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From: Heikki Linnakangas <[email protected]>
To: Fujii Masao <[email protected]>
To: Thom Brown <[email protected]>
Cc: [email protected]
Subject: Re: pgsql: Refactor how some aux processes advertise their ProcNumber
Date: Thu, 9 Jul 2026 15:17:53 +0300
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAHGQGwH8n4BMjBJcL1ob6YTJYn1kTmVwO6mEYoEGyrGyNXaaXw@mail.gmail.com>
References: <[email protected]>
	<CAA-aLv6UHXubNxmAjNH8PnyKKkaXePO1ggB15=iidNW08T4hSg@mail.gmail.com>
	<CAHGQGwH8n4BMjBJcL1ob6YTJYn1kTmVwO6mEYoEGyrGyNXaaXw@mail.gmail.com>

On 09/07/2026 03:57, Fujii Masao wrote:
> On Thu, Jul 9, 2026 at 6:57 AM Thom Brown <[email protected]> wrote:
>> @@ -724,6 +725,14 @@ InitAuxiliaryProcess(void)
>>       */
>>      PGSemaphoreReset(MyProc->sem);
>>
>> +   /* Some aux processes are also advertised in ProcGlobal */
>> +   if (MyBackendType == B_AUTOVAC_LAUNCHER)
>> +       pg_atomic_write_u32(&ProcGlobal->avLauncherProc, MyProcNumber);
>>
>> I'm looking for the places this gets called from. I can only see
>> auxprocess.c which the launcher doesn't go through. The same question
>> for similar code in AuxiliaryProcKill().
> 
> You're right. The autovacuum launcher does not go through
> AuxiliaryProcessMainCommon(), so it never calls
> InitAuxiliaryProcess(). Instead, it initializes its PGPROC with
> InitProcess().
> 
> As a result, the avLauncherProc assignment added to
> InitAuxiliaryProcess() is never executed for the launcher, and the
> corresponding cleanup in AuxiliaryProcKill() is never reached either.

Huh, you're right. That raises some questions:

Why is the autovacuum launcher not an aux process? I guess it's because 
it needs to acquire a heavy-weight lock in order to read the list of 
databases.

How come none of the tests failed? I guess the path to wake up the 
launcher isn't critical for correctness, it just makes autovacuum slower 
to react.

> It seems we should move the avLauncherProc set/clear operations to
> InitProcess()/ProcKill() path, as in the attached patch.
Thanks! Committed that, and also Nathan's volatile removal.

- Heikki

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