Re: Improve LWLock tranche name visibility across backends

On Mon, Nov 10, 2025 at 10:26:17AM -0600, Nathan Bossart wrote:
> On Mon, Nov 03, 2025 at 11:50:48AM -0600, Sami Imseih wrote:
>>>> I am not sure we need to do anything about this.
>>>
>>> Or maybe we just avoid the tranche_id from leaking
>>> in test_dsa_resowners() by making it a static variable
>>> and checking if we have a valid tranche id before calling
>>> LWLockNewTrancheId()? That is the proper pattern.
>>
>> Like the attached.
>
> It's probably a good idea to avoid tranche leaks, but IMHO there's room for
> improvement in the DSM registry, too. IIUC the problem is that the DSM
> segment is still being added to the registry and found by other backends
> despite the initialization callback failing. My first instinct is that we
> should keep track of whether the DSM segments/DSAs/dshash tables in the
> registry have been fully initialized and to just ERROR in other backends
> when attaching if they aren't. That shouldn't really happen in practice,
> but it'd be good to avoid the strange errors, anyway.

BTW if we really wanted to avoid leaking tranches in test_dsa, we'd need to
store the ID in shared memory. Your patch helps in the case where a single
backend is repeatedly calling test_dsa_resowners(), but other backends
would still allocate their own tranche. I don't see a strong need to fix
this on back-branches, given these functions run exactly once as part of a
test, but fixing it on master seems worthwhile so that extension authors
don't copy/paste this broken code.

--
nathan