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: Rahila Syed <rahilasyed90@gmail.com>
Cc: Sami Imseih <samimseih@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: 2025-09-04T15:44:00Z
Lists: pgsql-hackers

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On Wed, Sep 03, 2025 at 02:01:14PM -0500, Nathan Bossart wrote:
> Committed.

I'm having some regrets about the changes to RequestNamedLWLockTranche().
Specifically, when it is first called, it immediately allocates an array
big enough to hold 256 requests (~17 KB), whereas it used to only allocate
space for 16 requests (~1 KB) and resize as needed.  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.

-- 
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().