This commit introduces new foreign data wrapper API for TRUNCATE.
It extends TRUNCATE command so that it accepts foreign tables as
the targets to truncate and invokes that API. Also it extends postgres_fdw
so that it can issue TRUNCATE command to foreign servers, by adding
new routine for that TRUNCATE API.

The information about options specified in TRUNCATE command, e.g.,
ONLY, CACADE, etc is passed to FDW via API. The list of foreign tables to
truncate is also passed to FDW. FDW truncates the foreign data sources
that the passed foreign tables specify, based on those information.
For example, postgres_fdw constructs TRUNCATE command using them
and issues it to the foreign server.

For performance, TRUNCATE command invokes the FDW routine for
TRUNCATE once per foreign server that foreign tables to truncate belong to.

Author: Kazutaka Onishi, Kohei KaiGai, slightly modified by Fujii Masao
Reviewed-by: Bharath Rupireddy, Michael Paquier, Zhihong Yu, Alvaro Herrera, Stephen Frost, Ashutosh Bapat, Amit Langote, Daniel Gustafsson, Ibrar Ahmed, Fujii Masao
Discussion: https://postgr.es/m/CAOP8fzb_gkReLput7OvOK+8NHgw-RKqNv59vem7=524krQTcWA@mail.gmail.com
Discussion: https://postgr.es/m/CAJuF6cMWDDqU-vn_knZgma+2GMaout68YUgn1uyDnexRhqqM5Q@mail.gmail.com

ScalarArrayOpExprs with "useOr=true" and a set of Consts on the righthand
side have traditionally been evaluated by using a linear search over the
array.  When these arrays contain large numbers of elements then this
linear search could become a significant part of execution time.

Here we add a new method of evaluating ScalarArrayOpExpr expressions to
allow them to be evaluated by first building a hash table containing each
element, then on subsequent evaluations, we just probe that hash table to
determine if there is a match.

The planner is in charge of determining when this optimization is possible
and it enables it by setting hashfuncid in the ScalarArrayOpExpr.  The
executor will only perform the hash table evaluation when the hashfuncid
is set.

This means that not all cases are optimized. For example CHECK constraints
containing an IN clause won't go through the planner, so won't get the
hashfuncid set.  We could maybe do something about that at some later
date.  The reason we're not doing it now is from fear that we may slow
down cases where the expression is evaluated only once.  Those cases can
be common, for example, a single row INSERT to a table with a CHECK
constraint containing an IN clause.

In the planner, we enable this when there are suitable hash functions for
the ScalarArrayOpExpr's operator and only when there is at least
MIN_ARRAY_SIZE_FOR_HASHED_SAOP elements in the array.  The threshold is
currently set to 9.

Author: James Coleman, David Rowley
Reviewed-by: David Rowley, Tomas Vondra, Heikki Linnakangas
Discussion: https://postgr.es/m/CAAaqYe8x62+=wn0zvNKCj55tPpg-JBHzhZFFc6ANovdqFw7-dA@mail.gmail.com

Introduce a new GUC recovery_prefetch, disabled by default.  When
enabled, look ahead in the WAL and try to initiate asynchronous reading
of referenced data blocks that are not yet cached in our buffer pool.
For now, this is done with posix_fadvise(), which has several caveats.
Better mechanisms will follow in later work on the I/O subsystem.

The GUC maintenance_io_concurrency is used to limit the number of
concurrent I/Os we allow ourselves to initiate, based on pessimistic
heuristics used to infer that I/Os have begun and completed.

The GUC wal_decode_buffer_size is used to limit the maximum distance we
are prepared to read ahead in the WAL to find uncached blocks.

Reviewed-by: Alvaro Herrera <alvherre@2ndquadrant.com> (parts)
Reviewed-by: Andres Freund <andres@anarazel.de> (parts)
Reviewed-by: Tomas Vondra <tomas.vondra@2ndquadrant.com> (parts)
Tested-by: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Tested-by: Jakub Wartak <Jakub.Wartak@tomtom.com>
Tested-by: Dmitry Dolgov <9erthalion6@gmail.com>
Tested-by: Sait Talha Nisanci <Sait.Nisanci@microsoft.com>
Discussion: https://postgr.es/m/CA%2BhUKGJ4VJN8ttxScUFM8dOKX0BrBiboo5uz1cq%3DAovOddfHpA%40mail.gmail.com

Teach xlogreader.c to decode its output into a circular buffer, to
support optimizations based on looking ahead.

 * XLogReadRecord() works as before, consuming records one by one, and
   allowing them to be examined via the traditional XLogRecGetXXX()
   macros.

 * An alternative new interface XLogNextRecord() is added that returns
   pointers to DecodedXLogRecord structs that can be examined directly.

 * XLogReadAhead() provides a second cursor that lets you see
   further ahead, as long as data is available and there is enough space
   in the decoding buffer.  This returns DecodedXLogRecord pointers to the
   caller, but also adds them to a queue of records that will later be
   consumed by XLogNextRecord()/XLogReadRecord().

The buffer's size is controlled with wal_decode_buffer_size.  The buffer
could potentially be placed into shared memory, for future projects.
Large records that don't fit in the circular buffer are called
"oversized" and allocated separately with palloc().

Discussion: https://postgr.es/m/CA+hUKGJ4VJN8ttxScUFM8dOKX0BrBiboo5uz1cq=AovOddfHpA@mail.gmail.com

Previously, the XLogReader module would fetch new input data using a
callback function.  Redesign the interface so that it tells the caller
to insert more data with a special return value instead.  This API suits
later patches for prefetching, encryption and maybe other future
projects that would otherwise require continually extending the callback
interface.

As incidental cleanup work, move global variables readOff, readLen and
readSegNo inside XlogReaderState.

Author: Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>
Author: Heikki Linnakangas <hlinnaka@iki.fi> (parts of earlier version)
Reviewed-by: Antonin Houska <ah@cybertec.at>
Reviewed-by: Alvaro Herrera <alvherre@2ndquadrant.com>
Reviewed-by: Takashi Menjo <takashi.menjo@gmail.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Thomas Munro <thomas.munro@gmail.com>
Discussion: https://postgr.es/m/20190418.210257.43726183.horiguchi.kyotaro%40lab.ntt.co.jp

There was some code in gen_prune_steps_from_opexps that needlessly
checked a list was not empty when it clearly had to contain at least one
item. This prompted a further cleanup operation in partprune.c.

Additionally, the previous code could end up adding additional needless
INTERSECT steps. However, those do not appear to be able to cause any
misbehavior.

gen_prune_steps_from_opexps is now no longer in charge of generating
combine pruning steps. Instead, gen_partprune_steps_internal, which
already does some combine step creation has been given the sole
responsibility of generating all combine steps. This means that when
we recursively call gen_partprune_steps_internal, since it always now adds
a combine step when it produces multiple steps, we can just pay attention
to the final step returned.

In passing, do quite a bit of work on the comments to try to more clearly
explain the role of both gen_partprune_steps_internal and
gen_prune_steps_from_opexps. This is fairly complex code so some extra
effort to give any new readers an overview of how things work seems like
a good idea.

Author: Amit Langote
Reported-by: Andy Fan
Reviewed-by: Kyotaro Horiguchi, Andy Fan, Ryan Lambert, David Rowley
Discussion: https://postgr.es/m/CAKU4AWqWoVii+bRTeBQmeVW+PznkdO8DfbwqNsu9Gj4ubt9A6w@mail.gmail.com

Apparently, an unrelated patch introduced some variation on the build
farm.
Reported-by: Magnus Hagander <magnus@hagander.net>

This adds a function, pg_wait_for_backend_termination(), and a new
timeout argument to pg_terminate_backend(), which will wait for the
backend to actually terminate (with or without signaling it to do so
depending on which function is called). The default behaviour of
pg_terminate_backend() remains being timeout=0 which does not waiting.
For pg_wait_for_backend_termination() the default wait is 5 seconds.

Author: Bharath Rupireddy
Reviewed-By: Fujii Masao, David Johnston, Muhammad Usama,
             Hou Zhijie, Magnus Hagander
Discussion: https://postgr.es/m/CALj2ACUBpunmyhYZw-kXCYs5NM+h6oG_7Df_Tn4mLmmUQifkqA@mail.gmail.com

Update src/tutorial/basics.source to match.

Author: Jürgen Purtz <juergen@purtz.de>
Reviewed-by: Thomas Munro <thomas.munro@gmail.com>
Reviewed-by: "David G. Johnston" <david.g.johnston@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/158996922318.7035.10603922579567326239@wrigleys.postgresql.org

Changing pg_stat_statements.track between 'all' and 'top' would control
if pg_stat_statements tracked just top level statements or also
statements inside functions, but when tracking all it would not
differentiate between the two. Being table to differentiate this is
useful both to track where the actual query is coming from, and to see
if there are differences in executions between the two.

To do this, add a boolean to the hash key indicating if the statement
was top level or not.

Experience from the pg_stat_kcache module shows that in at least some
"reasonable worloads" only <5% of the queries show up both top level and
nested. Based on this, admittedly small, dataset, this patch does not
try to de-duplicate those query *texts*, and will just store one copy
for the top level and one for the nested.

Author: Julien Rohaud
Reviewed-By: Magnus Hagander, Masahiro Ikeda
Discussion: https://postgr.es/m/20201202040516.GA43757@nol

If you know the ID of a buffer that recently held a block that you would
like to pin, this function can be used check if it's still there.  It
can be used to avoid a second lookup in the buffer mapping table after
PrefetchBuffer() reports a cache hit.
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/CA+hUKGJ4VJN8ttxScUFM8dOKX0BrBiboo5uz1cq=AovOddfHpA@mail.gmail.com

Previously, autovacuum would completely ignore partitioned tables, which
is not good regarding analyze -- failing to analyze those tables means
poor plans may be chosen.  Make autovacuum aware of those tables by
propagating "changes since analyze" counts from the leaf partitions up
the partitioning hierarchy.

This also introduces necessary reloptions support for partitioned tables
(autovacuum_enabled, autovacuum_analyze_scale_factor,
autovacuum_analyze_threshold).  It's unclear how best to document this
aspect.

Author: Yuzuko Hosoya <yuzukohosoya@gmail.com>
Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Reviewed-by: Tomas Vondra <tomas.vondra@enterprisedb.com>
Reviewed-by: Álvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://postgr.es/m/CAKkQ508_PwVgwJyBY=0Lmkz90j8CmWNPUxgHvCUwGhMrouz6UA@mail.gmail.com

It's far from clear that this is the right approach - but a good
portion of the buildfarm has been red for a few hours, on the last day
of the CF. And this fixes at least the obvious crash. So let's go with
that for now.

Discussion: https://postgr.es/m/20210407225806.majgznh4lk34hjvu%40alap3.anarazel.de

Author: Tatsuro Yamada
Discussion: https://postgr.es/m/7c166a60-2808-6b89-9524-feefc6233748@nttcom.co.jp_1

When working on a scan with only a catalog snapshot, we may not have an
ActiveSnapshot set.  If we were to come across a detached partition,
that would cause a crash.  Fix by only ignoring detached partitions when
there's an active snapshot.

When dealing with overloaded function or operator names, having
to look through a long list of matches is tedious.  Let's extend
these commands to allow specification of (input) argument types
to let such results be trimmed down.  Each additional argument
is treated the same as the pattern argument of \dT and matched
against the appropriate argument's type name.

While at it, fix \dT (and these new options) to recognize the
usual notation of "foo[]" for "the array type over foo", and
to handle the special abbreviations allowed by the backend
grammar, such as "int" for "integer".

Greg Sabino Mullane, revised rather significantly by me

Discussion: https://postgr.es/m/CAKAnmmLF9Hhu02N+s7uAyLc5J1xZReg72HQUoiKhNiJV3_jACQ@mail.gmail.com

This also adjusts the printf format for query id used by log_line_prefix
(%Q).

Reported-by: Justin Pryzby

Discussion: https://postgr.es/m/20210408005402.GG24239@momjian.us

Author: Julien Rouhaud, Bruce Momjian

VACUUM has never needed to call ambulkdelete() for each index in cases
where there are precisely zero TIDs in its dead_tuples array by the end
of its first pass over the heap (also its only pass over the heap in
this scenario).  Index vacuuming is simply not required when this
happens.  Index cleanup will still go ahead, but in practice most calls
to amvacuumcleanup() are usually no-ops when there were zero preceding
ambulkdelete() calls.  In short, VACUUM has generally managed to avoid
index scans when there were clearly no index tuples to delete from
indexes.  But cases with _close to_ no index tuples to delete were
another matter -- a round of ambulkdelete() calls took place (one per
index), each of which performed a full index scan.

VACUUM now behaves just as if there were zero index tuples to delete in
cases where there are in fact "virtually zero" such tuples.  That is, it
can now bypass index vacuuming and heap vacuuming as an optimization
(though not index cleanup).  Whether or not VACUUM bypasses indexes is
determined dynamically, based on the just-observed number of heap pages
in the table that have one or more LP_DEAD items (LP_DEAD items in heap
pages have a 1:1 correspondence with index tuples that still need to be
deleted from each index in the worst case).

We only skip index vacuuming when 2% or less of the table's pages have
one or more LP_DEAD items -- bypassing index vacuuming as an
optimization must not noticeably impede setting bits in the visibility
map.  As a further condition, the dead_tuples array (i.e. VACUUM's array
of LP_DEAD item TIDs) must not exceed 32MB at the point that the first
pass over the heap finishes, which is also when the decision to bypass
is made.  (The VACUUM must also have been able to fit all TIDs in its
maintenance_work_mem-bound dead_tuples space, though with a default
maintenance_work_mem setting it can't matter.)

This avoids surprising jumps in the duration and overhead of routine
vacuuming with workloads where successive VACUUM operations consistently
have almost zero dead index tuples.  The number of LP_DEAD items may
well accumulate over multiple VACUUM operations, before finally the
threshold is crossed and VACUUM performs conventional index vacuuming.
Even then, the optimization will have avoided a great deal of largely
unnecessary index vacuuming.

In the future we may teach VACUUM to skip index vacuuming on a per-index
basis, using a much more sophisticated approach.  For now we only
consider the extreme cases, where we can be quite confident that index
vacuuming just isn't worth it using simple heuristics.

Also log information about how many heap pages have one or more LP_DEAD
items when autovacuum logging is enabled.

Author: Masahiko Sawada <sawada.mshk@gmail.com>
Author: Peter Geoghegan <pg@bowt.ie>
Discussion: https://postgr.es/m/CAD21AoD0SkE11fMw4jD4RENAwBMcw1wasVnwpJVw3tVqPOQgAw@mail.gmail.com
Discussion: https://postgr.es/m/CAH2-WzmkebqPd4MVGuPTOS9bMFvp9MDs5cRTCOsv1rQJ3jCbXw@mail.gmail.com

The query originally used was too simple, cause explain_filter() to be
unable to remove JIT output text.

Reported-by: Tom Lane

Author: Julien Rouhaud

The truncation of the log file, that this set of tests relies on to make
sure that a connection attempt matches with its expected backend log
pattern, fails, as reported by buildfarm member fairywren.  Instead of a
truncation, do a rotation of the log file and restart the node.  This
will ensure that the connection attempt data is unique for each test.

Discussion: https://postgr.es/m/YG05nCI8x8B+Ad3G@paquier.xyz

This adds support for writing CREATE FUNCTION and CREATE PROCEDURE
statements for language SQL with a function body that conforms to the
SQL standard and is portable to other implementations.

Instead of the PostgreSQL-specific AS $$ string literal $$ syntax,
this allows writing out the SQL statements making up the body
unquoted, either as a single statement:

    CREATE FUNCTION add(a integer, b integer) RETURNS integer
        LANGUAGE SQL
        RETURN a + b;

or as a block

    CREATE PROCEDURE insert_data(a integer, b integer)
    LANGUAGE SQL
    BEGIN ATOMIC
      INSERT INTO tbl VALUES (a);
      INSERT INTO tbl VALUES (b);
    END;

The function body is parsed at function definition time and stored as
expression nodes in a new pg_proc column prosqlbody.  So at run time,
no further parsing is required.

However, this form does not support polymorphic arguments, because
there is no more parse analysis done at call time.

Dependencies between the function and the objects it uses are fully
tracked.

A new RETURN statement is introduced.  This can only be used inside
function bodies.  Internally, it is treated much like a SELECT
statement.

psql needs some new intelligence to keep track of function body
boundaries so that it doesn't send off statements when it sees
semicolons that are inside a function body.
Tested-by: Jaime Casanova <jcasanov@systemguards.com.ec>
Reviewed-by: Julien Rouhaud <rjuju123@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/1c11f1eb-f00c-43b7-799d-2d44132c02d7@2ndquadrant.com

Add a failsafe mechanism that is triggered by VACUUM when it notices
that the table's relfrozenxid and/or relminmxid are dangerously far in
the past.  VACUUM checks the age of the table dynamically, at regular
intervals.

When the failsafe triggers, VACUUM takes extraordinary measures to
finish as quickly as possible so that relfrozenxid and/or relminmxid can
be advanced.  VACUUM will stop applying any cost-based delay that may be
in effect.  VACUUM will also bypass any further index vacuuming and heap
vacuuming -- it only completes whatever remaining pruning and freezing
is required.  Bypassing index/heap vacuuming is enabled by commit
8523492d, which made it possible to dynamically trigger the mechanism
already used within VACUUM when it is run with INDEX_CLEANUP off.

It is expected that the failsafe will almost always trigger within an
autovacuum to prevent wraparound, long after the autovacuum began.
However, the failsafe mechanism can trigger in any VACUUM operation.
Even in a non-aggressive VACUUM, where we're likely to not advance
relfrozenxid, it still seems like a good idea to finish off remaining
pruning and freezing.   An aggressive/anti-wraparound VACUUM will be
launched immediately afterwards.  Note that the anti-wraparound VACUUM
that follows will itself trigger the failsafe, usually before it even
begins its first (and only) pass over the heap.

The failsafe is controlled by two new GUCs: vacuum_failsafe_age, and
vacuum_multixact_failsafe_age.  There are no equivalent reloptions,
since that isn't expected to be useful.  The GUCs have rather high
defaults (both default to 1.6 billion), and are expected to generally
only be used to make the failsafe trigger sooner/more frequently.

Author: Masahiko Sawada <sawada.mshk@gmail.com>
Author: Peter Geoghegan <pg@bowt.ie>
Discussion: https://postgr.es/m/CAD21AoD0SkE11fMw4jD4RENAwBMcw1wasVnwpJVw3tVqPOQgAw@mail.gmail.com
Discussion: https://postgr.es/m/CAH2-WzmgH3ySGYeC-m-eOBsa2=sDwa292-CFghV4rESYo39FsQ@mail.gmail.com

Use the in-core query id computation for pg_stat_activity,
log_line_prefix, and EXPLAIN VERBOSE.

Similar to other fields in pg_stat_activity, only the queryid from the
top level statements are exposed, and if the backends status isn't
active then the queryid from the last executed statements is displayed.

Add a %Q placeholder to include the queryid in log_line_prefix, which
will also only expose top level statements.

For EXPLAIN VERBOSE, if a query identifier has been computed, either by
enabling compute_query_id or using a third-party module, display it.

Bump catalog version.

Discussion: https://postgr.es/m/20210407125726.tkvjdbw76hxnpwfi@nol

Author: Julien Rouhaud

Reviewed-by: Alvaro Herrera, Nitin Jadhav, Zhihong Yu

First, don't perform database access while holding a buffer lock.
When checking a heap, we can validate that TOAST pointers are sane by
performing a scan on the TOAST index and looking up the chunks that
correspond to each value ID that appears in a TOAST poiner in the main
table. But, to do that while holding a buffer lock at least risks
causing other backends to wait uninterruptibly, and probably can cause
undetected and uninterruptible deadlocks.  So, instead, make a list of
checks to perform while holding the lock, and then perform the checks
after releasing it.

Second, adjust things so that we don't try to follow TOAST pointers
for tuples that are already eligible to be pruned. The TOAST tuples
become eligible for pruning at the same time that the main tuple does,
so trying to check them may lead to spurious reports of corruption,
as observed in the buildfarm. The necessary infrastructure to decide
whether or not the tuple being checked is prunable was added by
commit 3b6c1259, but it wasn't
actually used for its intended purpose prior to this patch.

Mark Dilger, adjusted by me to avoid a memory leak.

Discussion: http://postgr.es/m/AC5479E4-6321-473D-AC92-5EC36299FBC2@enterprisedb.com

Add compute_query_id GUC to control whether a query identifier should be
computed by the core (off by default).  It's thefore now possible to
disable core queryid computation and use pg_stat_statements with a
different algorithm to compute the query identifier by using a
third-party module.

To ensure that a single source of query identifier can be used and is
well defined, modules that calculate a query identifier should throw an
error if compute_query_id specified to compute a query id and if a query
idenfitier was already calculated.

Discussion: https://postgr.es/m/20210407125726.tkvjdbw76hxnpwfi@nol

Author: Julien Rouhaud

Reviewed-by: Alvaro Herrera, Nitin Jadhav, Zhihong Yu

This fails on older OpenSSL versions that lack channel binding
support.  Since that feature is not essential to this test case,
just remove it, instead of complicating matters.  Per buildfarm.

Jacob Champion

Discussion: https://postgr.es/m/fa8dbbb58c20b1d1adf0082769f80d5466eaf485.camel@vmware.com

Amit Langote

Discussion: https://postgr.es/m/CA+HiwqEcawatEaUh1uTbZMEZTJeLzbroRTz9_X9Z5CFjTWJkhw@mail.gmail.com

Commit 3b6c1259 resulted in the same
xmin and xmax bounds checking being performed in both check_tuple()
and check_tuple_visibility(). Remove the duplication.

While at it, adjust some code comments that were overlooked in that
commit.

Mark Dilger

Discussion: http://postgr.es/m/AC5479E4-6321-473D-AC92-5EC36299FBC2@enterprisedb.com

Teach VACUUM to truncate the line pointer array of each heap page when a
contiguous group of LP_UNUSED line pointers appear at the end of the
array -- these unused and unreferenced items are excluded.  This process
occurs during VACUUM's second pass over the heap, right after LP_DEAD
line pointers on the page (those encountered/pruned during the first
pass) are marked LP_UNUSED.

Truncation avoids line pointer bloat with certain workloads,
particularly those involving continual range DELETEs and bulk INSERTs
against the same table.

Also harden heapam code to check for an out-of-range page offset number
in places where we weren't already doing so.

Author: Matthias van de Meent <boekewurm+postgres@gmail.com>
Author: Peter Geoghegan <pg@bowt.ie>
Reviewed-By: Masahiko Sawada <sawada.mshk@gmail.com>
Reviewed-By: Peter Geoghegan <pg@bowt.ie>
Discussion: https://postgr.es/m/CAEze2WjgaQc55Y5f5CQd3L=eS5CZcff2Obxp=O6pto8-f0hC4w@mail.gmail.com
Discussion: https://postgr.es/m/CAH2-Wzn6a64PJM1Ggzm=uvx2otsopJMhFQj_g1rAj4GWr3ZSzw@mail.gmail.com

Formerly we were pretty lax about what a custom GUC's name could
be; so long as it had at least one dot in it, we'd take it.
However, corner cases such as dashes or equal signs in the name
would cause various bits of functionality to misbehave.  Rather
than trying to make the world perfectly safe for that, let's
just require that custom names look like "identifier.identifier",
where "identifier" means something that scan.l would accept
without double quotes.

Along the way, this patch refactors things slightly in guc.c
so that find_option() is responsible for reporting GUC-not-found
cases, allowing removal of duplicative code from its callers.

Per report from Hubert Depesz Lubaczewski.  No back-patch,
since the consequences of the problem don't seem to warrant
changing behavior in stable branches.

Discussion: https://postgr.es/m/951335.1612910077@sss.pgh.pa.us

The code in bringetbitmap() simply added the whole matching page range
to the TID bitmap, as determined by pages_per_range, even if some of the
pages were beyond the end of the heap. The query then might fail with
an error like this:

  ERROR:  could not open file "base/20176/20228.2" (target block
          262144): previous segment is only 131021 blocks

In this case, the relation has 262093 pages (131072 and 131021 pages),
but we're trying to acess block 262144, i.e. first block of the 3rd
segment. At that point _mdfd_getseg() notices the preceding segment is
incomplete, and fails.

Hitting this in practice is rather unlikely, because:

* Most indexes use power-of-two ranges, so segments and page ranges
  align perfectly (segment end is also a page range end).

* The table size has to be just right, with the last segment being
  almost full - less than one page range from full segment, so that the
  last page range actually crosses the segment boundary.

* Prefetch has to be enabled. The regular page access checks that
  pages are not beyond heap end, but prefetch does not. On older
  releases (before 12) the execution stops after hitting the first
  non-existent page, so the prefetch distance has to be sufficient
  to reach the first page in the next segment to trigger the issue.
  Since 12 it's enough to just have prefetch enabled, the prefetch
  distance does not matter.

Fixed by not adding non-existent pages to the TID bitmap. Backpatch
all the way back to 9.6 (BRIN indexes were introduced in 9.5, but that
release is EOL).

Backpatch-through: 9.6

By default, have libpq set the TLS extension "Server Name Indication" (SNI).

This allows an SNI-aware SSL proxy to route connections.  (This
requires a proxy that is aware of the PostgreSQL protocol, not just
any SSL proxy.)

In the future, this could also allow the server to use different SSL
certificates for different host specifications.  (That would require
new server functionality.  This would be the client-side functionality
for that.)

Since SNI makes the host name appear in cleartext in the network
traffic, this might be undesirable in some cases.  Therefore, also add
a libpq connection option "sslsni" to turn it off.

Discussion: https://www.postgresql.org/message-id/flat/7289d5eb-62a5-a732-c3b9-438cee2cb709%40enterprisedb.com

The previous implementation (from 9afffcb8) had an unnecessary check
on the boundaries of the enum which trigtered compile warnings. To clean
it up, move the pre-existing static assert to a central location and
call that.

Reported-By: Erik Rijkers
Reviewed-By: Michael Paquier
Discussion: https://postgr.es/m/1056399262.13159.1617793249020@webmailclassic.xs4all.nl

Discussion: https://www.postgresql.org/message-id/flat/161626776179.652.11944895442156126506%40wrigleys.postgresql.org

This reverts commit 9f984ba6.

It was making the buildfarm unhappy, apparently setting client_min_messages
in a regression test produces different output if log_statement='all'.
Another issue is that I now suspect the bit sortsupport function was in
fact not correct to call byteacmp(). Revert to investigate both of those
issues.

Commit 16fa9b2b introduced a faster way to build GiST indexes, by
sorting all the data. This commit adds the sortsupport functions needed
to make use of that feature for btree_gist.

Author: Andrey Borodin
Discussion: https://www.postgresql.org/message-id/2F3F7265-0D22-44DB-AD71-8554C743D943@yandex-team.ru

Documentation and comments in code and tests have been using the terms
sensitive/insensitive cursor incorrectly relative to the SQL standard.
(Cursor sensitivity is only relevant for changes made in the same
transaction as the cursor, not for concurrent changes in other
sessions.)  Moreover, some of the behavior of PostgreSQL is incorrect
according to the SQL standard, confusing the issue further.  (WHERE
CURRENT OF changes are not visible in insensitive cursors, but they
should be.)

This change corrects the terminology and removes the claim that
sensitive cursors are supported.  It also adds a test case that checks
the insensitive behavior in a "correct" way, using a change command
not using WHERE CURRENT OF.  Finally, it adds the ASENSITIVE cursor
option to select the default asensitive behavior, per SQL standard.

There are no changes to cursor behavior in this patch.

Discussion: https://www.postgresql.org/message-id/flat/96ee8b30-9889-9e1b-b053-90e10c050e85%40enterprisedb.com

The previous wording contained a superfluous comma.  Adjust phrasing
for grammatical correctness and clarity.

Bloom, GIN, GiST and SP-GiST rely on PageInit() to initialize the
contents of a page, and this routine fills entirely a page with zeros
for a size of BLCKSZ, including the special space.  Those index AMs have
been using an extra memset() call to fill with zeros the special page
space, or even the whole page, which is not necessary as PageInit()
already does this work, so let's remove them.  GiST was not doing this
extra call, but has commented out a system call that did so since
62369911.

While on it, remove one MAXALIGN() for SP-GiST as PageInit() takes care
of that.  This makes the whole page initialization logic more consistent
across all index AMs.

Author: Bharath Rupireddy
Reviewed-by: Vignesh C, Mahendra Singh Thalor
Discussion: https://postgr.es/m/CALj2ACViOo2qyaPT7krWm4LRyRTw9kOXt+g6PfNmYuGA=YHj9A@mail.gmail.com