Horton

Re: Improve LWLock tranche name visibility across backends

Bertrand Drouvot <bertranddrouvot.pg@gmail.com>

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From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
To: Sami Imseih <samimseih@gmail.com>
Cc: Nathan Bossart <nathandbossart@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, Andres Freund <andres@anarazel.de>, Rahila Syed <rahilasyed90@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2025-08-29T07:05:14Z
Lists: pgsql-hackers 
Hi,

On Thu, Aug 28, 2025 at 05:53:23PM -0500, Sami Imseih wrote:
> Just a few things that were discussed earlier, that I incorporated now.
> 
> 1/ We should be checking that tranche_name is NOT NULL when
> LWLockNewTrancheId or RequestNamedLWLockTranche is called.

Right, if not strlen() does segfault.

In addition to checking for NULL, should we also check for empty string? Currently,
the patch does accept strlen(tranche_name) == 0.

> Also check for the length of the tranche name inside
> RequestNamedLWLockTranche, instead of relying on an Assert to check
> the length. I think that is much safer.

Same remark as above but in RequestNamedLWLockTranche().

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com

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().