Horton

Re: Improve LWLock tranche name visibility across backends

Sami Imseih <samimseih@gmail.com>

View thread View on postgr.es
From: Sami Imseih <samimseih@gmail.com>
To: Nathan Bossart <nathandbossart@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Andres Freund <andres@anarazel.de>, Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, Rahila Syed <rahilasyed90@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2025-08-19T21:16:26Z
Lists: pgsql-hackers 
> On Tue, Aug 19, 2025 at 03:52:33PM -0500, Sami Imseih wrote:
> > If we limit the tranche name to NAMEDATALEN and also limit the
> > number of tranches an extension can register, we can put this
> > all in static shared memory (We would still need to have a backend local
> > cache to allow lookups to avoid going to shared memory).
>
> I bet we could avoid the local cache by keeping a backend-local copy of
> LWLockCounter that gets updated as needed.

maybe. If we agree to impose limits ( both name length and # of tranches ),
that will allow us to do things a bit different.

If there is agreement on setting limits, may I propose
1024 tranches and NAMEDATALEN. Both seem reasonably sufficient.

--
Sami

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().