praveen, and Mark Dilger, and somewhat revised by me.

Discussion: http://postgr.es/m/CA+TgmoZW1fsU-QUNCRUQMGUygBDPVeOTLCqRdQZch=EYZnctSA@mail.gmail.com

Apparently, this was never used when
introduced (3dad73e7).

Discussion: https://www.postgresql.org/message-id/flat/511bb100-f829-ba21-2f10-9f952ec06ead%402ndquadrant.com

Add libssl and libcrypto to libpq.pc's Requires.private.  This allows
static linking to work if those libssl or libcrypto themselves have
dependencies in their *.private fields, such as -lz in some cases.
Reported-by: Sandro Mani <manisandro@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/837d1dcf-2fca-ee6e-0d7e-6bce1a1bac75@gmail.com

We have had multiple reports that point to the
'@colReorder=latn-digit' collation customization being buggy.  We have
reported this to ICU and are waiting for a fix.  In the meantime,
remove references to this from the documentation and replace it by
another reordering example.  Apparently, many users have been picking
up this example specifically from the documentation.

Author: Jehan-Guillaume de Rorthais <jgdr@dalibo.com>
Discussion: https://www.postgresql.org/message-id/flat/153201618542.1404.3611626898935613264%40wrigleys.postgresql.org

EXTRACT of date type is implemented as a wrapper around EXTRACT of
timestamp, so the code is already tested there.  But the externally
visible behavior of EXTRACT on date is not recorded anywhere.  Since
there is some discussion about reimplementing or refactoring some of
this, add some more explicit tests of EXTRACT on date, similar in
structure to existing EXTRACT tests on other data types.

Discussion: https://www.postgresql.org/message-id/flat/42b73d2d-da12-ba9f-570a-420e0cce19d9@phystech.edu

Reported-by: Robert Kahlert
Author: Daniel Gustafsson

Do some minor cleanup for commit c8434d64: 1) remove a useless
assignment (in normal builds) and 2) improve comments a little.

Back-patch to v13 where the aforementioned commit went in.

Author: Etsuro Fujita
Reviewed-by: Alvaro Herrera
Discussion: https://postgr.es/m/CAPmGK16yCd2R4=bQ4g8N2dT9TtA5ZU+qNmJ3LPc_nypbNy4_2A@mail.gmail.com

Some comments are fixed while on it.

Author: Justin Pryzby
Discussion: https://postgr.es/m/20200818171702.GK17022@telsasoft.com
Backpatch-through: 9.6

Move applicable code out of RelationBuildDesc(), which nailed relations
bypass.  Non-assert builds experienced no known problems.  Back-patch to
v13, where commit c6b92041 introduced
rd_firstRelfilenodeSubid.

Kyotaro Horiguchi.  Reported by Justin Pryzby.

Discussion: https://postgr.es/m/20200907023737.GA7158@telsasoft.com

Commit 8e19a826 changed the SIGQUIT handlers of almost all server
processes not to run atexit callbacks.  The archiver process was
skipped, perhaps because it's not connected to shared memory; but
it's just as true here that running atexit callbacks in a signal
handler is unsafe.  So let's make it work like the rest.

In HEAD and v13, we can use the common SignalHandlerForCrashExit
handler.  Before that, just tweak pgarch_exit to use _exit(2)
explicitly.

Like the previous commit, back-patch to all supported branches.

Kyotaro Horiguchi, back-patching by me

Discussion: https://postgr.es/m/1850884.1599601164@sss.pgh.pa.us

Existing callers had to take complicated detours via
DirectFunctionCall1().  This simplifies a lot of code.
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://www.postgresql.org/message-id/flat/42b73d2d-da12-ba9f-570a-420e0cce19d9@phystech.edu

Commit 15cb2bd2 neglected to make the running text match the
tables, leaving the reader with the strong impression that
we cannot count.  Also, don't drop an unrelated para between
a table and the para describing it.

Alexander Lakhin

Discussion: https://postgr.es/m/ce7debdd-c943-d7a7-9b41-687107b27831@gmail.com

Mistake in commit 68b603e1.

Reported-by: Ian Barwick

max(numeric) wasn't tested at all, min(numeric) was only used by some
unrelated tests.  Add explicit tests with the other numeric aggregate
functions.

Partitioning tuple route code assumes that the partition chosen while
descending the partition hierarchy is always the correct one.  This is
true except when the partition is the default partition and another
partition has been added concurrently: the partition constraint changes
and we don't recheck it.  This can lead to tuples mistakenly being added
to the default partition that should have been rejected.

Fix by rechecking the default partition constraint while descending the
hierarchy.

An isolation test based on the reproduction steps described by Hao Wu
(with tweaks for extra coverage) is included.

Backpatch to 12, where this bug came in with 898e5e32.

Reported by: Hao Wu <hawu@vmware.com>
Author: Amit Langote <amitlangote09@gmail.com>
Author: Álvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://postgr.es/m/CA+HiwqFqBmcSSap4sFnCBUEL_VfOMmEKaQ3gwUhyfa4c7J_-nA@mail.gmail.com
Discussion: https://postgr.es/m/DM5PR0501MB3910E97A9EDFB4C775CF3D75A42F0@DM5PR0501MB3910.namprd05.prod.outlook.com

Historically, cancel_before_shmem_exit() just silently did nothing
if the specified callback wasn't the top-of-stack.  The folly of
ignoring this case was exposed by the bugs fixed in 30364019 and
bab15004, so let's make it throw elog(ERROR) instead.

There is a decent argument to be made that PG_ENSURE_ERROR_CLEANUP
should use some separate infrastructure, so it wouldn't break if
something inside the guarded code decides to register a new
before_shmem_exit callback.  However, a survey of the surviving
uses of before_shmem_exit() and PG_ENSURE_ERROR_CLEANUP doesn't
show any plausible conflicts of that sort today, so for now we'll
forgo the extra complexity.  (It will almost certainly become
necessary if anyone ever wants to wrap PG_ENSURE_ERROR_CLEANUP
around arbitrary user-defined actions, though.)

No backpatch, since this is developer support not a production issue.

Bharath Rupireddy, per advice from Andres Freund, Robert Haas, and myself

Discussion: https://postgr.es/m/CALj2ACWk7j4F2v2fxxYfrroOF=AdFNPr1WsV+AGtHAFQOqm_pw@mail.gmail.com