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: Rahila Syed <rahilasyed90@gmail.com>
Cc: Nathan Bossart <nathandbossart@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>, Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Date: 2025-08-06T16:56:54Z
Lists: pgsql-hackers 
Thanks for testing!

> Why is it necessary to allocate a new dsa_pointer for tranche names that are the same size and then
> free the old one?
> Is there a reason we can't just assign new_ptrs[i] = old_ptrs[i]?

Fair point. I will updated in the next rev. We don't need to free the'
existing tranche name pointers, only the list.

> Would it be possible to update LWLockInitialize so that it checks if tranche_id is
> already registered in the dsa, and if not, registers it during the LWLockInitialize() process?

We could. I do think this will need a separate discussion as a follow-up to this
thread.

--
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().