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: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Cc: Sami Imseih <samimseih@gmail.com>, Rahila Syed <rahilasyed90@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2025-08-19T17:29:14Z
Lists: pgsql-hackers 
On Tue, Aug 19, 2025 at 08:09:53AM +0000, Bertrand Drouvot wrote:
> On Mon, Aug 18, 2025 at 05:53:44PM -0500, Sami Imseih wrote:
>> > (or some other shmem-based
>> > data structure we have yet to introduce, like a dslist/dsarray).
>> 
>> This will be an interesting API to invest time in, if there could be more
>> use-cases.
> 
> I did a quick check and I did not find current use cases: possible candidates
> could be in ExecParallelHashTableAlloc(), PTIterationArray, PTEntryArray for
> examples but I think they all know the final size upfront so there is no real
> need for dsarray for those).
> 
>> I think it's a separate discussion at this point.
> 
> OTOH, that would be a valid use case to introduce this new API but I'm not sure
> it's worth it given that the dshash looks good enough for our case (even if not
> ideal though).

IMHO it'd be okay to proceed with dshash for now.  It would be pretty easy
to switch to something like a "dslist" in the future.

-- 
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().