Horton

Re: Clean up NamedLWLockTranche stuff

Sami Imseih <samimseih@gmail.com>

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From: Sami Imseih <samimseih@gmail.com>
To: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Nathan Bossart <nathandbossart@gmail.com>, Robert Haas <robertmhaas@gmail.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2026-03-27T03:57:44Z
Lists: pgsql-hackers 
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)

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 Fix outdated comment on MainLWLockArray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.