From: Nathan Bossart <nathandbossart@gmail.com>
To: Sami Imseih <samimseih@gmail.com>
Cc: Alexander Lakhin <exclusion@gmail.com>
Cc: Rahila Syed <rahilasyed90@gmail.com>
Cc: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Andres Freund <andres@anarazel.de>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Improve LWLock tranche name visibility across backends
Date: Mon, 10 Nov 2025 10:49:58 -0600
Message-ID: <aRIXtvkYn1mmyNG5@nathan> (raw)
In-Reply-To: <aRISKd2MEeIqRcOh@nathan>
References: <aLcPbyWLawp5_rdt@nathan>
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<aRISKd2MEeIqRcOh@nathan>
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
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To: pgsql-hackers@postgresql.org
Cc: nathandbossart@gmail.com, samimseih@gmail.com, exclusion@gmail.com, rahilasyed90@gmail.com, bertranddrouvot.pg@gmail.com, tgl@sss.pgh.pa.us, andres@anarazel.de
Subject: Re: Improve LWLock tranche name visibility across backends
In-Reply-To: <aRIXtvkYn1mmyNG5@nathan>
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