It emerges that in some phases of the moon (perhaps to do with
directory entry order?), xcrun will report that the SDK path is
  /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk
which is normally a symlink to a version-numbered sibling directory.
Our heuristic to skip non-version-numbered pathnames was rejecting
that, which is the wrong thing to do.  We'd still like to end up
with a version-numbered PG_SYSROOT value, but we can have that by
dereferencing the symlink.

Like the previous fix, back-patch to all supported versions.

Discussion: https://postgr.es/m/522433.1611089678@sss.pgh.pa.us

By default VACUUM will skip pages that it can't immediately get
exclusive access to, which means that even activities as harmless
and unpredictable as checkpoint buffer writes might prevent a page
from being processed.  Ordinarily this is no big deal, but we have
a small number of test cases that examine the results of VACUUM's
processing and therefore will fail if the page of interest is skipped.
This seems to be the explanation for some rare buildfarm failures.
To fix, add the DISABLE_PAGE_SKIPPING option to the VACUUM commands
in tests where this could be an issue.

In passing, remove a duplicated query in pageinspect/sql/page.sql.

Back-patch as necessary (some of these cases are as old as v10).

Discussion: https://postgr.es/m/413923.1611006484@sss.pgh.pa.us

In commit 9eb5607e, I got the condition on checking for split or
deleted page wrong: I used && instead of ||. The comment correctly said
"concurrent split _or_ deletion".

As a result, GiST insertion could miss a concurrent split, and insert to
wrong page. Duncan Sands demonstrated this with a test script that did a
lot of concurrent inserts.

Backpatch to v12, where this was introduced. REINDEX is required to fix
indexes that were affected by this bug.

Backpatch-through: 12
Reported-by: Duncan Sands
Discussion: https://www.postgresql.org/message-id/a9690483-6c6c-3c82-c8ba-dc1a40848f11%40deepbluecap.com

Since commit f0f13a3a, we estimate
ModifyTable paths without a RETURNING clause differently.  Update an
example from the manual that showed the old behavior.

Author: Takayuki Tsunakawa <tsunakawa.takay@fujitsu.com>
Reviewed-by: Laurenz Albe <laurenz.albe@cybertec.at>
Discussion: https://postgr.es/m/TYAPR01MB29905674F41693BBA9DA28CAFEA20%40TYAPR01MB2990.jpnprd01.prod.outlook.com

DROP OWNED BY has a specific code path to remove ACLs stored in
pg_default_acl when cleaning up shared dependencies that had no
coverage with the existing tests.  This issue has been found while
digging into the bug fixed by 21378e1f.

As ALTER DEFAULT PRIVILEGES impacts the ACLs of all objects created
while the default permissions are visible, the test uses a transaction
rollback to isolate the test and avoid any impact with other sessions
running in parallel.

Reviewed-by: Álvaro Herrera
Discussion: https://postgr.es/m/YAbQ1OD+3ip4lRv8@paquier.xyz

Specifying duplicated objects in this command would lead to unique
constraint violations in pg_default_acl or "tuple already updated by
self" errors.  Similarly to GRANT/REVOKE, increment the command ID after
each subcommand processing to allow this case to work transparently.

A regression test is added by tweaking one of the existing queries of
privileges.sql to stress this case.

Reported-by: Andrus
Author: Michael Paquier
Reviewed-by: Álvaro Herrera
Discussion: https://postgr.es/m/ae2a7dc1-9d71-8cba-3bb9-e4cb7eb1f44e@hot.ee
Backpatch-through: 9.5

Somebody extended search_plan_tree() to treat MergeAppend exactly
like Append, which is 100% wrong, because unlike Append we can't
assume that only one input node is actively returning tuples.
Hence a cursor using a MergeAppend across a UNION ALL or inheritance
tree could falsely match a WHERE CURRENT OF query at a row that
isn't actually the cursor's current output row, but coincidentally
has the same TID (in a different table) as the current output row.

Delete the faulty code; this means that such a case will now return
an error like 'cursor "foo" is not a simply updatable scan of table
"bar"', instead of silently misbehaving.  Users should not find that
surprising though, as the same cursor query could have failed that way
already depending on the chosen plan.  (It would fail like that if the
sort were done with an explicit Sort node instead of MergeAppend.)

Expand the clearly-inadequate commentary to be more explicit about
what this code is doing, in hopes of forestalling future mistakes.

It's been like this for awhile, so back-patch to all supported
branches.

Discussion: https://postgr.es/m/482865.1611075182@sss.pgh.pa.us

Block numbers are 32-bit unsigned integers.  Therefore, the smallest
SQL integer type that they can fit in is bigint.  However, in the
pageinspect module, most input and output parameters dealing with
block numbers were declared as int.  The behavior with block numbers
larger than a signed 32-bit integer was therefore dubious.  Change
these arguments to type bigint and add some more explicit error
checking on the block range.

(Other contrib modules appear to do this correctly already.)

Since we are changing argument types of existing functions, in order
to not misbehave if the binary is updated before the extension is
updated, we need to create new C symbols for the entry points, similar
to how it's done in other extensions as well.
Reported-by: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Reviewed-by: Alvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://www.postgresql.org/message-id/flat/d8f6bdd536df403b9b33816e9f7e0b9d@G08CNEXMBPEKD05.g08.fujitsu.local

Previously the document didn't mention the case where
postgres_fdw_get_connections() returns NULL in server_name column.
Users might be confused about why NULL was returned.

This commit adds the note that, in postgres_fdw_get_connections(),
the server name of an invalid connection will be NULL if the server is dropped.

Suggested-by: Zhijie Hou
Author: Bharath Rupireddy
Reviewed-by: Zhijie Hou, Fujii Masao
Discussion: https://postgr.es/m/e7ddd14e96444fce88e47a709c196537@G08CNEXMBPEKD05.g08.fujitsu.local

This is a leftover from commit 0926e96c. Changing this separately
because this file is being modified for upcoming patch logical replication
of 2PC.

Author: Peter Smith
Discussion: https://postgr.es/m/CAHut+Ps+EgG8KzcmAyAgBUi_vuTps6o9ZA8DG6SdnO0-YuOhPQ@mail.gmail.com

Backpatch-through: 10

execCurrent.c's search_plan_tree() assumed that ForeignScanStates
and CustomScanStates necessarily have a valid ss_currentRelation.
This is demonstrably untrue for postgres_fdw's remote join and
remote aggregation plans, and non-leaf custom scans might not have
an identifiable scan relation either.  Avoid crashing by ignoring
such nodes when the field is null.

This solution will lead to errors like 'cursor "foo" is not a
simply updatable scan of table "bar"' in cases where maybe we
could have allowed WHERE CURRENT OF to work.  That's not an issue
for postgres_fdw's usages, since joins or aggregations would render
WHERE CURRENT OF invalid anyway.  But an otherwise-transparent
upper level custom scan node might find this annoying.  When and if
someone cares to expend work on such a scenario, we could invent a
custom-scan-provider callback to determine what's safe.

Report and patch by David Geier, commentary by me.  It's been like
this for awhile, so back-patch to all supported branches.

Discussion: https://postgr.es/m/0253344d-9bdd-11c4-7f0d-d88c02cd7991@swarm64.com

This is better style and more symmetrical with the other if-branch.
This likely should have been included in 9de77b54 (which created
the opportunity), but it was overlooked.

Japin Li

Discussion: https://postgr.es/m/MEYP282MB16699FA4A7CD57EB250E871FB6A40@MEYP282MB1669.AUSP282.PROD.OUTLOOK.COM

We had bytea btrim() already, but for some reason not the other two.

Joel Jacobson

Discussion: https://postgr.es/m/d10cd5cd-a901-42f1-b832-763ac6f7ff3a@www.fastmail.com

Previously, the per-barrier-type functions tasked with absorbing
them were expected to always succeed and never throw an error.
However, that's a bit inconvenient. Further study has revealed that
there are realistic cases where it might not be possible to absorb
a ProcSignalBarrier without terminating the transaction, or even
the whole backend. Similarly, for some barrier types, there might
be other reasons where it's not reasonably possible to absorb the
barrier at certain points in the code, so provide a way for a
per-barrier-type function to reject absorbing the barrier.

Unfortunately, there's still no committed code making use of this
infrastructure; hopefully, we'll get there. :-(

Patch by me, reviewed by Andres Freund and Amul Sul.

Discussion: http://postgr.es/m/20200908182005.xya7wetdh3pndzim@alap3.anarazel.de
Discussion: http://postgr.es/m/CA+Tgmob56Pk1-5aTJdVPCWFHon7me4M96ENpGe9n_R4JUjjhZA@mail.gmail.com

This was missed in 960869da

Reported-By: Laurenz Albe
Discussion: https://postgr.es/m/4f0aacc5fe1b4bfafa32b36ecd97469fae526a75.camel@cybertec.at

Per Coverity. BuildIndexValueDescription() cannot actually return NULL in
this instance, because it only returns NULL if the user doesn't have the
required privileges, and this function can only be used by superuser. But
better safe than sorry.

When certain parameters are changed on a physical replication primary,
this is communicated to standbys using the XLOG_PARAMETER_CHANGE WAL
record.  The standby then checks whether its own settings are at least
as big as the ones on the primary.  If not, the standby shuts down
with a fatal error.

This patch changes this behavior for hot standbys to pause recovery at
that point instead.  That allows read traffic on the standby to
continue while database administrators figure out next steps.  When
recovery is unpaused, the server shuts down (as before).  The idea is
to fix the parameters while recovery is paused and then restart when
there is a maintenance window.
Reviewed-by: Sergei Kornilov <sk@zsrv.org>
Discussion: https://www.postgresql.org/message-id/flat/4ad69a4c-cc9b-0dfe-0352-8b1b0cd36c7b@2ndquadrant.com

This commit adds function postgres_fdw_get_connections() to return
the foreign server names of all the open connections that postgres_fdw
established from the local session to the foreign servers. This function
also returns whether each connection is valid or not.

This function is useful when checking all the open foreign server connections.
If we found some connection to drop, from the result of function, probably
we can explicitly close them by the function that upcoming commit will add.

This commit bumps the version of postgres_fdw to 1.1 since it adds
new function.

Author: Bharath Rupireddy, tweaked by Fujii Masao
Reviewed-by: Zhijie Hou, Alexey Kondratov, Zhihong Yu, Fujii Masao
Discussion: https://postgr.es/m/2d5cb0b3-a6e8-9bbb-953f-879f47128faa@oss.nttdata.com

This continues the work done in b5913f61.  All the options of those
commands are changed to use hex values rather than enums to reduce the
risk of compatibility bugs when introducing new options.  Each option
set is moved into a new structure that can be extended with more
non-boolean options (this was already the case of VACUUM).  The code of
REINDEX is restructured so as manual REINDEX commands go through a
single routine from utility.c, like VACUUM, to ease the allocation
handling of option parameters when a command needs to go through
multiple transactions.

This can be used as a base infrastructure for future patches related to
those commands, including reindex filtering and tablespace support.

Per discussion with people mentioned below, as well as Alvaro Herrera
and Peter Eisentraut.

Author: Michael Paquier, Justin Pryzby
Reviewed-by: Alexey Kondratov, Justin Pryzby
Discussion: https://postgr.es/m/X8riynBLwxAD9uKk@paquier.xyz

The gist_page_items() function opened the index relation on first call and
closed it on the last call. But there's no guarantee that the function is
run to completion, leading to a relcache leak and warning at the end of
the transaction. To fix, refactor the function to return all the rows in
one call, as a tuplestore.

Reported-by: Tom Lane
Discussion: https://www.postgresql.org/message-id/234863.1610916631%40sss.pgh.pa.us

Make sure COPY FREEZE marks the pages as PD_ALL_VISIBLE and updates the
visibility map. Until now we only marked individual tuples as frozen,
but page-level flags were not updated, so the first VACUUM after the
COPY FREEZE had to rewrite the whole table.

This is a fairly old patch, and multiple people worked on it. The first
version was written by Jeff Janes, and then reworked by Pavan Deolasee
and Anastasia Lubennikova.

Author: Anastasia Lubennikova, Pavan Deolasee, Jeff Janes
Reviewed-by: Kuntal Ghosh, Jeff Janes, Tomas Vondra, Masahiko Sawada,
             Andres Freund, Ibrar Ahmed, Robert Haas, Tatsuro Ishii,
             Darafei Praliaskouski
Discussion: https://postgr.es/m/CABOikdN-ptGv0mZntrK2Q8OtfUuAjqaYMGmkdU1dCKFtUxVLrg@mail.gmail.com
Discussion: https://postgr.es/m/CAMkU%3D1w3osJJ2FneELhhNRLxfZitDgp9FPHee08NT2FQFmz_pQ%40mail.gmail.com

The stanza to report a "partial" match could overrun the initially
allocated output array, so it needs its own copy of the array-resizing
logic that's in the main loop.  I overlooked the need for this in
ca8217c1.

Per report from Alexander Lakhin.

Discussion: https://postgr.es/m/3206aace-50db-e02a-bbea-76d5cdaa2cb6@gmail.com

Data checksums did not have a longer discussion in the docs,
this adds a short section with an overview.

Extracted from the larger patch for on-line enabling of checksums, which
has many more authors and reviewers.

Author: Daniel Gustafsson
Reviewed-By: Magnus Hagander, Michael Banck (and others through the big patch)
Discussion: https://postgr.es/m/5ff49fa4.1c69fb81.658f3.04ac@mx.google.com

Reverts 891a1d0b, because the new  psql command \dX only worked for
users users who can read pg_statistic_ext_data catalog, and most regular
users lack that privilege (the catalog may contain sensitive user data).

Reported-by: Noriyoshi Shinoda
Discussion: https://postgr.es/m/c027a541-5856-75a5-0868-341301e1624b%40nttcom.co.jp_1

Specifying this parameter removes the informational messages about how
to start the server. This is intended for use by wrappers in different
packaging systems, where those instructions would most likely be wrong
anyway, but the other output from initdb would still be useful (and thus
just redirecting everything to /dev/null would be bad).

Author: Magnus Hagander
Reviewed-By: Peter Eisentraut
Discusion: https://postgr.es/m/CABUevEzo4t5bmTXF0_B9WzmuWpVbMpkNZZiGvzV8NZa-=fPqeQ@mail.gmail.com

This add counters for number of sessions, the different kind of session
termination types, and timers for how much time is spent in active vs
idle in a database to pg_stat_database.

Internally this also renames the parameter "force" to disconnect. This
was the only use-case for the parameter before, so repurposing it to
this mroe narrow usecase makes things cleaner than inventing something
new.

Author: Laurenz Albe
Reviewed-By: Magnus Hagander, Soumyadeep Chakraborty, Masahiro Ikeda
Discussion: https://postgr.es/m/b07e1f9953701b90c66ed368656f2aef40cac4fb.camel@cybertec.at

The new command lists extended statistics objects, possibly with their
sizes. All past releases with extended statistics are supported.

Author: Tatsuro Yamada
Reviewed-by: Julien Rouhaud, Alvaro Herrera, Tomas Vondra
Discussion: https://postgr.es/m/c027a541-5856-75a5-0868-341301e1624b%40nttcom.co.jp_1

There is no CopyResponse message; it should be CopyOutResponse.

Also, if there is no WAL to stream, the server does not immediately
send a CommandComplete; it's a historical timeline, so it will send a
response tuple first.

Discussion: https://postgr.es/m/0a2c985ebcaa1acd385350aeba561b6509187394.camel@j-davis.com

The context is an object that no longer bears some aclitem that it bore
initially.  (A user issued REVOKE or GRANT statements upon the object.)
pg_dump is forming SQL to reproduce the object ACL.  Since initdb
creates no ACL bearing GRANT OPTION, reaching this bug requires an
extension where the creation script establishes such an ACL.  No PGXN
extension does that.  If an installation did reach the bug, pg_dump
would have omitted a semicolon, causing a REVOKE and the next SQL
statement to fail.  Separately, since the affected code exists to
eliminate an entire aclitem, it wants plain REVOKE, not REVOKE GRANT
OPTION FOR.  Back-patch to 9.6, where commit
23f34fa4 first appeared.

Discussion: https://postgr.es/m/20210109102423.GA160022@rfd.leadboat.com

Every core SLRU wraps around.  With the exception of pg_notify, the wrap
point can fall in the middle of a page.  Account for this in the
PagePrecedes callback specification and in SimpleLruTruncate()'s use of
said callback.  Update each callback implementation to fit the new
specification.  This changes SerialPagePrecedesLogically() from the
style of asyncQueuePagePrecedes() to the style of CLOGPagePrecedes().
(Whereas pg_clog and pg_serial share a key space, pg_serial is nothing
like pg_notify.)  The bug fixed here has the same symptoms and user
followup steps as 592a589a04bd456410b853d86bd05faa9432cbbb.  Back-patch
to 9.5 (all supported versions).

Reviewed by Andrey Borodin and (in earlier versions) by Tom Lane.

Discussion: https://postgr.es/m/20190202083822.GC32531@gust.leadboat.com

The result of TextDatumGetCString is already palloc'ed so we don't need to
allocate memory for it again. We decide not to backpatch it as there
doesn't seem to be any case where it can create a meaningful leak.

Author: Zhijie Hou
Reviewed-by: Daniel Gustafsson
Discussion: https://postgr.es/m/229fed2eb8c54c71a96ccb99e516eb12@G08CNEXMBPEKD05.g08.fujitsu.local

Add a check that CREATE STATISTICS does not add extended statistics on
system catalogs, similarly to indexes etc.  It can be overriden using
the allow_system_table_mods GUC.

This bug exists since 7b504eb2, adding the extended statistics, so
backpatch all the way back to PostgreSQL 10.

Author: Tomas Vondra
Reported-by: Dean Rasheed
Backpatch-through: 10
Discussion: https://postgr.es/m/CAEZATCXAPrrOKwEsyZKQ4uzzJQWBCt6QAvOcgqRGdWwT1zb%2BrQ%40mail.gmail.com

In cases where Xcode is newer than the underlying macOS version,
asking xcodebuild for the SDK path will produce a pointer to the
SDK shipped with Xcode, which may end up building code that does
not work on the underlying macOS version.  It appears that in
such cases, xcodebuild's answer also fails to match the default
behavior of Apple's compiler: assuming one has installed Xcode's
"command line tools", there will be an SDK for the OS's own version
in /Library/Developer/CommandLineTools, and the compiler will
default to using that.  This is all pretty poorly documented,
but experimentation suggests that "xcrun --show-sdk-path" gives
the sysroot path that the compiler is actually using, at least
in some cases.  Hence, try that first, but revert to xcodebuild
if xcrun fails (in very old Xcode, it is missing or lacks the
--show-sdk-path switch).

Also, "xcrun --show-sdk-path" may give a path that is valid but lacks
any OS version identifier.  We don't really want that, since most
of the motivation for wiring -isysroot into the build flags at all
is to ensure that all parts of a PG installation are built against
the same SDK, even when considering extensions built later and/or on
a different machine.  Insist on finding "N.N" in the directory name
before accepting the result.  (Adding "--sdk macosx" to the xcrun
call seems to produce the same answer as xcodebuild, but usually
more quickly because it's cached, so we also try that as a fallback.)

The core reason why we don't want to use Xcode's default SDK in cases
like this is that Apple's technology for introducing new syscalls
does not play nice with Autoconf: for example, configure will think
that preadv/pwritev exist when using a Big Sur SDK, even when building
on an older macOS version where they don't exist.  It'd be nice to
have a better solution to that problem, but this patch doesn't attempt
to fix that.

Per report from Sergey Shinderuk.  Back-patch to all supported versions.

Discussion: https://postgr.es/m/ed3b8e5d-0da8-6ebd-fd1c-e0ac80a4b204@postgrespro.ru

This is like commit c98763bf, but for REINDEX CONCURRENTLY.  To wit:
this flags indicates that the current process is safe to ignore for the
purposes of waiting for other snapshots, when doing CREATE INDEX
CONCURRENTLY and REINDEX CONCURRENTLY.  This helps two processes doing
either of those things not deadlock, and also avoids spurious waits.

Author: Álvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Dmitry Dolgov <9erthalion6@gmail.com>
Reviewed-by: Hamid Akhtar <hamid.akhtar@gmail.com>
Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Discussion: https://postgr.es/m/20201130195439.GA24598@alvherre.pgsql

Commit ac883ac4 refactored shm_toc_estimate() but changed its calculation
of shared memory size for TOC incorrectly. Previously this could cause too
large memory to be allocated.

Back-patch to v11 where the bug was introduced.

Author: Takayuki Tsunakawa
Discussion: https://postgr.es/m/TYAPR01MB2990BFB73170E2C4921E2C4DFEA80@TYAPR01MB2990.jpnprd01.prod.outlook.com

The last reference to those variables has been removed in aef8948f, so
this cleans up a bit the code.

Discussion: https://postgr.es/m/X//ggAqmTtt+3t7X@paquier.xyz

The counter tracking the last segment number recycled was getting
initialized when recycling one single segment, while it should be used
across a full cycle of segments recycled to prevent useless checks
related to entries already recycled.

This performance issue has been introduced by b2a5545b, and it was first
implemented in 61b86142.

No backpatch is done per the lack of field complaints.

Reported-by: Andres Freund, Thomas Munro
Author: Michael Paquier
Reviewed-By: Andres Freund
Discussion: https://postgr.es/m/20170621211016.eln6cxxp3jrv7m4m@alap3.anarazel.de
Discussion: https://postgr.es/m/CA+hUKG+DRiF9z1_MU4fWq+RfJMxP7zjoptfcmuCFPeO4JM2iVg@mail.gmail.com

The foreign server OID stored in the connection cache entry is used as
a lookup key to directly get the server name.

Previously since the connection cache entry did not have the server OID,
postgres_fdw had to get the server OID at first from user mapping before
getting the server name. So if the corresponding user mapping was dropped,
postgres_fdw could raise the error "cache lookup failed for user mapping"
while looking up user mapping and fail to get the server name even though
the server had not been dropped yet.

Author: Bharath Rupireddy
Reviewed-by: Fujii Masao
Discussion: https://postgr.es/m/CALj2ACVRZPUB7ZwqLn-6DY8C_UmPs6084gSpHA92YBv++1AJXA@mail.gmail.com

This is the same fix as commit 9eabfe30 applied to INDEX ATTACH
entries, but for table-to-publication attachments.  As in that
case, even though the backend doesn't record "ownership" of the
attachment, we still ought to label it in the dump archive with
the role name that should run the ALTER PUBLICATION command.
The existing behavior causes the ALTER to be done by the original
role that started the restore; that will usually work fine, but
there may be corner cases where it fails.

The bulk of the patch is concerned with changing struct
PublicationRelInfo to include a pointer to the associated
PublicationInfo object, so that we can get the owner's name
out of that when the time comes.  While at it, I rewrote
getPublicationTables() to do just one query of pg_publication_rel,
not one per table.

Back-patch to v10 where this code was introduced.

Discussion: https://postgr.es/m/1165710.1610473242@sss.pgh.pa.us