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PG-1059: Fix check-world failures #10

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@dutow dutow commented Sep 24, 2024

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dutow and others added 30 commits August 28, 2024 20:23
extension to see if custom features can be used
and allow extensions to override it
For now, it extends on `pread` and `pwrite` from/into segment files.
This is the minimum we need for full XLog encryption with pg_de.
PG-981: Renamed PERCONA_FORK to PERCONA_EXT
PG-847: exclude pg_tde* files from checksum validation
The failover slots ensure a seamless transition of a subscriber after the
standby is promoted. But the docs for it also explain the behavior of
asynchronous replication which can confuse the readers.

Reported-by: Masahiro Ikeda
Backpatch-through: 17
Discussion: https://postgr.es/m/OS3PR01MB6390B660F4198BB9745E0526B18B2@OS3PR01MB6390.jpnprd01.prod.outlook.com
This does not make sense.  It would write the output of the USING
clause into the converted column, which would violate the generation
expression.  This adds a check to error out if this is specified.

There was a test for this, but that test errored out for a different
reason, so it was not effective.

Reported-by: Jian He <jian.universality@gmail.com>
Reviewed-by: Yugo NAGATA <nagata@sraoss.co.jp>
Discussion: https://www.postgresql.org/message-id/flat/c7083982-69f4-4b14-8315-f9ddb20b9834%40eisentraut.org
If an ORDER BY item in SELECT is a bare identifier, the parser
first seeks it as an output column name of the SELECT (for SQL92
compatibility).  However, ruleutils.c is expecting the SQL99
interpretation where such a name is an input column name.  So it's
possible to produce an incorrect display of a view in the (admittedly
pretty ill-advised) case where some other column is renamed in the
SELECT output list to match an ORDER BY column.

This can be fixed by table-qualifying such names in the dumped
view text.  To avoid cluttering less-ill-advised queries, we'd
like to do so only when there's an actual name conflict.
That requires passing the current get_query_def call's resultDesc
parameter down to get_variable, so that it can determine what
the output column names are.  In hopes of reducing rather than
increasing notational clutter in ruleutils.c, I moved that value
into the deparse_context struct and removed it from the parameter
lists of get_query_def's other subroutines.

I made a few other cosmetic changes while at it:
* Likewise move the colNamesVisible parameter into deparse_context.
* Rename deparse_context's windowTList field to targetList,
since it's no longer used only in connection with WINDOW clauses.
* Replace the special_exprkind field with a bool inGroupBy,
since that was all it was being used for, and the apparent
flexibility of storing a ParseExprKind proved to be illusory.
(We need a separate varInOrderBy field to make this patch work.)
* Remove useless save/restore logic in get_select_query_def.

In principle, this bug is quite old.  However, it seems unreachable
before 1b4d280, because before that the presence of "new" and "old"
entries in a view's rangetable caused us to always table-qualify every
Var reference in dumped views.  Hence, back-patch to v16 where that
came in.

Per bug #18589 from Quynh Tran.

Discussion: https://postgr.es/m/18589-70091cb81db1a3f1@postgresql.org
Reported-by: Etsuro Fujita <etsuro.fujita@gmail.com>
Reported-by: m.zhilin@postgrespro.ru
Commit 2489d76 removed some logic from pullup_replace_vars()
that avoided wrapping a PlaceHolderVar around a pulled-up
subquery output expression if the expression could be proven
to go to NULL anyway (because it contained Vars or PHVs of the
pulled-up relation and did not contain non-strict constructs).
But removing that logic turns out to cause performance regressions
in some cases, because the extra PHV blocks subexpression folding,
and will do so even if outer-join reduction later turns it into a
no-op with no phnullingrels bits.  This can for example prevent
an expression from being matched to an index.

The reason for always adding a PHV was to ensure we had someplace
to put the varnullingrels marker bits of the Var being replaced.
However, it turns out we can optimize in exactly the same cases that
the previous code did, because we can instead attach the needed
varnullingrels bits to the contained Var(s)/PHV(s).

This is not a complete solution --- it would be even better if we
could remove PHVs after reducing them to no-ops.  It doesn't look
practical to back-patch such an improvement, but this change seems
safe and at least gets rid of the performance-regression cases.

Per complaint from Nikhil Raj.  Back-patch to v16 where the
problem appeared.

Discussion: https://postgr.es/m/CAG1ps1xvnTZceKK24OUfMKLPvDP2vjT-d+F2AOCWbw_v3KeEgg@mail.gmail.com
This test occasionally shows

+WARNING:  could not get result of cancel request due to timeout

which appears to be because the cancel request is sometimes unluckily
sent to the remote session between queries, and then it's ignored.

This patch tries to make that less probable in three ways:

1. Use a test query that does not involve remote estimates, so that
no EXPLAINs are sent.
2. Make sure that the remote session is ready-to-go (transaction
started, SET commands sent) before we start the timer.
3. Increase the statement_timeout to 100ms, to give the local
session enough time to plan and issue the query.

We might have to go higher than 100ms to make this adequately
stable in the buildfarm, but let's see how it goes.

Back-patch to v17 where this test was introduced.

Jelte Fennema-Nio and Tom Lane

Discussion: https://postgr.es/m/578934.1725045685@sss.pgh.pa.us
This change improves the description of the
restrict_nonsystem_relation_kind parameter in guc_table.c and the
documentation for better clarity.

Backpatch to 12, where this GUC parameter was introduced.

Reviewed-by: Peter Eisentraut
Discussion: https://postgr.es/m/6a96f1af-22b4-4a80-8161-1f26606b9ee2%40eisentraut.org
Backpatch-through: 12
The first test was sensitive to the insert LSN after setting up the
catalogs, which depended on environmental things like the locales on the
OS and usernames.  Switch to a new WAL file before the first test, as a
simple way to put every computer into the same state.

Back-patch to all supported releases.

Reported-by: Anton Voloshin <a.voloshin@postgrespro.ru>
Reported-by: Nathan Bossart <nathandbossart@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Nathan Bossart <nathandbossart@gmail.com>
Discussion: https://postgr.es/m/b26aeac2-cb6d-4633-a7ea-945baae83dcf%40postgrespro.ru
Commit b5a9b18 introduced block streaming infrastructure with a special
fast path for all-cached scans, and commit b7b0f3f connected the
infrastructure up to sequential scans.  One of the fast path
micro-optimizations had an unintended consequence: it interfered with
parallel sequential scan's block range allocator (from commit 56788d2),
which has its own ramp-up and ramp-down algorithm when handing out
groups of pages to workers.  A scan of an all-cached table could give
extra blocks to one worker, when others had finished.  In some plans
(probably already very bad plans, such as the one reported by
Alexander), the unfairness could be magnified.

An internal buffer of 16 block numbers is removed, keeping just a single
block buffer for technical reasons.

Back-patch to 17.

Reported-by: Alexander Lakhin <exclusion@gmail.com>
Discussion: https://postgr.es/m/63a63690-dd92-c809-0b47-af05459e95d1%40gmail.com
Source-Git-URL: https://git.postgresql.org/git/pgtranslation/messages.git
Source-Git-Hash: d0110df9f34c2d32cb2652d4477c3135dabe84f7
fixup for 2e6a804

Reported-by: Nazir Bilal Yavuz <byavuz81@gmail.com>
/usr/bin/msgfmt: po/fr.po: warning: PO file header fuzzy
                           warning: older versions of msgfmt will give an error on this

Apparently, not all versions of msgfmt produce this.  Quick fix for
now, more to be researched later.
michaelpq and others added 20 commits September 6, 2024 17:21
This is confusing, as it exports twice the same variable.  Oversight in
6782709 that has spread in more places afterwards.

Reported-by: Alvaro Herrera, Tom Lane
Discussion: https://postgr.es/m/202408201630.mn6vbohjh7hh@alvherre.pgsql
Backpatch-through: 17
These tests depend on the test module injection_points to be installed,
but it may not be available as the contents of src/test/modules/ are not
installed by default.

This commit adds a workaround based on a scan of pg_available_extensions
to check if the extension is available, skipping the test if it is not.
This allows installcheck to work transparently.

There are more tests impacted by this problem on HEAD, but for now this
addresses only the tests that exist on HEAD and v17 as the release is
close by.

Reported-by: Maxim Orlov
Discussion: https://postgr.es/m/CACG=ezZkoT-pFz6a9XnyToiuR-Wg8fGELqHLoyBodr+2h-77qA@mail.gmail.com
Backpatch-through: 17
This term was using an inconsistent casing between the code and the
documentation, using "CommitTsSLRU" in wait_event_names.txt and
"CommitTSSLRU" in the code.

Let's update the term in the code to reflect what's in the
documentation, "CommitTs" being more commonly used, so as
pg_stat_activity shows the same term as the documentation.

Oversight in 53c2a97.

Author: Alexander Lakhin
Discussion: https://postgr.es/m/f7e514cf-2446-21f1-a5d2-8c089a6e2168@gmail.com
Backpatch-through: 17
Since commit 2549f06, we reject an identifier immediately following
a numeric literal (without separating whitespace), because that risks
ambiguity with hex/octal/binary integers.  However, that patch used
token patterns like "{integer}{ident_start}", which is problematic
because {ident_start} matches only a single byte.  If the first
character after the integer is a multibyte character, this ends up
with flex reporting an error message that includes a partial multibyte
character.  That can cause assorted bad-encoding problems downstream,
both in the report to the client and in the postmaster log file.

To fix, use {identifier} not {ident_start} in the "junk" token
patterns, so that they will match complete multibyte characters.
This seems generally better user experience quite aside from the
encoding problem: for "123abc" the error message will now say that
the error appeared at or near "123abc" instead of "123a".

While at it, add some commentary about why these patterns exist
and how they work.

Report and patch by Karina Litskevich; review by Pavel Borisov.
Back-patch to v15 where the problem came in.

Discussion: https://postgr.es/m/CACiT8iZ_diop=0zJ7zuY3BXegJpkKK1Av-PU7xh0EDYHsa5+=g@mail.gmail.com
The updated comment provides more helpful guidance by mentioning that
escontext should be set when soft error handling is needed.

Reported-by: Jian He <jian.universality@gmail.com>
Discussion: https://postgr.es/m/CACJufxEo4sUjKCYtda0_qt9tazqqKPmF1cqhW9KBOUeJFqQd2g@mail.gmail.com
Backpatch-through: 17
The deparsing code in get_json_expr_options() unnecessarily emitted
the default column-specific ON ERROR / EMPTY behavior when the
top-level ON ERROR behavior in JSON_TABLE was set to ERROR. Fix that
by not overriding the column-specific default, determined based on
the column's JsonExprOp in get_json_table_columns(), with
JSON_BEHAVIOR_ERROR when that is the top-level ON ERROR behavior.

Note that this only removes redundancy; the current deparsing output
is not incorrect, just redundant.

Reviewed-by: Jian He <jian.universality@gmail.com>
Discussion: https://postgr.es/m/CACJufxEo4sUjKCYtda0_qt9tazqqKPmF1cqhW9KBOUeJFqQd2g@mail.gmail.com
Backpatch-through: 17
Use EMPTY ARRAY instead of EMPTY.

This change does not affect the runtime behavior of JSON_TABLE(),
which continues to return an empty relation ON ERROR. It only alters
whether the default ON ERROR behavior is shown in the deparsed output.

Reported-by: Jian He <jian.universality@gmail.com>
Discussion: https://postgr.es/m/CACJufxEo4sUjKCYtda0_qt9tazqqKPmF1cqhW9KBOUeJFqQd2g@mail.gmail.com
Backpatch-through: 17
When the ON ERROR / ON EMPTY behavior is to return NULL, returning
NULL directly from ExecEvalJsonExprPath() suffices. Therefore, there's
no need to create separate steps to check the error/empty flag or
those to evaluate the the constant NULL expression.  This speeds up
common cases because the default ON ERROR / ON EMPTY behavior for
JSON_QUERY() and JSON_VALUE() is to return NULL.  However, these steps
are necessary if the RETURNING type is a domain, as constraints on the
domain may need to be checked.

Reported-by: Jian He <jian.universality@gmail.com>
Author: Jian He <jian.universality@gmail.com>
Author: Amit Langote <amitlangote09@gmail.com>
Discussion: https://postgr.es/m/CACJufxEo4sUjKCYtda0_qt9tazqqKPmF1cqhW9KBOUeJFqQd2g@mail.gmail.com
Backpatch-through: 17
Reverts c88ce38, 5067c23, and  e4e2797, because a few BF
animals didn't like one or all of them.
The deparsing code in get_json_expr_options() unnecessarily emitted
the default column-specific ON ERROR / EMPTY behavior when the
top-level ON ERROR behavior in JSON_TABLE was set to ERROR. Fix that
by not overriding the column-specific default, determined based on
the column's JsonExprOp in get_json_table_columns(), with
JSON_BEHAVIOR_ERROR when that is the top-level ON ERROR behavior.

Note that this only removes redundancy; the current deparsing output
is not incorrect, just redundant.

Reviewed-by: Jian He <jian.universality@gmail.com>
Discussion: https://postgr.es/m/CACJufxEo4sUjKCYtda0_qt9tazqqKPmF1cqhW9KBOUeJFqQd2g@mail.gmail.com
Backpatch-through: 17
Use EMPTY ARRAY instead of EMPTY.

This change does not affect the runtime behavior of JSON_TABLE(),
which continues to return an empty relation ON ERROR. It only alters
whether the default ON ERROR behavior is shown in the deparsed output.

Reported-by: Jian He <jian.universality@gmail.com>
Discussion: https://postgr.es/m/CACJufxEo4sUjKCYtda0_qt9tazqqKPmF1cqhW9KBOUeJFqQd2g@mail.gmail.com
Backpatch-through: 17
Updated product name from PostgreSQL to Percona Server for PostgreSQL
and incremented the version number from 17rc1 to 17rc1.1.
This commit adds two test runners which build Postgres with make
and meson, and run the basic regression tests.

Tests are executed for every PR, and also every day using the
latest pg_tde code.
This way the build scripts are aware of its value, and we can use
it to add tests specifically to tde_heap, or other percona features.
PERCONA_EXT is now a configuration option, not hardcoded
PG-1008: Change product name and version number
@Naeem-Akhter
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I guess, there would be no need of changes after we decided in the meeting, that we won't change the existing --version string, but will add another flag/identifier as '--with-extra-version' to identify Percona Build and package number.

Your thoughts @dutow

@dutow dutow closed this Sep 30, 2024
dutow pushed a commit that referenced this pull request Nov 14, 2024
1. TruncateMultiXact() performs the SLRU truncations in a critical
section. Deleting the SLRU segments calls ForwardSyncRequest(), which
will try to compact the request queue if it's full
(CompactCheckpointerRequestQueue()). That in turn allocates memory,
which is not allowed in a critical section. Backtrace:

    TRAP: failed Assert("CritSectionCount == 0 || (context)->allowInCritSection"), File: "../src/backend/utils/mmgr/mcxt.c", Line: 1353, PID: 920981
    postgres: autovacuum worker template0(ExceptionalCondition+0x6e)[0x560a501e866e]
    postgres: autovacuum worker template0(+0x5dce3d)[0x560a50217e3d]
    postgres: autovacuum worker template0(ForwardSyncRequest+0x8e)[0x560a4ffec95e]
    postgres: autovacuum worker template0(RegisterSyncRequest+0x2b)[0x560a50091eeb]
    postgres: autovacuum worker template0(+0x187b0a)[0x560a4fdc2b0a]
    postgres: autovacuum worker template0(SlruDeleteSegment+0x101)[0x560a4fdc2ab1]
    postgres: autovacuum worker template0(TruncateMultiXact+0x2fb)[0x560a4fdbde1b]
    postgres: autovacuum worker template0(vac_update_datfrozenxid+0x4b3)[0x560a4febd2f3]
    postgres: autovacuum worker template0(+0x3adf66)[0x560a4ffe8f66]
    postgres: autovacuum worker template0(AutoVacWorkerMain+0x3ed)[0x560a4ffe7c2d]
    postgres: autovacuum worker template0(+0x3b1ead)[0x560a4ffecead]
    postgres: autovacuum worker template0(+0x3b620e)[0x560a4fff120e]
    postgres: autovacuum worker template0(+0x3b3fbb)[0x560a4ffeefbb]
    postgres: autovacuum worker template0(+0x2f724e)[0x560a4ff3224e]
    /lib/x86_64-linux-gnu/libc.so.6(+0x27c8a)[0x7f62cc642c8a]
    /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0x85)[0x7f62cc642d45]
    postgres: autovacuum worker template0(_start+0x21)[0x560a4fd16f31]

To fix, bail out in CompactCheckpointerRequestQueue() without doing
anything, if it's called in a critical section. That covers the above
call path, as well as any other similar cases where
RegisterSyncRequest might be called in a critical section.

2. After fixing that, another problem became apparent: Autovacuum
process doing that truncation can deadlock with the checkpointer
process. TruncateMultiXact() sets "MyProc->delayChkptFlags |=
DELAY_CHKPT_START". If the sync request queue is full and cannot be
compacted, the process will repeatedly sleep and retry, until there is
room in the queue. However, if the checkpointer is trying to start a
checkpoint at the same time, and is waiting for the DELAY_CHKPT_START
processes to finish, the queue will never shrink.

More concretely, the autovacuum process is stuck here:

    #0  0x00007fc934926dc3 in epoll_wait () from /lib/x86_64-linux-gnu/libc.so.6
    #1  0x000056220b24348b in WaitEventSetWaitBlock (set=0x56220c2e4b50, occurred_events=0x7ffe7856d040, nevents=1, cur_timeout=<optimized out>) at ../src/backend/storage/ipc/latch.c:1570
    #2  WaitEventSetWait (set=0x56220c2e4b50, timeout=timeout@entry=10, occurred_events=<optimized out>, occurred_events@entry=0x7ffe7856d040, nevents=nevents@entry=1,
        wait_event_info=wait_event_info@entry=150994949) at ../src/backend/storage/ipc/latch.c:1516
    #3  0x000056220b243224 in WaitLatch (latch=<optimized out>, latch@entry=0x0, wakeEvents=wakeEvents@entry=40, timeout=timeout@entry=10, wait_event_info=wait_event_info@entry=150994949)
        at ../src/backend/storage/ipc/latch.c:538
    #4  0x000056220b26cf46 in RegisterSyncRequest (ftag=ftag@entry=0x7ffe7856d0a0, type=type@entry=SYNC_FORGET_REQUEST, retryOnError=true) at ../src/backend/storage/sync/sync.c:614
    #5  0x000056220af9db0a in SlruInternalDeleteSegment (ctl=ctl@entry=0x56220b7beb60 <MultiXactMemberCtlData>, segno=segno@entry=11350) at ../src/backend/access/transam/slru.c:1495
    #6  0x000056220af9dab1 in SlruDeleteSegment (ctl=ctl@entry=0x56220b7beb60 <MultiXactMemberCtlData>, segno=segno@entry=11350) at ../src/backend/access/transam/slru.c:1566
    #7  0x000056220af98e1b in PerformMembersTruncation (oldestOffset=<optimized out>, newOldestOffset=<optimized out>) at ../src/backend/access/transam/multixact.c:3006
    #8  TruncateMultiXact (newOldestMulti=newOldestMulti@entry=3221225472, newOldestMultiDB=newOldestMultiDB@entry=4) at ../src/backend/access/transam/multixact.c:3201
    #9  0x000056220b098303 in vac_truncate_clog (frozenXID=749, minMulti=<optimized out>, lastSaneFrozenXid=749, lastSaneMinMulti=3221225472) at ../src/backend/commands/vacuum.c:1917
    #10 vac_update_datfrozenxid () at ../src/backend/commands/vacuum.c:1760
    #11 0x000056220b1c3f76 in do_autovacuum () at ../src/backend/postmaster/autovacuum.c:2550
    #12 0x000056220b1c2c3d in AutoVacWorkerMain (startup_data=<optimized out>, startup_data_len=<optimized out>) at ../src/backend/postmaster/autovacuum.c:1569

and the checkpointer is stuck here:

    #0  0x00007fc9348ebf93 in clock_nanosleep () from /lib/x86_64-linux-gnu/libc.so.6
    #1  0x00007fc9348fe353 in nanosleep () from /lib/x86_64-linux-gnu/libc.so.6
    #2  0x000056220b40ecb4 in pg_usleep (microsec=microsec@entry=10000) at ../src/port/pgsleep.c:50
    #3  0x000056220afb43c3 in CreateCheckPoint (flags=flags@entry=108) at ../src/backend/access/transam/xlog.c:7098
    #4  0x000056220b1c6e86 in CheckpointerMain (startup_data=<optimized out>, startup_data_len=<optimized out>) at ../src/backend/postmaster/checkpointer.c:464

To fix, add AbsorbSyncRequests() to the loops where the checkpointer
waits for DELAY_CHKPT_START or DELAY_CHKPT_COMPLETE operations to
finish.

Backpatch to v14. Before that, SLRU deletion didn't call
RegisterSyncRequest, which avoided this failure. I'm not sure if there
are other similar scenarios on older versions, but we haven't had
any such reports.

Discussion: https://www.postgresql.org/message-id/ccc66933-31c1-4f6a-bf4b-45fef0d4f22e@iki.fi
dutow pushed a commit that referenced this pull request Nov 14, 2024
1. TruncateMultiXact() performs the SLRU truncations in a critical
section. Deleting the SLRU segments calls ForwardSyncRequest(), which
will try to compact the request queue if it's full
(CompactCheckpointerRequestQueue()). That in turn allocates memory,
which is not allowed in a critical section. Backtrace:

    TRAP: failed Assert("CritSectionCount == 0 || (context)->allowInCritSection"), File: "../src/backend/utils/mmgr/mcxt.c", Line: 1353, PID: 920981
    postgres: autovacuum worker template0(ExceptionalCondition+0x6e)[0x560a501e866e]
    postgres: autovacuum worker template0(+0x5dce3d)[0x560a50217e3d]
    postgres: autovacuum worker template0(ForwardSyncRequest+0x8e)[0x560a4ffec95e]
    postgres: autovacuum worker template0(RegisterSyncRequest+0x2b)[0x560a50091eeb]
    postgres: autovacuum worker template0(+0x187b0a)[0x560a4fdc2b0a]
    postgres: autovacuum worker template0(SlruDeleteSegment+0x101)[0x560a4fdc2ab1]
    postgres: autovacuum worker template0(TruncateMultiXact+0x2fb)[0x560a4fdbde1b]
    postgres: autovacuum worker template0(vac_update_datfrozenxid+0x4b3)[0x560a4febd2f3]
    postgres: autovacuum worker template0(+0x3adf66)[0x560a4ffe8f66]
    postgres: autovacuum worker template0(AutoVacWorkerMain+0x3ed)[0x560a4ffe7c2d]
    postgres: autovacuum worker template0(+0x3b1ead)[0x560a4ffecead]
    postgres: autovacuum worker template0(+0x3b620e)[0x560a4fff120e]
    postgres: autovacuum worker template0(+0x3b3fbb)[0x560a4ffeefbb]
    postgres: autovacuum worker template0(+0x2f724e)[0x560a4ff3224e]
    /lib/x86_64-linux-gnu/libc.so.6(+0x27c8a)[0x7f62cc642c8a]
    /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0x85)[0x7f62cc642d45]
    postgres: autovacuum worker template0(_start+0x21)[0x560a4fd16f31]

To fix, bail out in CompactCheckpointerRequestQueue() without doing
anything, if it's called in a critical section. That covers the above
call path, as well as any other similar cases where
RegisterSyncRequest might be called in a critical section.

2. After fixing that, another problem became apparent: Autovacuum
process doing that truncation can deadlock with the checkpointer
process. TruncateMultiXact() sets "MyProc->delayChkptFlags |=
DELAY_CHKPT_START". If the sync request queue is full and cannot be
compacted, the process will repeatedly sleep and retry, until there is
room in the queue. However, if the checkpointer is trying to start a
checkpoint at the same time, and is waiting for the DELAY_CHKPT_START
processes to finish, the queue will never shrink.

More concretely, the autovacuum process is stuck here:

    #0  0x00007fc934926dc3 in epoll_wait () from /lib/x86_64-linux-gnu/libc.so.6
    #1  0x000056220b24348b in WaitEventSetWaitBlock (set=0x56220c2e4b50, occurred_events=0x7ffe7856d040, nevents=1, cur_timeout=<optimized out>) at ../src/backend/storage/ipc/latch.c:1570
    #2  WaitEventSetWait (set=0x56220c2e4b50, timeout=timeout@entry=10, occurred_events=<optimized out>, occurred_events@entry=0x7ffe7856d040, nevents=nevents@entry=1,
        wait_event_info=wait_event_info@entry=150994949) at ../src/backend/storage/ipc/latch.c:1516
    #3  0x000056220b243224 in WaitLatch (latch=<optimized out>, latch@entry=0x0, wakeEvents=wakeEvents@entry=40, timeout=timeout@entry=10, wait_event_info=wait_event_info@entry=150994949)
        at ../src/backend/storage/ipc/latch.c:538
    #4  0x000056220b26cf46 in RegisterSyncRequest (ftag=ftag@entry=0x7ffe7856d0a0, type=type@entry=SYNC_FORGET_REQUEST, retryOnError=true) at ../src/backend/storage/sync/sync.c:614
    #5  0x000056220af9db0a in SlruInternalDeleteSegment (ctl=ctl@entry=0x56220b7beb60 <MultiXactMemberCtlData>, segno=segno@entry=11350) at ../src/backend/access/transam/slru.c:1495
    #6  0x000056220af9dab1 in SlruDeleteSegment (ctl=ctl@entry=0x56220b7beb60 <MultiXactMemberCtlData>, segno=segno@entry=11350) at ../src/backend/access/transam/slru.c:1566
    #7  0x000056220af98e1b in PerformMembersTruncation (oldestOffset=<optimized out>, newOldestOffset=<optimized out>) at ../src/backend/access/transam/multixact.c:3006
    #8  TruncateMultiXact (newOldestMulti=newOldestMulti@entry=3221225472, newOldestMultiDB=newOldestMultiDB@entry=4) at ../src/backend/access/transam/multixact.c:3201
    #9  0x000056220b098303 in vac_truncate_clog (frozenXID=749, minMulti=<optimized out>, lastSaneFrozenXid=749, lastSaneMinMulti=3221225472) at ../src/backend/commands/vacuum.c:1917
    #10 vac_update_datfrozenxid () at ../src/backend/commands/vacuum.c:1760
    #11 0x000056220b1c3f76 in do_autovacuum () at ../src/backend/postmaster/autovacuum.c:2550
    #12 0x000056220b1c2c3d in AutoVacWorkerMain (startup_data=<optimized out>, startup_data_len=<optimized out>) at ../src/backend/postmaster/autovacuum.c:1569

and the checkpointer is stuck here:

    #0  0x00007fc9348ebf93 in clock_nanosleep () from /lib/x86_64-linux-gnu/libc.so.6
    #1  0x00007fc9348fe353 in nanosleep () from /lib/x86_64-linux-gnu/libc.so.6
    #2  0x000056220b40ecb4 in pg_usleep (microsec=microsec@entry=10000) at ../src/port/pgsleep.c:50
    #3  0x000056220afb43c3 in CreateCheckPoint (flags=flags@entry=108) at ../src/backend/access/transam/xlog.c:7098
    #4  0x000056220b1c6e86 in CheckpointerMain (startup_data=<optimized out>, startup_data_len=<optimized out>) at ../src/backend/postmaster/checkpointer.c:464

To fix, add AbsorbSyncRequests() to the loops where the checkpointer
waits for DELAY_CHKPT_START or DELAY_CHKPT_COMPLETE operations to
finish.

Backpatch to v14. Before that, SLRU deletion didn't call
RegisterSyncRequest, which avoided this failure. I'm not sure if there
are other similar scenarios on older versions, but we haven't had
any such reports.

Discussion: https://www.postgresql.org/message-id/ccc66933-31c1-4f6a-bf4b-45fef0d4f22e@iki.fi
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