Horton

Re: Improve LWLock tranche name visibility across backends

Nathan Bossart <nathandbossart@gmail.com>

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From: Nathan Bossart <nathandbossart@gmail.com>
To: Sami Imseih <samimseih@gmail.com>
Cc: Rahila Syed <rahilasyed90@gmail.com>, Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, Andres Freund <andres@anarazel.de>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2025-09-04T20:37:51Z
Lists: pgsql-hackers 
On Thu, Sep 04, 2025 at 12:30:27PM -0500, Sami Imseih wrote:
> I liked removing the repalloc calls inside this routine and did not think
> it was worth optimizing. I am OK with reverting it back. Although v1
> is incorrect since it's still initializing
> NamedLWLockTrancheRequestArray to MAX_NAMED_TRANCHES

Committed with that fix.

>> Furthermore, the
>> MAX_NAMED_TRANCHES check isn't actually needed because InitializeLWLocks()
>> will do the same check via its calls to LWLockNewTrancheId() for all the
>> named tranche requests.
> 
> I thought about that one and decided to add the error message there, since
> requesting a tranche happens way before LWLockNewTrancheId is called
> during CreateLWLocks, so it was more about erroring out slightly earlier.
> But it may be ok to also just remove it.

We needed it before because the array could only ever hold
MAX_NAMED_TRANCHES requests.

-- 
nathan

Commits

  1. test_dsa: Avoid leaking LWLock tranches.

  2. Teach DSM registry to ERROR if attaching to an uninitialized entry.

  3. Add a test harness for the LWLock tranche code.

  4. Revert recent change to RequestNamedLWLockTranche().

  5. Move dynamically-allocated LWLock tranche names to shared memory.

  6. Prepare DSM registry for upcoming changes to LWLock tranche names.

  7. Add GetNamedDSA() and GetNamedDSHash().