Remove various unused parameters in pg_dump code.  These have all
become unused over time or were never used.

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

Commit be0a6666 left behind a comment about the order of some tests that
didn't make sense without the expensive division, and in fact we might
as well change the order to one that fails more cheaply most of the time
as a micro-optimization.  Also, remove the "+ 1" applied to max_bucket,
to drop an instruction and match the original behavior.  Per review
from Tom Lane.

Discussion: https://postgr.es/m/VI1PR0701MB696044FC35013A96FECC7AC8F62D0%40VI1PR0701MB6960.eurprd07.prod.outlook.com

Since ancient times we have had support for a fill factor (maximum load
factor) to be set for a dynahash hash table, but:

1.  It was an integer, whereas for in-memory hash tables interesting
load factor targets are probably somewhere near the 0.75-1.0 range.

2.  It was implemented in a way that performed an expensive division
operation that regularly showed up in profiles.

3.  We are not aware of anyone ever having used a non-default value.

Therefore, remove support, effectively fixing it at 1.

Author: Jakub Wartak <Jakub.Wartak@tomtom.com>
Reviewed-by: Alvaro Herrera <alvherre@2ndquadrant.com>
Reviewed-by: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Reviewed-by: Thomas Munro <thomas.munro@gmail.com>
Reviewed-by: David Rowley <dgrowleyml@gmail.com>
Discussion: https://postgr.es/m/VI1PR0701MB696044FC35013A96FECC7AC8F62D0%40VI1PR0701MB6960.eurprd07.prod.outlook.com

Up to now, if you tried to omit "AS" before a column label in a SELECT
list, it would only work if the column label was an IDENT, that is not
any known keyword.  This is rather unfriendly considering that we have
so many keywords and are constantly growing more.  In the wake of commit
1ed6b895 it's possible to improve matters quite a bit.

We'd originally tried to make this work by having some of the existing
keyword categories be allowed without AS, but that didn't work too well,
because each category contains a few special cases that don't work
without AS.  Instead, invent an entirely orthogonal keyword property
"can be bare column label", and mark all keywords that way for which
we don't get shift/reduce errors by doing so.

It turns out that of our 450 current keywords, all but 39 can be made
bare column labels, improving the situation by over 90%.  This number
might move around a little depending on future grammar work, but it's
a pretty nice improvement.

Mark Dilger, based on work by myself and Robert Haas;
review by John Naylor

Discussion: https://postgr.es/m/38ca86db-42ab-9b48-2902-337a0d6b8311@2ndquadrant.com

According to buildfarm member sungazer, the behavior of VACUUM can be
unstable in these tests even if we prevent autovacuum from running on
the tables in question, apparently because even a manual vacuum can
behave differently depending on whether anything else is running that
holds back the global xmin. So use a temporary table instead, which
as of commit a7212be8 enables
vacuuming using a more aggressive cutoff.

This approach can't be used for the regression test that involves a
materialized view, but that test doesn't run vacuum, so it shouldn't
be prone to this particular failure mode.

Analysis by Tom Lane. Patch by Ashutosh Sharma and me.

Discussion: http://postgr.es/m/665524.1599948007@sss.pgh.pa.us

Author: Amit Langote
Reviewed-by: Amit Kapila
Discussion: https://postgr.es/m/CA+HiwqE20oZoix13JyCeALpTf_SmjarZWtBFe5sND6zz+iupAw@mail.gmail.com

After commits 85f6b49c and 3ba59ccc, we can allow parallel inserts
which was earlier not possible as parallel group members won't conflict
for relation extension and page lock.  In those commits, we forgot to
update comments at few places.

Author: Amit Kapila
Reviewed-by: Robert Haas and Dilip Kumar
Backpatch-through: 13
Discussion: https://postgr.es/m/CAFiTN-tMrQh5FFMPx5aWJ+1gi1H6JxktEhq5mDwCHgnEO5oBkA@mail.gmail.com

It's not quite clear why commit 45b98057 has resulted in
some instability here, though interference from concurrent
autovacuum runs seems like a reasonable guess.  What is
clear is that the output ordering of the test queries is
underdetermined for no very good reason.  Extend the
ORDER BY keys in hopes of fixing the buildfarm.

Discussion: https://postgr.es/m/147499.1600351924@sss.pgh.pa.us

This feature has been a thorn in our sides for a long time, causing
many grammatical ambiguity problems.  It doesn't seem worth the
pain to continue to support it, so remove it.

There are some follow-on improvements we can make in the grammar,
but this commit only removes the bare minimum number of productions,
plus assorted backend support code.

Note that pg_dump and psql continue to have full support, since
they may be used against older servers.  However, pg_dump warns
about postfix operators.  There is also a check in pg_upgrade.

Documentation-wise, I (tgl) largely removed the "left unary"
terminology in favor of saying "prefix operator", which is
a more standard and IMO less confusing term.

I included a catversion bump, although no initial catalog data
changes here, to mark the boundary at which oprkind = 'r'
stopped being valid in pg_operator.

Mark Dilger, based on work by myself and Robert Haas;
review by John Naylor

Discussion: https://postgr.es/m/38ca86db-42ab-9b48-2902-337a0d6b8311@2ndquadrant.com

The "!" operator is our only built-in postfix operator.  Remove it,
on the way to removal of grammar support for postfix operators.

There is also a "!!" prefix operator, but since it's been marked
deprecated for most of its existence, we might as well remove it too.

Also zap the SQL alias function numeric_fac(), which seems to have
equally little reason to live.

Mark Dilger, based on work by myself and Robert Haas;
review by John Naylor

Discussion: https://postgr.es/m/38ca86db-42ab-9b48-2902-337a0d6b8311@2ndquadrant.com

I despair of people keeping the README file's notes in sync with
the actual exclusion list, so move the notes into the exclusion file.
Adjust the pgindent script to explicitly ignore comments in the file,
just in case (though it's hard to believe any would match filenames).

Extend the list so that it doesn't process any files we'd not wish it to
even in a fully-built-out development directory.  (There are still a
couple of derived files that it wants to reformat, but fixing the
generator scripts for those seems like fit material for a separate patch.)

Discussion: https://postgr.es/m/79ed5348-be7a-b647-dd40-742207186a22@2ndquadrant.com

Instead of hard-wiring specific verbosity levels into the option
processing of client applications, invent pg_logging_increase_verbosity()
and encourage clients to implement --verbose by calling that.  Then,
the common convention that more -v's gets you more verbosity just works.

In particular, this allows resurrection of the debug-grade messages that
have long existed in pg_dump and its siblings.  They were unreachable
before this commit due to lack of a way to select PG_LOG_DEBUG logging
level.  (It appears that they may have been unreachable for some time
before common/logging.c was introduced, too, so I'm not specifically
blaming cc8d4151 for the oversight.  One reason for thinking that is
that it's now apparent that _allocAH()'s message needs a null-pointer
guard.  Testing might have failed to reveal that before 96bf88d5.)

Discussion: https://postgr.es/m/1173106.1600116625@sss.pgh.pa.us

For parallel btree scan to work for array of scan keys, it should reach
BTPARALLEL_DONE state once for every distinct combination of array keys.
This is required to ensure that the parallel workers don't try to seize
blocks at the same time for different scan keys. We missed to update this
state when we discovered that the scan keys can't be satisfied.

Author: James Hunter
Reviewed-by: Amit Kapila
Tested-by: Justin Pryzby
Backpatch-through: 10, where it was introduced
Discussion: https://postgr.es/m/4248CABC-25E3-4809-B4D0-128E1BAABC3C@amazon.com

In the particular case of GRANTED BY, this is specified in the SQL
standard.  Since in PostgreSQL, CURRENT_ROLE is equivalent to
CURRENT_USER, and CURRENT_USER is already supported here, adding
CURRENT_ROLE is trivial.  The other cases are PostgreSQL extensions,
but for the same reason it also makes sense there.
Reviewed-by: Vik Fearing <vik@postgresfriends.org>
Reviewed-by: Asif Rehman <asifr.rehman@gmail.com>
Reviewed-by: Alvaro Herrera <alvherre@2ndquadrant.com>
Discussion: https://www.postgresql.org/message-id/flat/f2feac44-b4c5-f38f-3699-2851d6a76dc9%402ndquadrant.com

This adds a new optional support function to the GiST access method:
sortsupport. If it is defined, the GiST index is built by sorting all data
to the order defined by the sortsupport's comparator function, and packing
the tuples in that order to GiST pages. This is similar to how B-tree
index build works, and is much faster than inserting the tuples one by
one. The resulting index is smaller too, because the pages are packed more
tightly, upto 'fillfactor'. The normal build method works by splitting
pages, which tends to lead to more wasted space.

The quality of the resulting index depends on how good the opclass-defined
sort order is. A good order preserves locality of the input data.

As the first user of this facility, add 'sortsupport' function to the
point_ops opclass. It sorts the points in Z-order (aka Morton Code), by
interleaving the bits of the X and Y coordinates.

Author: Andrey Borodin
Reviewed-by: Pavel Borisov, Thomas Munro
Discussion: https://www.postgresql.org/message-id/1A36620E-CAD8-4267-9067-FB31385E7C0D%40yandex-team.ru

OpenSSL was quoted in inconsistent ways in many places of the docs,
sometimes with <application>, <productname> or just nothing.

Author: Daniel Gustafsson
Discussion: https://postgr.es/m/DA91E5F0-5F9D-41A7-A7A6-B91CDE0F1D63@yesql.se

It is not possible to get a list of foreign schemas as the server is not
known, so this provides instead a list of local schemas, which is more
useful than nothing if using a loopback server or having schema names
matching in the local and remote servers.

Author: Jeff Janes
Reviewed-by: Tom Lane, Michael Paquier
Discussion: https://postgr.es/m/CAMkU=1wr7Roj41q-XiJs=Uyc2xCmHhcGGy7J-peJQK-e+w=ghw@mail.gmail.com

Because the code path taken for SQL commands executed in a walsender
will update the process title, we pretty much have to update the
title for replication commands as well.  Otherwise, the title shows
"idle" for the rest of a logical walsender's lifetime once it's
executed any SQL command.

Playing with this, I confirm that a walsender now typically spends
most of its life reporting
	walsender postgres [local] START_REPLICATION
Considering this in isolation, it might be better to have it say
	walsender postgres [local] sending replication data
However, consistency with the other cases seems to be a stronger
argument.

In passing, remove duplicative pgstat_report_activity call.

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

Adjust the whitespace in the emitted files so that it matches
what pgindent would do.  This makes the generated files look
like they match project style, and avoids confusion if someone
does run pgindent on the generated files.

Also, add probes.h to pgindent's exclusion list, because it can
confuse pgindent, plus there's not much point in processing it.

Daniel Gustafsson, additional fixes by me

Discussion: https://postgr.es/m/79ed5348-be7a-b647-dd40-742207186a22@2ndquadrant.com

Since commit fd5942c1 (2012, 9.3-era), walsender has been sending
completion tags for certain replication commands twice -- and they're
not even consistent.  Apparently neither libpq nor JDBC have a problem
with it, but it's not kosher.  Fix by remove the EndCommand() call in
the common code path for them all, and inserting specific calls to
EndReplicationCommand() specifically in those places where it's needed.

EndReplicationCommand() is a new simple function to send the completion
tag for replication commands.  Do this instead of sending a generic
SELECT completion tag for them all, which was also pretty bogus (if
innocuous).  While at it, change StartReplication() to use
EndReplicationCommand() instead of pg_puttextmessage().

In commit 2f966131, I failed to realize that replication commands
are not close-enough kin of regular SQL commands, so the
DROP_REPLICATION_SLOT tag I added is undeserved and a type pun.  Take it
out.

Backpatch to 13, where the latter commit appeared.  The duplicate tag
has been sent since 9.3, but since nothing is broken, it doesn't seem
worth fixing.

Per complaints from Tom Lane.

Discussion: https://postgr.es/m/1347966.1600195735@sss.pgh.pa.us

We decided that the policy established in commit 7634bd4f for
the bgwriter, checkpointer, walwriter, and walreceiver processes,
namely that they should accept SIGQUIT at all times, really ought
to apply uniformly to all postmaster children.  Therefore, get
rid of the duplicative and inconsistent per-process code for
establishing that signal handler and removing SIGQUIT from BlockSig.
Instead, make InitPostmasterChild do it.

The handler set up by InitPostmasterChild is SignalHandlerForCrashExit,
which just summarily does _exit(2).  In interactive backends, we
almost immediately replace that with quickdie, since we would prefer
to try to tell the client that we're dying.  However, this patch is
changing the behavior of autovacuum (both launcher and workers), as
well as walsenders.  Those processes formerly also used quickdie,
but AFAICS that was just mindless copy-and-paste: they don't have
any interactive client that's likely to benefit from being told this.

The stats collector continues to be an outlier, in that it thinks
SIGQUIT means normal exit.  That should probably be changed for
consistency, but there's another patch set where that's being
dealt with, so I didn't do so here.

Discussion: https://postgr.es/m/644875.1599933441@sss.pgh.pa.us

Since there is only one place that actually needs the partition check
expression, namely ExecPartitionCheck, it's better to fetch it from
the relcache there.  In this way we will never fetch it at all if
the query never has use for it, and we still fetch it just once when
we do need it.

The reason for taking an interest in this is that if the relcache
doesn't already have the check expression cached, fetching it
requires obtaining AccessShareLock on the partition root.  That
means that operations that look like they should only touch the
partition itself will also take a lock on the root.  In particular
we observed that TRUNCATE on a partition may take a lock on the
partition's root, contributing to a deadlock situation in parallel
pg_restore.

As written, this patch does have a small cost, which is that we
are microscopically reducing efficiency for the case where a partition
has an empty check expression.  ExecPartitionCheck will be called,
and will go through the motions of setting up and checking an empty
qual, where before it would not have been called at all.  We could
avoid that by adding a separate boolean flag to track whether there
is a partition expression to test.  However, this case only arises
for a default partition with no siblings, which surely is not an
interesting case in practice.  Hence adding complexity for it
does not seem like a good trade-off.

Amit Langote, per a suggestion by me

Discussion: https://postgr.es/m/VI1PR03MB31670CA1BD9625C3A8C5DD05EB230@VI1PR03MB3167.eurprd03.prod.outlook.com

Commit d114cc53 overlooked the fact that pg_upgrade'd B-Tree indexes
have leaf page high keys whose offset numbers do not match the one from
the copy of the tuple one level up (the copy stored with a downlink for
leaf page's right sibling page).  This led to false positive reports of
corruption from bt_index_parent_check() when it was called to verify a
pg_upgrade'd index.

To fix, skip comparing the offset number on pg_upgrade'd B-Tree indexes.

Author: Anastasia Lubennikova <a.lubennikova@postgrespro.ru>
Author: Peter Geoghegan <pg@bowt.ie>
Reported-By: Andrew Bille <andrewbille@gmail.com>
Diagnosed-By: Anastasia Lubennikova <a.lubennikova@postgrespro.ru>
Bug: #16619
Discussion: https://postgr.es/m/16619-aaba10f83fdc1c3c@postgresql.org
Backpatch: 13-, where child check was enhanced.

If a partitioned table's column is already marked NOT NULL, there is
no need to examine its partitions, because we can rely on previous
DDL to have enforced that the child columns are NOT NULL as well.
(Unfortunately, the same cannot be said for traditional inheritance,
so for now we have to restrict the optimization to partitioned tables.)
Hence, we may skip recursing to child tables in this situation.

The reason this case is worth worrying about is that when pg_dump dumps
a partitioned table having a primary key, it will include the requisite
NOT NULL markings in the CREATE TABLE commands, and then add the
primary key as a separate step.  The primary key addition generates a
SET NOT NULL as a subcommand, just to be sure.  So the situation where
a SET NOT NULL is redundant does arise in the real world.

Skipping the recursion does more than just save a few cycles: it means
that a command such as "ALTER TABLE ONLY partition_parent ADD PRIMARY
KEY" will take locks only on the partition parent table, not on the
partitions.  It turns out that parallel pg_restore is effectively
assuming that that's true, and has little choice but to do so because
the dependencies listed for such a TOC entry don't include the
partitions.  pg_restore could thus issue this ALTER while data restores
on the partitions are still in progress.  Taking unnecessary locks on
the partitions not only hurts concurrency, but can lead to actual
deadlock failures, as reported by Domagoj Smoljanovic.

(A contributing factor in the deadlock is that TRUNCATE on a child
partition wants a non-exclusive lock on the parent.  This seems
likewise unnecessary, but the fix for it is more invasive so we
won't consider back-patching it.  Fortunately, getting rid of one
of these two poor behaviors is enough to remove the deadlock.)

Although support for partitioned primary keys came in with v11,
this patch is dependent on the SET NOT NULL refactoring done by
commit f4a3fdfb, so we can only patch back to v12.

Patch by me; thanks to Alvaro Herrera and Amit Langote for review.

Discussion: https://postgr.es/m/VI1PR03MB31670CA1BD9625C3A8C5DD05EB230@VI1PR03MB3167.eurprd03.prod.outlook.com

The code recorded cache invalidation events by zeroing the "localreloid"
field of affected cache entries.  However, it's possible for an inval
event to occur even while we have the entry open and locked.  So an
ill-timed inval could result in "cache lookup failed for relation 0"
errors, if the worker's code tried to use the cleared field.  We can
fix that by creating a separate bool field to record whether the entry
needs to be revalidated.  (In the back branches, cram the bool into
what had been padding space, to avoid an ABI break in the somewhat
unlikely event that any extension is looking at this struct.)

Also, rearrange the logic in logicalrep_rel_open so that it
does the right thing in cases where table_open would fail.
We should retry the lookup by name in that case, but we didn't.

The real-world impact of this is probably small.  In the first place,
the error conditions are very low probability, and in the second place,
the worker would just exit and get restarted.  We only noticed because
in a CLOBBER_CACHE_ALWAYS build, the failure can occur repeatedly,
preventing the worker from making progress.  Nonetheless, it's clearly
a bug, and it impedes a useful type of testing; so back-patch to v10
where this code was introduced.

Discussion: https://postgr.es/m/1032727.1600096803@sss.pgh.pa.us

Commit b8fdee7d added leader_pid field into csvlog,
but forgot to update the example of file_fdw for csvlog.

Author: Yuta Katsuragi

Those extra queries are not necessary when doing a data-only dump.  With
this change, this means that the dependencies between CHECK/DEFAULT and
the parent table are not tracked anymore for a data-only dump.  However,
these dependencies are only used for the schema generation and we have
never guaranteed that a dump can be reloaded if a CHECK constraint uses
a custom function whose behavior changes when loading the data, like
when using cross-table references in the CHECK function.

Author: Julien Rouhaud
Reviewed-by: Daniel Gustafsson, Michael Paquier
Discussion: https://postgr.es/m/20200712054850.GA92357@nol

Previously, it was based on nBlocksAllocated to account for tapes with
open write buffers that may not have made it to the BufFile yet.

That was unnecessary, because callers do not need to get the number of
blocks while a tape has an open write buffer; and it also conflicted
with the preallocation logic added for HashAgg.

Reviewed-by: Peter Geoghegan
Discussion: https://postgr.es/m/ce5af05900fdbd0e9185747825a7423c48501964.camel@j-davis.com
Backpatch-through: 13

This was an oversight. The purpose of 7fdd919a was to avoid keeping
tape buffers around unnecessisarily, but HashAgg didn't rewind early
enough.

Reviewed-by: Peter Geoghegan
Discussion: https://postgr.es/m/1fb1151c2cddf8747d14e0532da283c3f97e2685.camel@j-davis.com
Backpatch-through: 13

In commit 46482432, for each RelationSyncEntry we maintained the list
of xids (streamed_txns) for which we have already sent the schema. This
helps us to track when to send the schema to the downstream node for
replication of streaming transactions. Before this list got initialized,
we were processing invalidation messages which access this list and led
to an assertion failure.

In passing, clean up the nearby code:

* Initialize the list of xids with NIL instead of NULL which is our usual
coding practice.
* Remove the MemoryContext switch for creating a RelationSyncEntry in dynahash.

Diagnosed-by: Amit Kapila and Tom Lane
Author: Amit Kapila
Reviewed-by: Tom Lane and Dilip Kumar
Discussion: https://postgr.es/m/904373.1600033123@sss.pgh.pa.us

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