Thread

Commits

  1. Fix outdated comment on MainLWLockArray

  2. Fix RequestNamedLWLockTranche in single-user mode

  3. Minor comment fixes to yesterday's LWLock tranche refactoring

  4. Move ShmemIndexLock into ShmemAllocator

  5. Use ShmemInitStruct to allocate lwlock.c's shared memory

  6. Use a separate spinlock to protect LWLockTranches

  7. Refactor how user-defined LWLock tranches are stored in shmem

  8. Rename MAX_NAMED_TRANCHES to MAX_USER_DEFINED_TRANCHES

  9. Fix re-initialization of LWLock-related shared memory.

  1. Clean up NamedLWLockTranche stuff

    Heikki Linnakangas <hlinnaka@iki.fi> — 2026-03-26T12:16:52Z

    While working on the new shmem allocation functions, I looked at how the 
    NamedLWLockTranche stuff works now in lwlock.c, and I have to say it's a 
    bit of a mess.
    
    What is a "named tranche"? It usually means tranches requested with 
    RequestNamedLWLockTranche() at postmaster startup. But all tranches have 
    a name. LWLockTrancheNames includes all user-defined tranches, also ones 
    assigned with LWLockNewTrancheId(), and MAX_NAMED_TRANCHES is the 
    maximum for all of them.
    
    At postmaster startup, NamedLWLockTrancheRequests points to a 
    backend-private array. But after startup, and always in backends, it 
    points to a copy in shared memory and 
    LocalNamedLWLockTrancheRequestArray is used to hold the original. It 
    took me a while to realize that NamedLWLockTrancheRequests in shared 
    memory is *not* updated when you call LWLockNewTrancheId(), it only 
    holds the requests made with RequestNamedLWLockTranche() before startup.
    
    I propose the attached refactorings to make this less confusing. See 
    commit messages for details.
    
    - Heikki
    
  2. Re: Clean up NamedLWLockTranche stuff

    Nathan Bossart <nathandbossart@gmail.com> — 2026-03-26T14:37:28Z

    On Thu, Mar 26, 2026 at 02:16:52PM +0200, Heikki Linnakangas wrote:
    > At postmaster startup, NamedLWLockTrancheRequests points to a
    > backend-private array. But after startup, and always in backends, it points
    > to a copy in shared memory and LocalNamedLWLockTrancheRequestArray is used
    > to hold the original. It took me a while to realize that
    > NamedLWLockTrancheRequests in shared memory is *not* updated when you call
    > LWLockNewTrancheId(), it only holds the requests made with
    > RequestNamedLWLockTranche() before startup.
    
    Right.  LocalNamedLWLockTrancheRequestArray is needed so that we can
    re-initialize shared memory after a crash.  See commit c3cc2ab87d.
    
    > I propose the attached refactorings to make this less confusing. See commit
    > messages for details.
    
    Thanks for doing this, Heikki.  I agree that we ought to make this stuff
    cleaner.  I've asked Sami Imseih, who worked on LWLocks with me last year,
    to look at this patch set, too.
    
    > Subject: [PATCH v1 1/5] Rename MAX_NAMED_TRANCHES to MAX_USER_DEFINED_TRANCHES
    
    Seems fine to me.
    
    0002:
    
    > +	foreach(lc, NamedLWLockTrancheRequests)
    
    nitpick: These foreach loops seem like good opportunities to use
    foreach_ptr.
    
    The comment atop NumLWLocksForNamedTranches might benefit from mentioning
    RequestNamedLWLockTranche() and the fact that it only works in the
    postmaster.  Perhaps an assertion is warranted, too.
    
    +	SpinLockAcquire(ShmemLock);
    +	LocalNumUserDefinedTranches = LWLockTranches->num_user_defined;
    +	SpinLockRelease(ShmemLock);
    
    Not critical, but it might be worth making num_user_defined an atomic.
    
    Overall, 0002 looks reasonable to me upon a first read-through.
    
    > Subject: [PATCH v1 3/5] Use a separate spinlock to protect LWLockTranches
    
    Seems fine to me.
    
    0004:
    
    > +++ b/src/backend/storage/ipc/shmem.c
    > @@ -379,7 +379,8 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr)
    >  
    >  	Assert(ShmemIndex != NULL);
    >  
    > -	LWLockAcquire(ShmemIndexLock, LW_EXCLUSIVE);
    > +	if (IsUnderPostmaster)
    > +		LWLockAcquire(ShmemIndexLock, LW_EXCLUSIVE);
    
    Am I understanding that we assume ShmemInitStruct() is only called by the
    postmaster when there are no other backends yet?
    
    0005:
    
    > -	if (IsUnderPostmaster)
    > -		LWLockAcquire(ShmemIndexLock, LW_EXCLUSIVE);
    > +	LWLockAcquire(ShmemIndexLock, LW_EXCLUSIVE);
    
    Oh, this reverts many of these changes from 0004.  Maybe the patches could
    be reordered to avoid this?
    
    -- 
    nathan
    
    
    
    
  3. Re: Clean up NamedLWLockTranche stuff

    Heikki Linnakangas <hlinnaka@iki.fi> — 2026-03-26T15:21:58Z

    On 26/03/2026 16:37, Nathan Bossart wrote:
    > On Thu, Mar 26, 2026 at 02:16:52PM +0200, Heikki Linnakangas wrote:
    >> 0002:
    >> 
    >> +	foreach(lc, NamedLWLockTrancheRequests)
    > 
    > nitpick: These foreach loops seem like good opportunities to use
    > foreach_ptr.
    > 
    > The comment atop NumLWLocksForNamedTranches might benefit from mentioning
    > RequestNamedLWLockTranche() and the fact that it only works in the
    > postmaster.  Perhaps an assertion is warranted, too.
    
    There's already this check in RequestNamedLWLockTranche():
    
         if (!process_shmem_requests_in_progress)
             elog(FATAL, "cannot request additional LWLocks outside 
    shmem_request_hook");
    
    shmem_request_hooks are only called early at postmaster startup.
    
    > +	SpinLockAcquire(ShmemLock);
    > +	LocalNumUserDefinedTranches = LWLockTranches->num_user_defined;
    > +	SpinLockRelease(ShmemLock);
    > 
    > Not critical, but it might be worth making num_user_defined an atomic.
    
    Yeah I considered that. The lock is still needed in 
    LWLockNewTrancheId(), though, to prevent two concurrent 
    LWLockNewTrancheId() calls from running concurrently. Using an atomic 
    would allow the extra optimization of reading the value without 
    acquiring spinlock, but it seems more clear to have a clear-cut rule 
    that you must always hold the spinlock whenever accessing the field.
    
    > 0004:
    > 
    >> +++ b/src/backend/storage/ipc/shmem.c
    >> @@ -379,7 +379,8 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr)
    >>   
    >>   	Assert(ShmemIndex != NULL);
    >>   
    >> -	LWLockAcquire(ShmemIndexLock, LW_EXCLUSIVE);
    >> +	if (IsUnderPostmaster)
    >> +		LWLockAcquire(ShmemIndexLock, LW_EXCLUSIVE);
    > 
    > Am I understanding that we assume ShmemInitStruct() is only called by the
    > postmaster when there are no other backends yet?
    
    Yeah. LWLockAcquire has this:
    
         /*
          * We can't wait if we haven't got a PGPROC.  This should only occur
          * during bootstrap or shared memory initialization.  Put an Assert 
    here
          * to catch unsafe coding practices.
          */
         Assert(!(proc == NULL && IsUnderPostmaster));
    
    To be honest I didn't realize we tolerate that, calling LWLockAcquire in 
    postmaster, until I started to work on this. It might be worth having 
    some extra sanity checks here, to e.g. to throw an error if 
    LWLockAcquire is called from postmaster after startup. But this isn't new.
    
    > 0005:
    > 
    >> -	if (IsUnderPostmaster)
    >> -		LWLockAcquire(ShmemIndexLock, LW_EXCLUSIVE);
    >> +	LWLockAcquire(ShmemIndexLock, LW_EXCLUSIVE);
    > 
    > Oh, this reverts many of these changes from 0004.  Maybe the patches could
    > be reordered to avoid this?
    
    Makes sense.
    
    Thanks for the review!
    
    - Heikki
    
    
    
    
    
  4. Re: Clean up NamedLWLockTranche stuff

    Sami Imseih <samimseih@gmail.com> — 2026-03-26T16:34:32Z

    Hi,
    
    Thanks for the patches!
    
    > I propose the attached refactorings to make this less confusing. See
    > commit messages for details.
    
    I only took a look at 0001 so far, and I do agree with this statement
    in the commit message:
    
    "The "user defined" term was already used in LWTRANCHE_FIRST_USER_DEFINED,
    so let's standardize on that to mean tranches allocated with either
    RequestNamedLWLockTranche() or LWLockNewTrancheId()."
    
    I do wonder if 0001 is going far enough though.
    
    Instead of just standardizing that "user defined" could mean tranches allocated
    with RequestNamedLWLockTranche() or LWLockNewTrancheId(), how about we also
    rename these APIs to reflect that as well? This way we remove all concept of
    "named tranche" which is what it sounds like to me you are proposing.
    
    rename RequestNamedLWLockTranche() to RequestUserDefinedLWLockTranche()
    and LWLockNewTrancheId() to RegisterUserDefinedLWLockTranche()
    
    RequestNamedLWLockTranche() requests the lwlock at shmem_request time,
    which is later registered via LWLockNewTrancheId() when lwlocks are
    initialized by the postmaster.
    
    Also, the name LWLockNewTrancheId() is selling what this function does
    too short.
    It does return a new tranche ID, but it also takes in a user-defined tranche
    name and copies ("registers") that name into LWLockTrancheNames.
    
    v19 is already changing the signature of LWLockNewTrancheId(), so maybe
    improving the names of these APIs makes sense to do.
    
    --
    Sami Imseih
    Amazon Web Services (AWS)
    
    
    
    
  5. Re: Clean up NamedLWLockTranche stuff

    Heikki Linnakangas <hlinnaka@iki.fi> — 2026-03-26T16:57:51Z

    Thanks!
    
    On 26/03/2026 18:34, Sami Imseih wrote:
    >> I propose the attached refactorings to make this less confusing. See
    >> commit messages for details.
    > 
    > I only took a look at 0001 so far, and I do agree with this statement
    > in the commit message:
    > 
    > "The "user defined" term was already used in LWTRANCHE_FIRST_USER_DEFINED,
    > so let's standardize on that to mean tranches allocated with either
    > RequestNamedLWLockTranche() or LWLockNewTrancheId()."
    > 
    > I do wonder if 0001 is going far enough though.
    > 
    > Instead of just standardizing that "user defined" could mean tranches allocated
    > with RequestNamedLWLockTranche() or LWLockNewTrancheId(), how about we also
    > rename these APIs to reflect that as well? This way we remove all concept of
    > "named tranche" which is what it sounds like to me you are proposing.
    > 
    > rename RequestNamedLWLockTranche() to RequestUserDefinedLWLockTranche()
    > and LWLockNewTrancheId() to RegisterUserDefinedLWLockTranche()
    
    I'd rather not change RequestNamedLWLockTranche(), because I think 
    LWLockNewTrancheId() is better and should be used in new code. I 
    consider RequestNamedLWLockTranche() to be a legacy function, for 
    backwards compatibility.
    
    > RequestNamedLWLockTranche() requests the lwlock at shmem_request time,
    > which is later registered via LWLockNewTrancheId() when lwlocks are
    > initialized by the postmaster.
    > 
    > Also, the name LWLockNewTrancheId() is selling what this function does
    > too short.
    > It does return a new tranche ID, but it also takes in a user-defined tranche
    > name and copies ("registers") that name into LWLockTrancheNames.
    > 
    > v19 is already changing the signature of LWLockNewTrancheId(), so maybe
    > improving the names of these APIs makes sense to do.
    
    Oh, I didn't realize we changed the LWLockNewTrancheId() signature! 
    Yeah, if we're changing it anyway, we might as well rename it. I'm not 
    sure if I like RegisterUserDefinedLWLockTranche() better, but let's 
    think it through.
    
    - Heikki
    
    
    
    
    
  6. Re: Clean up NamedLWLockTranche stuff

    Heikki Linnakangas <hlinnaka@iki.fi> — 2026-03-26T22:03:15Z

    On 26/03/2026 18:57, Heikki Linnakangas wrote:
    > Thanks!
    > 
    > On 26/03/2026 18:34, Sami Imseih wrote:
    >>> I propose the attached refactorings to make this less confusing. See
    >>> commit messages for details.
    >>
    >> I only took a look at 0001 so far, and I do agree with this statement
    >> in the commit message:
    
    I committed these now, but I'm all ears if you still have comments on 
    the rest of the patches.
    
    - Heikki
    
    
    
    
    
  7. Re: Clean up NamedLWLockTranche stuff

    Sami Imseih <samimseih@gmail.com> — 2026-03-27T03:57:44Z

    Hi,
    
    > > Thanks!
    > >
    > > On 26/03/2026 18:34, Sami Imseih wrote:
    > >>> I propose the attached refactorings to make this less confusing. See
    > >>> commit messages for details.
    > >>
    > >> I only took a look at 0001 so far, and I do agree with this statement
    > >> in the commit message:
    >
    > I committed these now, but I'm all ears if you still have comments on
    > the rest of the patches.
    
    Sorry for the delay. I see you committed the rest. The only issue I found
    is with d6eba30
    
    +/* backend-local copy of NamedLWLockTranches->num_user_defined */
    +static int  LocalNumUserDefinedTranches;
    
    The comment here should reference "LWLockTranches->num_user_defined "
    instead.
    
    >> rename RequestNamedLWLockTranche() to RequestUserDefinedLWLockTranche()
    >> and LWLockNewTrancheId() to RegisterUserDefinedLWLockTranche()
    
    > I'd rather not change RequestNamedLWLockTranche(), because I think
    > LWLockNewTrancheId() is better and should be used in new code.
    
    That's fair.
    
    >> v19 is already changing the signature of LWLockNewTrancheId(), so maybe
    >> improving the names of these APIs makes sense to do.
    
    > Oh, I didn't realize we changed the LWLockNewTrancheId() signature!
    > Yeah, if we're changing it anyway, we might as well rename it. I'm not
    > sure if I like RegisterUserDefinedLWLockTranche() better, but let's
    > think it through.
    
    Maybe, RegisterNewLWLockTrancheId() could be more meaningful?
    
    Also, there are a few places in lwlock.c where "named tranches" is mentioned.
    Maybe we should just say "user-defined tranches" instead?
    
    --
    Sami Imseih
    Amazon Web Services (AWS)
    
    
    
    
  8. Re: Clean up NamedLWLockTranche stuff

    Sami Imseih <samimseih@gmail.com> — 2026-03-27T04:49:11Z

    > +/* backend-local copy of NamedLWLockTranches->num_user_defined */
    > +static int  LocalNumUserDefinedTranches;
    
    > The comment here should reference "LWLockTranches->num_user_defined "
    > instead.
    
    > Also, there are a few places in lwlock.c where "named tranches" is mentioned.
    > Maybe we should just say "user-defined tranches" instead?
    
    Like the attached.
    
    --
    Sami
    
  9. Re: Clean up NamedLWLockTranche stuff

    Heikki Linnakangas <hlinnaka@iki.fi> — 2026-03-27T09:45:56Z

    On 27/03/2026 06:49, Sami Imseih wrote:
    >> +/* backend-local copy of NamedLWLockTranches->num_user_defined */
    >> +static int  LocalNumUserDefinedTranches;
    > 
    >> The comment here should reference "LWLockTranches->num_user_defined "
    >> instead.
    > 
    >> Also, there are a few places in lwlock.c where "named tranches" is mentioned.
    >> Maybe we should just say "user-defined tranches" instead?
    > 
    > Like the attached.
    
    > @@ -460,7 +460,7 @@ LWLockShmemInit(void)
    >  }
    >  
    >  /*
    > - * Initialize LWLocks that are fixed and those belonging to named tranches.
    > + * Initialize LWLocks that are fixed and those belonging to user-defined tranches.
    >   */
    >  static void
    >  InitializeLWLocks(int numLocks)
    
    Only tranches requested with RequestNamedLWLockTranche() have locks in 
    the main array, so I reworded this some more to:
    
      /*
       * Initialize LWLocks for built-in tranches and those requested with
       * RequestNamedLWLockTranche().
       */
    
    Committed with that little change, thanks!
    
    - Heikki
    
    
    
    
    
  10. Re: Clean up NamedLWLockTranche stuff

    Sami Imseih <samimseih@gmail.com> — 2026-03-27T14:53:36Z

    > Committed with that little change, thanks!
    
    Thanks!
    
    I think there is one more comment cleanup in lwlock.c
    
     /*
    - * This points to the main array of LWLocks in shared memory.  Backends inherit
    - * the pointer by fork from the postmaster (except in the EXEC_BACKEND case,
    - * where we have special measures to pass it down).
    + * This points to the main array of LWLocks in shared memory.
      */
    
    we no longer need to take special measures to pass down MainLWLockArray
    through the BackendParameters.
    
    --
    Sami
    
  11. Re: Clean up NamedLWLockTranche stuff

    Andres Freund <andres@anarazel.de> — 2026-03-27T21:22:33Z

    Hi,
    
    On 2026-03-27 11:45:56 +0200, Heikki Linnakangas wrote:
    > Committed with that little change, thanks!
    
    This seems to have broken buildfarm animal batta:
    
    https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=batta&dt=2026-03-27%2002%3A05%3A01
    
    # Running: pg_rewind --debug --source-pgdata /home/admin/batta/buildroot/HEAD/pgsql.build/src/bin/pg_rewind/tmp_check/t_001_basic_standby_local_data/pgdata --target-pgdata /home/admin/batta/buildroot/HEAD/pgsql.build/src/bin/pg_rewind/tmp_check/t_001_basic_primary_local_data/pgdata --no-sync --config-file /home/admin/batta/buildroot/HEAD/pgsql.build/src/bin/pg_rewind/tmp_check/tmp_test_QbsG/primary-postgresql.conf.tmp
    pg_rewind: executing "/home/admin/batta/buildroot/HEAD/pgsql.build/tmp_install/home/admin/batta/buildroot/HEAD/inst/bin/postgres" for target server to complete crash recovery
    TRAP: failed Assert("MemoryContextIsValid(context)"), File: "mcxt.c", Line: 1270, PID: 230491
    /home/admin/batta/buildroot/HEAD/pgsql.build/tmp_install/home/admin/batta/buildroot/HEAD/inst/bin/postgres(ExceptionalCondition+0x54)[0xaaaae186c204]
    /home/admin/batta/buildroot/HEAD/pgsql.build/tmp_install/home/admin/batta/buildroot/HEAD/inst/bin/postgres(MemoryContextAllocExtended+0x0)[0xaaaae18a2a24]
    /home/admin/batta/buildroot/HEAD/pgsql.build/tmp_install/home/admin/batta/buildroot/HEAD/inst/bin/postgres(RequestNamedLWLockTranche+0x6c)[0xaaaae16e7310]
    /home/admin/batta/buildroot/HEAD/pgsql.build/tmp_install/home/admin/batta/buildroot/HEAD/inst/bin/postgres(process_shmem_requests+0x28)[0xaaaae1881628]
    /home/admin/batta/buildroot/HEAD/pgsql.build/tmp_install/home/admin/batta/buildroot/HEAD/inst/bin/postgres(PostgresSingleUserMain+0xc4)[0xaaaae1701a34]
    /home/admin/batta/buildroot/HEAD/pgsql.build/tmp_install/home/admin/batta/buildroot/HEAD/inst/bin/postgres(main+0x6ac)[0xaaaae12a2adc]
    /lib/aarch64-linux-gnu/libc.so.6(__libc_start_main+0xe8)[0xffff99713dd8]
    /home/admin/batta/buildroot/HEAD/pgsql.build/tmp_install/home/admin/batta/buildroot/HEAD/inst/bin/postgres(+0xf2b98)[0xaaaae12a2b98]
    Aborted
    pg_rewind: error: postgres single-user mode in target cluster failed
    pg_rewind: detail: Command was: /home/admin/batta/buildroot/HEAD/pgsql.build/tmp_install/home/admin/batta/buildroot/HEAD/inst/bin/postgres --single -F -D /home/admin/batta/buildroot/HEAD/pgsql.build/src/bin/pg_rewind/tmp_check/t_001_basic_primary_local_data/pgdata -c config_file=/home/admin/batta/buildroot/HEAD/pgsql.build/src/bin/pg_rewind/tmp_check/tmp_test_QbsG/primary-postgresql.conf.tmp template1 < /dev/null
    
    Presumably the reason that batta failed is its special configuration:
    
    shared_preload_libraries = 'pg_stat_statements'; regress_dump_restore; wal_consistency_checking; compute_query_id = regress; --enable-injection-points
    
    Greetings,
    
    Andres Freund
    
    
    
    
  12. Re: Clean up NamedLWLockTranche stuff

    Nathan Bossart <nathandbossart@gmail.com> — 2026-03-27T21:50:12Z

    On Fri, Mar 27, 2026 at 05:22:33PM -0400, Andres Freund wrote:
    > TRAP: failed Assert("MemoryContextIsValid(context)"), File: "mcxt.c", Line: 1270, PID: 230491
    > [...](ExceptionalCondition+0x54)[0xaaaae186c204]
    > [...](MemoryContextAllocExtended+0x0)[0xaaaae18a2a24]
    > [...](RequestNamedLWLockTranche+0x6c)[0xaaaae16e7310]
    > [...](process_shmem_requests+0x28)[0xaaaae1881628]
    > [...](PostgresSingleUserMain+0xc4)[0xaaaae1701a34]
    > [...](main+0x6ac)[0xaaaae12a2adc]
    > /lib/aarch64-linux-gnu/libc.so.6(__libc_start_main+0xe8)[0xffff99713dd8]
    > [...](+0xf2b98)[0xaaaae12a2b98]
    > Aborted
    > pg_rewind: error: postgres single-user mode in target cluster failed
    
    Hm.  AFAICT PostmasterContext isn't created in single-user mode, and the
    commit in question has RequestNamedLWLockTranche() allocate requests there.
    I guess the idea is to allow backends to free that memory after forking
    from postmaster, but we don't do that for the NamedLWLockTrancheRequests
    list.  Maybe we should surround the last part of that function with
    MemoryContextSwitchTo(...) to either TopMemoryContext or PostmasterContext
    depending on whether we're in single-user mode.
    
    -- 
    nathan
    
    
    
    
  13. Re: Clean up NamedLWLockTranche stuff

    Nathan Bossart <nathandbossart@gmail.com> — 2026-03-27T22:05:06Z

    On Fri, Mar 27, 2026 at 04:50:12PM -0500, Nathan Bossart wrote:
    > On Fri, Mar 27, 2026 at 05:22:33PM -0400, Andres Freund wrote:
    >> TRAP: failed Assert("MemoryContextIsValid(context)"), File: "mcxt.c", Line: 1270, PID: 230491
    >> [...](ExceptionalCondition+0x54)[0xaaaae186c204]
    >> [...](MemoryContextAllocExtended+0x0)[0xaaaae18a2a24]
    >> [...](RequestNamedLWLockTranche+0x6c)[0xaaaae16e7310]
    >> [...](process_shmem_requests+0x28)[0xaaaae1881628]
    >> [...](PostgresSingleUserMain+0xc4)[0xaaaae1701a34]
    >> [...](main+0x6ac)[0xaaaae12a2adc]
    >> /lib/aarch64-linux-gnu/libc.so.6(__libc_start_main+0xe8)[0xffff99713dd8]
    >> [...](+0xf2b98)[0xaaaae12a2b98]
    >> Aborted
    >> pg_rewind: error: postgres single-user mode in target cluster failed
    > 
    > Hm.  AFAICT PostmasterContext isn't created in single-user mode, and the
    > commit in question has RequestNamedLWLockTranche() allocate requests there.
    > I guess the idea is to allow backends to free that memory after forking
    > from postmaster, but we don't do that for the NamedLWLockTrancheRequests
    > list.  Maybe we should surround the last part of that function with
    > MemoryContextSwitchTo(...) to either TopMemoryContext or PostmasterContext
    > depending on whether we're in single-user mode.
    
    Concretely, like the attached.
    
    -- 
    nathan
    
  14. Re: Clean up NamedLWLockTranche stuff

    Heikki Linnakangas <hlinnaka@iki.fi> — 2026-03-27T22:07:26Z

    On 28/03/2026 00:05, Nathan Bossart wrote:
    > On Fri, Mar 27, 2026 at 04:50:12PM -0500, Nathan Bossart wrote:
    >> On Fri, Mar 27, 2026 at 05:22:33PM -0400, Andres Freund wrote:
    >>> TRAP: failed Assert("MemoryContextIsValid(context)"), File: "mcxt.c", Line: 1270, PID: 230491
    >>> [...](ExceptionalCondition+0x54)[0xaaaae186c204]
    >>> [...](MemoryContextAllocExtended+0x0)[0xaaaae18a2a24]
    >>> [...](RequestNamedLWLockTranche+0x6c)[0xaaaae16e7310]
    >>> [...](process_shmem_requests+0x28)[0xaaaae1881628]
    >>> [...](PostgresSingleUserMain+0xc4)[0xaaaae1701a34]
    >>> [...](main+0x6ac)[0xaaaae12a2adc]
    >>> /lib/aarch64-linux-gnu/libc.so.6(__libc_start_main+0xe8)[0xffff99713dd8]
    >>> [...](+0xf2b98)[0xaaaae12a2b98]
    >>> Aborted
    >>> pg_rewind: error: postgres single-user mode in target cluster failed
    >>
    >> Hm.  AFAICT PostmasterContext isn't created in single-user mode, and the
    >> commit in question has RequestNamedLWLockTranche() allocate requests there.
    >> I guess the idea is to allow backends to free that memory after forking
    >> from postmaster, but we don't do that for the NamedLWLockTrancheRequests
    >> list.  Maybe we should surround the last part of that function with
    >> MemoryContextSwitchTo(...) to either TopMemoryContext or PostmasterContext
    >> depending on whether we're in single-user mode.
    > 
    > Concretely, like the attached.
    
    LGTM, thanks! Will you commit or want me to pick it up?
    
    - Heikki
    
    
    
    
    
  15. Re: Clean up NamedLWLockTranche stuff

    Nathan Bossart <nathandbossart@gmail.com> — 2026-03-27T22:10:16Z

    On Sat, Mar 28, 2026 at 12:07:26AM +0200, Heikki Linnakangas wrote:
    > LGTM, thanks! Will you commit or want me to pick it up?
    
    I'm not able to commit it right this second, so feel free to take it.  Else
    it'll probably be a day or two before I can get to it.
    
    -- 
    nathan
    
    
    
    
  16. Re: Clean up NamedLWLockTranche stuff

    Heikki Linnakangas <hlinnaka@iki.fi> — 2026-03-27T23:02:31Z

    On 28/03/2026 00:10, Nathan Bossart wrote:
    > On Sat, Mar 28, 2026 at 12:07:26AM +0200, Heikki Linnakangas wrote:
    >> LGTM, thanks! Will you commit or want me to pick it up?
    > 
    > I'm not able to commit it right this second, so feel free to take it.  Else
    > it'll probably be a day or two before I can get to it.
    
    Ok, committed, thanks!
    
    - Heikki
    
    
    
    
    
  17. Re: Clean up NamedLWLockTranche stuff

    Sami Imseih <samimseih@gmail.com> — 2026-03-28T17:20:30Z

    Hi Heikki,
    
    Just raising this again to make sure it doesn’t get overlooked [1].
    
    Thanks!
    
    [1] [https://www.postgresql.org/message-id/CAA5RZ0vPWNMvTBqyH7nqDRrHd6Y4Et5iNqXFuwpbsPOk3cL4rQ%40mail.gmail.com]
    
    --
    Sami
    
    
    
    
  18. Re: Clean up NamedLWLockTranche stuff

    Heikki Linnakangas <hlinnaka@iki.fi> — 2026-03-30T14:18:03Z

    On 28/03/2026 19:20, Sami Imseih wrote:
    > Hi Heikki,
    > 
    > Just raising this again to make sure it doesn’t get overlooked [1].
    
    Fixed, thanks!
    
    - Heikki