From: Nathan Bossart <nathandbossart@gmail.com>
To: Sami Imseih <samimseih@gmail.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: GetNamedLWLockTranche crashes on Windows in normal backend
Date: Mon, 25 Aug 2025 13:31:26 -0500
Message-ID: <aKyr_rVOtlolDcy-@nathan> (raw)
In-Reply-To: <CAA5RZ0u4BDp4ENjOyZ7NADz+jdQY-=PZFQNsf0jBt1Va4QzoAA@mail.gmail.com>
References: <CAA5RZ0v1_15QPg5Sqd2Qz5rh_qcsyCeHHmRDY89xVHcy2yt5BQ@mail.gmail.com>
<aKyTa-iOdAfKynI1@nathan>
<CAA5RZ0u4BDp4ENjOyZ7NADz+jdQY-=PZFQNsf0jBt1Va4QzoAA@mail.gmail.com>
On Mon, Aug 25, 2025 at 12:58:08PM -0500, Sami Imseih wrote:
>> If this fails, why doesn't the call in pgss_shmem_startup() also fail? Was
>> pg_stat_statements not loaded via shared_preload_libraries?
>
> because the array is valid in postmaster, but it's not for a normal backend,
> since it's not getting copied.
>
> Yes, pg_stat_statements was loaded via shared_preload_libraries. Nothing
> was done out of the ordinary.
>
>> And is the
>> failure a segfault or a "requested tranche is not registered" error?
>
> It's a segfault.
Oh, I see what's happening. We are never calling GetNamedLWLockTranche()
in backends because ShmemInitStruct() always sets *found.
I'd argue that calling GetNamedLWLockTranche() outside of an "if (!found)"
block in a shmem_startup_hook doesn't follow convention, but the docs have
this note:
shmem_startup_hook provides a convenient place for the initialization
code, but it is not strictly required that all such code be placed in
this hook.
Like the inaccurate sentence immediately following this one [0], it was
added by commit 964152c. IMHO we should adjust the documentation to match
reality.
[0] https://postgr.es/m/aJ9QIF3g2QQko9wq%40nathan
--
nathan
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To: pgsql-hackers@postgresql.org
Cc: nathandbossart@gmail.com, samimseih@gmail.com
Subject: Re: GetNamedLWLockTranche crashes on Windows in normal backend
In-Reply-To: <aKyr_rVOtlolDcy-@nathan>
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