This is cleanup for commit 27e1f145:

* ExecAppendAsyncEventWait(), which was modified a bit further by commit
  a8af856d, duplicated the same nevents calculation.  Simplify the code
  a little bit to avoid the duplication.  Update comments there.
* Add an assertion to ExecAppendAsyncRequest().
* Update a comment about merging the async_capable options from input
  relations in merge_fdw_options(), per complaint from Kyotaro Horiguchi.
* Add a comment for fetch_more_data_begin().

Author: Etsuro Fujita
Discussion: https://postgr.es/m/CAPmGK1637W30Wx3MnrReewhafn6F_0J76mrJGoFXFnpPq4QfvA%40mail.gmail.com

Adopt a more consistent policy about what slot-type-specific
getsysattr functions should do when system attributes are not
available.  To wit, they should all throw the same user-oriented
error, rather than variously crashing or emitting developer-oriented
messages.

This closes a identifiable problem in commits a71cfc56b and
3fb93103a (in v13 and v12), so back-patch into those branches,
along with a test case to try to ensure we don't break it again.
It is not known that any of the former crash cases are reachable
in HEAD, but this seems like a good safety improvement in any case.

Discussion: https://postgr.es/m/141051591267657@mail.yandex.ru

Have interested callers of find_inheritance_children set the
detached_exist value to false prior to calling it, so that that routine
only has to set it true in the rare cases where it is necessary.  Don't
touch it otherwise.

Per buildfarm member thorntail (which reported a UBSan failure here).

This was discussed in commit 9081bddb.

Reported-by: Peter Eisentraut

Discussion: https://postgr.es/m/flat/87o8pco34z.fsf@wibble.ilmari.org

per gripe from Alvaro Herrera.

During queries coming from ri_triggers.c, we need to omit partitions
that are marked pending detach -- otherwise, the RI query is tricked
into allowing a row into the referencing table whose corresponding row
is in the detached partition.  Which is bogus: once the detach operation
completes, the row becomes an orphan.

However, the code was not doing that in repeatable-read transactions,
because relcache kept a copy of the partition descriptor that included
the partition, and used it in the RI query.  This commit changes the
partdesc cache code to only keep descriptors that aren't dependent on
a snapshot (namely: those where no detached partition exist, and those
where detached partitions are included).  When a partdesc-without-
detached-partitions is requested, we create one afresh each time; also,
those partdescs are stored in PortalContext instead of
CacheMemoryContext.

find_inheritance_children gets a new output *detached_exist boolean,
which indicates whether any partition marked pending-detach is found.
Its "include_detached" input flag is changed to "omit_detached", because
that name captures desired the semantics more naturally.
CreatePartitionDirectory() and RelationGetPartitionDesc() arguments are
identically renamed.

This was noticed because a buildfarm member that runs with relcache
clobbering, which would not keep the improperly cached partdesc, broke
one test, which led us to realize that the expected output of that test
was bogus.  This commit also corrects that expected output.

Author: Amit Langote <amitlangote09@gmail.com>
Author: Álvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://postgr.es/m/3269784.1617215412@sss.pgh.pa.us

Back-patch to v13; the table layout in older branches is unfriendly
to adding such details.

Laurenz Albe

Discussion: https://postgr.es/m/161881920775.685.12293798764864559341@wrigleys.postgresql.org

A new PostgresVersion object type is created and this is used in
PostgresNode using the output of `pg_config --version` and the result
stored in the PostgresNode object.  This object can be compared to other
PostgresVersion objects, or to a number or string.

PostgresNode is currently believed to be compatible with versions down
to release 12, so PostgresNode will issue a warning if used with a
version prior to that.

No attempt has been made to deal with incompatibilities in older
versions - that remains work to be undertaken in a subsequent
development cycle.

Based on code from Mark Dilger and Jehan-Guillaume de Rorthais.

Discussion: https://postgr.es/m/a80421c0-3d7e-def1-bcfe-24777f15e344@dunslane.net

Creating a trigger on a relation to which an apply operation is
triggered would cause a relation leak once the change gets committed,
as the executor would miss that the relation needs to be closed
beforehand.  This issue got introduced with the refactoring done in
1375422c, where it becomes necessary to track relations within
es_opened_result_relations to make sure that they are closed.

We have discussed using ExecInitResultRelation() coupled with
ExecCloseResultRelations() for the relations in need of tracking by the
apply operations in the subscribers, which would simplify greatly the
opening and closing of indexes, but this requires a larger rework and
reorganization of the worker code, particularly for the tuple routing
part.  And that's not really welcome post feature freeze.  So, for now,
settle down to the same solution as TRUNCATE which is to fill in
es_opened_result_relations with the relation opened, to make sure that
ExecGetTriggerResultRel() finds them and that they get closed.

The code is lightly refactored so as a relation is not registered three
times for each DML code path, making the whole a bit easier to follow.

Reported-by: Tang Haiying, Shi Yu, Hou Zhijie
Author: Amit Langote, Masahiko Sawada, Hou Zhijie
Reviewed-by: Amit Kapila, Michael Paquier
Discussion: https://postgr.es/m/OS0PR01MB611383FA0FE92EB9DE21946AFB769@OS0PR01MB6113.jpnprd01.prod.outlook.com

parallel_leader_participation got introduced in e5253fdc, where it was
listed under RESOURCES_ASYNCHRONOUS in guc.c, but the documentation
did not reflect that and listed it with the other planner-related
options.  This commit fixes this inconsistency as the parameter is
intended to be an asynchronous one.

While on it, reorganize a bit the section dedicated to asynchronous
parameters, backend_flush_after being moved first to do better in terms
of alphabetical order of the options listed.

Reported-by: Yanliang Lei
Author: Bharath Rupireddy
Discussion: https://postgr.es/m/16972-42d4b0c15aa1d5f5@postgresql.org

Per observation from Tom Lane.

Discussion: https://postgr.es/m/1901125.1617904665@sss.pgh.pa.us

On ALTER TABLE .. DETACH CONCURRENTLY, we add a new table constraint
that duplicates the partition constraint.  But if the partition already
has another constraint that implies that one, then that's unnecessary.
We were already avoiding the addition of a duplicate constraint if there
was an exact 'equal' match -- this just improves the quality of the check.

Author: Justin Pryzby <pryzby@telsasoft.com>
Reviewed-by: Álvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://postgr.es/m/20210410184226.GY6592@telsasoft.com

This has been found to cause hangs where tcp usage is forced.

Alexey Kodratov

Discussion: https://postgr.es/m/82e271a9a11928337fcb5b5e57b423c0@postgrespro.ru

Backpatch to all live branches

Since pg_depend can contain duplicate entries, we need to eliminate
those in information schema views that build on pg_depend, using
DISTINCT.  Some of the older views already did that correctly, but
some of the more recently added ones didn't.  (In some of these views,
it might not be possible to reproduce the issue because of how the
implementation happens to deduplicate dependencies while recording
them, but it seems better to keep this consistent in all cases.)

Should be %u rather than %d.

Use %lld and cast to long long int instead.

Not enabling compute_query_id would disable pg_stat_statements even if
the module is listed in shared_preload_libraries, so add it to the
minimum configuration set as listed in its documentation.

Author: Greg Nancarrow
Reviewed-by: Julien Rouhaud, Bharath Rupireddy
Discussion: https://postgr.es/m/CAJcOf-fXyb2QiDbwftD813UF70w-+BsK-03bFp1GrijXU9GQYQ@mail.gmail.com

This compatibility has been added in 45b98057, but psql forgot the call.

Author: Wei Wang
Reviewed-by: Aleksander Alekseev
Discussion: https://postgr.es/m/OS3PR01MB6275935F62E161BCD393D6559E489@OS3PR01MB6275.jpnprd01.prod.outlook.com

While tracking down the bug fixed in the preceding commit, I got quite
annoyed by the low quality of spg_desc's output.  Add missing fields,
try to make the formatting consistent.

Commit f003d9f8 left this macro with inadequate (or, one could say,
too much) parenthesization.  Which was catastrophic to the correctness
of calls such as "if (!XLogRecHasBlockRef(record, 1)) ...".  There
are only a few of those, which perhaps explains why we didn't notice
immediately (with our general weakness of WAL replay testing being
another factor).  I found it by debugging intermittent replay failures
like

2021-04-08 14:33:30.191 EDT [29463] PANIC:  failed to locate backup block with ID 1
2021-04-08 14:33:30.191 EDT [29463] CONTEXT:  WAL redo at 0/95D3438 for SPGist/ADD_NODE: off 1; blkref #0: rel 1663/16384/25998, blk 1

log_statement is issued before query_id can be computed, so properly
clear the value, and document the interaction.

Reported-by: Fujii Masao, Michael Paquier

Discussion: https://postgr.es/m/YHPkU8hFi4no4NSw@paquier.xyz

Author: Julien Rouhaud

Previously, it was pg_stat_activity.queryid to match the
pg_stat_statements queryid column.  This is an adjustment to patch
4f0b0966.  This also adjusts some of the internal function calls to
match.  Catversion bumped.

Reported-by: Álvaro Herrera, Julien Rouhaud

Discussion: https://postgr.es/m/20210408032704.GA7498@alvherre.pgsql

I didn't particularly like this function name, as it fails to
express what's going on.  Also, returning the sort expression
alone isn't too helpful --- typically, a caller would also
need some other fields of the EquivalenceMember.  But the
sole caller really only needs a bool result, so let's make
it "bool relation_can_be_sorted_early()".

Discussion: https://postgr.es/m/91f3ec99-85a4-fa55-ea74-33f85a5c651f@swarm64.com

An oversight introduced by the incremental-sort patches caused
"could not find pathkey item to sort" errors in some situations
where a sort key involves an aggregate or window function.

The basic problem here is that find_em_expr_usable_for_sorting_rel
isn't properly modeling what prepare_sort_from_pathkeys will do
later.  Rather than hoping we can keep those functions in sync,
let's refactor so that they actually share the code for
identifying a suitable sort expression.

With this refactoring, tlist.c's tlist_member_ignore_relabel
is unused.  I removed it in HEAD but left it in place in v13,
in case any extensions are using it.

Per report from Luc Vlaming.  Back-patch to v13 where the
problem arose.

James Coleman and Tom Lane

Discussion: https://postgr.es/m/91f3ec99-85a4-fa55-ea74-33f85a5c651f@swarm64.com

Commit b34ca595 provided for installation-aware instances of
PostgresNode. However, it turns out that IPC::Run works against this by
caching the path to a binary and not consulting the path again, even if
it has changed. We work around this by calling Postgres binaries with
the installed path rather than just a bare name to be looked up in the
environment path, if there is an installed path. For the common case
where there is no installed path we continue to use the bare command
name.

Diagnosis and solution from Mark Dilger

Discussion: https://postgr.es/m/E8F512F8-B4D6-4514-BA8D-2E671439DA92@enterprisedb.com

Author: Julien Rouhaud
Backpatch-through: 11
Discussion: https://postgr.es/m/20210420121659.odjueyd4rpilorn5@nol

Document VACUUM's soft assumption that any LP_DEAD items encountered
during pruning will become LP_UNUSED items before VACUUM finishes up.
This is integral to the accounting used by VACUUM to generate its final
report on the table to the stats collector.  It also affects how VACUUM
determines which heap pages are truncatable.  In both cases VACUUM is
concerned with the likely contents of the page in the near future, not
the current contents of the page.

This state of affairs created the false impression that VACUUM's dead
tuple accounting had significant difference with similar accounting used
during ANALYZE.  There were and are no substantive differences, at least
when the soft assumption completely works out.  This is far clearer now.

Also document cases where things don't quite work out for VACUUM's dead
tuple accounting.  It's possible that a significant number of LP_DEAD
items will be left behind by VACUUM, and won't be recorded as remaining
dead tuples in VACUUM's statistics collector report.  This behavior
dates back to commit a96c41fe, which taught VACUUM to run without index
and heap vacuuming at the user's request.  The failsafe mechanism added
to VACUUM more recently by commit 1e55e7d1 takes the same approach to
dead tuple accounting.
Reported-By: Masahiko Sawada <sawada.mshk@gmail.com>
Discussion: https://postgr.es/m/CAH2-Wz=Jmtu18PrsYq3EvvZJGOmZqSO2u3bvKpx9xJa5uhNp=Q@mail.gmail.com

Should be signed, not unsigned.

In the new test after resetting the stats, we were not waiting for the
stats message to be delivered. Also, we need to decode the results for
the new test, otherwise, it will show the old stats.

In passing,
a. Change docs added by commit f5fc2f5b as per suggestion by
Justin Pryzby.
b. Bump the PGSTAT_FILE_FORMAT_ID as commit f5fc2f5b changes the file
format of stats.

Reported-by: Tom Lane based on buildfarm reports
Author: Vignesh C, Justin Pryzby
Reviewed-by: Amit Kapila
Discussion: https://postgr.es/m/20210319185247.ldebgpdaxsowiflw@alap3.anarazel.de

Author: Justin Pryzby
Discussion: https://postgr.es/m/20210416070310.GG3315@telsasoft.com

A couple of tests have been using 0 as magic constant while SEEK_SET can
be used instead.  This makes the code easier to understand, and more
consistent with the changes done in 3c5b0685.

Per discussion with Andrew Dunstan.

Discussion: https://postgr.es/m/YHrc24AgJQ6tQ1q0@paquier.xyz

Add a few words of comment to explain why SIGURG doesn't follow the
dummy_handler pattern used for SIGUSR2, since that might otherwise
appear to be a bug.

Discussion: https://postgr.es/m/4006115.1618577212%40sss.pgh.pa.us

Should be %u rather than %d.