Horton

Re: Improve LWLock tranche name visibility across backends

Sami Imseih <samimseih@gmail.com>

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From: Sami Imseih <samimseih@gmail.com>
To: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Cc: Nathan Bossart <nathandbossart@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2025-08-04T15:33:01Z
Lists: pgsql-hackers 
> > I think we could add a local backend copy that stays up to date with the
> > DSA. One idea would be to use an atomic counter to track the number of
> > entries in the DSA and compare it with a local backend counter whenever the
> > tranche name lookup occurs. If the atomic counter is higher (since we
> > don't have deletions),
> > we can update the local copy. Updating the local table should be a
> > rare occurrence, but it would
> > require an additional atomic fetch every time the name lookup occurs, in all the
> > above code paths.
> >
> > Perhaps there's a better approach?
>
> I was thinking to switch to the DSA (and update local copy) when a name is
> not found in the local copy. That way there is no need to maintain a counter and
> the DSA overhead should be rare enough.
>
> Regards,

That should work as well. good idea.

--
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().