This reverts commit 096dd80f3ccc and its fixups beecbe8e5001, afdd9f7f0e00,
529da086ba, db93e739ac61.

Catversion is bumped.

Discussion: https://postgr.es/m/d46f9265-ff3c-6743-2278-6772598233c2%40pgmasters.net

This is equivalent to a revert of f193883 and fb32748, with the addition
that the declaration of the SQLValueFunction node needs to gain a couple
of node_attr for query jumbling.  The performance impact of removing the
function call inlining is proving to be too huge for some workloads
where these are used.  A worst-case test case of involving only simple
SELECT queries with a SQL keyword is proving to lead to a reduction of
10% in TPS via pgbench and prepared queries on a high-end machine.

None of the tests I ran back for this set of changes saw such a huge
gap, but Alexander Lakhin and Andres Freund have found that this can be
noticeable.  Keeping the older performance would mean to do more
inlining in the executor when using COERCE_SQL_SYNTAX for a function
expression, similarly to what SQLValueFunction does.  This requires more
redesign work and there is little time until 16beta1 is released, so for
now reverting the change is the best way forward, bringing back the
previous performance.

Bump catalog version.

Reported-by: Alexander Lakhin
Discussion: https://postgr.es/m/b32bed1b-0746-9b20-1472-4bdc9ca66d52@gmail.com

An update of the GUC stats_fetch_consistency in a transaction would be
able to trigger an assertion when doing cache->snapshot.  In this case,
when retrieving a pgstat entry after the switch, a new snapshot would be
rebuilt, confusing pgstat_build_snapshot() because a snapshot is already
cached with an unexpected mode ("cache").

In order to fix this problem, this commit adds a flag to force a
snapshot clear each time this GUC is changed.  Some tests are added to
check, while on it.

Some optimizations in avoiding the snapshot clear should be possible
depending on what is cached and the current GUC value, I guess, but this
solution is simple, and ensures that the state of the cache is updated
each time a new pgstat entry is fetched, hence being consistent with the
level wanted by the client that has set the GUC.

Note that cache->none and snapshot->none would not cause issues, as
fetching a pgstat entry would be retrieved from shared memory on the
second attempt, however a snapshot would still be cached.  Similarly,
none->snapshot and none->cache would build a new snapshot on the second
fetch attempt.  Finally, snapshot->cache would cache a new snapshot on
the second attempt.

Reported-by: Alexander Lakhin
Author: Kyotaro Horiguchi
Discussion: https://postgr.es/m/17804-2a118cd046f2d0e5@postgresql.org
backpatch-through: 15

Old versions of Solaris and illumos had buffer overrun bugs in their
strxfrm() implementations.  The bugs were fixed more than a decade ago
and the relevant releases are long out of vendor support.  It's time to
remove the defense added by commit be8b06c3.

Reviewed-by: Nathan Bossart <nathandbossart@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CA+hUKGJ-ZPJwKHVLbqye92-ZXeLoCHu5wJL6L6HhNP7FkJ=meA@mail.gmail.com

Author: Alexander Lakhin
Discussion: https://postgr.es/m/699beab4-a6ca-92c9-f152-f559caf6dc25@gmail.com

This fixes many spelling mistakes in comments, but a few references to
invalid parameter names, function names and option names too in comments
and also some in string constants

Also, fix an #undef that was undefining the incorrect definition

Author: Alexander Lakhin
Reviewed-by: Justin Pryzby
Discussion: https://postgr.es/m/d5f68d19-c0fc-91a9-118d-7c6a5a3f5fad@gmail.com

This reverts commit 3d03b24c3 (Revert Add support for Kerberos
credential delegation) which was committed on the grounds of concern
about portability, but on further review and discussion, it's clear that
we are better off explicitly requiring MIT Kerberos as that appears to
be the only GSSAPI library currently that's under proper maintenance
and ongoing development.  The API used for storing credentials was added
to MIT Kerberos over a decade ago while for the other libraries which
appear to be mainly based on Heimdal, which exists explicitly to be a
re-implementation of MIT Kerberos, the API never made it to a released
version (even though it was added to the Heimdal git repo over 5 years
ago..).

This post-feature-freeze change was approved by the RMT.

Discussion: https://postgr.es/m/ZDDO6jaESKaBgej0%40tamriel.snowman.net

This reverts commit 3d4fa227bce4294ce1cc214b4a9d3b7caa3f0454.

Per discussion and buildfarm, this depends on APIs that seem to not
be available on at least one platform (NetBSD).  Should be certainly
possible to rework to be optional on that platform if necessary but bit
late for that at this point.

Discussion: https://postgr.es/m/3286097.1680922218@sss.pgh.pa.us

Provide a way to ask the kernel to use O_DIRECT (or local equivalent)
where available for data and WAL files, to avoid or minimize kernel
caching.  This hurts performance currently and is not intended for end
users yet.  Later proposed work would introduce our own I/O clustering,
read-ahead, etc to replace the facilities the kernel disables with this
option.

The only user-visible change, if the developer-only GUC is not used, is
that this commit also removes the obscure logic that would activate
O_DIRECT for the WAL when wal_sync_method=open_[data]sync and
wal_level=minimal (which also requires max_wal_senders=0).  Those are
non-default and unlikely settings, and this behavior wasn't (correctly)
documented.  The same effect can be achieved with io_direct=wal.

Author: Thomas Munro <thomas.munro@gmail.com>
Author: Andres Freund <andres@anarazel.de>
Author: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Reviewed-by: Justin Pryzby <pryzby@telsasoft.com>
Reviewed-by: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Discussion: https://postgr.es/m/CA%2BhUKGK1X532hYqJ_MzFWt0n1zt8trz980D79WbjwnT-yYLZpg%40mail.gmail.com

Support GSSAPI/Kerberos credentials being delegated to the server by a
client.  With this, a user authenticating to PostgreSQL using Kerberos
(GSSAPI) credentials can choose to delegate their credentials to the
PostgreSQL server (which can choose to accept them, or not), allowing
the server to then use those delegated credentials to connect to
another service, such as with postgres_fdw or dblink or theoretically
any other service which is able to be authenticated using Kerberos.

Both postgres_fdw and dblink are changed to allow non-superuser
password-less connections but only when GSSAPI credentials have been
delegated to the server by the client and GSSAPI is used to
authenticate to the remote system.

Authors: Stephen Frost, Peifeng Qiu
Reviewed-By: David Christensen
Discussion: https://postgr.es/m/CO1PR05MB8023CC2CB575E0FAAD7DF4F8A8E29@CO1PR05MB8023.namprd05.prod.outlook.com