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: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2025-07-15T17:12:06Z
Lists: pgsql-hackers 
On Tue, Jul 15, 2025 at 12:06:00PM -0500, Sami Imseih wrote:
> On Tue, Jul 15, 2025 at 11:57 AM Nathan Bossart
> <nathandbossart@gmail.com> wrote:
>> I was imagining putting the array in one big DSA allocation instead of
>> carting around a pointer for each tranche name.  (Sorry, I realize I am
>> hand-waving over some of the details.)
> 
> I understood it like this. Here is a sketch:
> 
> ```
> dsa_pointer p;
> 
> dsa = dsa_create(....)
> 
> p = dsa_allocate(dsa, LWLockTranchesInitialSize());
> tranche_names = (char **) dsa_get_address(dsa, p);
> tranche_names[0] = "my tranche";
> tranche_names[1] = "my tranche";
> ```
> 
> We will need to track the size and resize if needed.
> 
> Is this what you mean, from a high level?

Yes, that's roughly what I had in mind.  We might need to employ some
tricks to avoid a limit on tranche name length, but maybe that's not worth
the energy.

-- 
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().