Message-ID: <a0edd713-9786-445a-8fd6-0fb30d7038f1@iki.fi>
Date: Thu, 9 Jul 2026 15:17:53 +0300
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: pgsql: Refactor how some aux processes advertise their ProcNumber
To: Fujii Masao <masao.fujii@gmail.com>, Thom Brown <thom@linux.com>
Cc: pgsql-committers@lists.postgresql.org
References: <E1whWIW-000ArK-1q@gemulon.postgresql.org>
 <CAA-aLv6UHXubNxmAjNH8PnyKKkaXePO1ggB15=iidNW08T4hSg@mail.gmail.com>
 <CAHGQGwH8n4BMjBJcL1ob6YTJYn1kTmVwO6mEYoEGyrGyNXaaXw@mail.gmail.com>
Content-Language: en-US
From: Heikki Linnakangas <hlinnaka@iki.fi>
In-Reply-To: 
 <CAHGQGwH8n4BMjBJcL1ob6YTJYn1kTmVwO6mEYoEGyrGyNXaaXw@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Archived-At: 
 <https://www.postgresql.org/message-id/a0edd713-9786-445a-8fd6-0fb30d7038f1%40iki.fi>
Precedence: bulk

On 09/07/2026 03:57, Fujii Masao wrote:
> On Thu, Jul 9, 2026 at 6:57 AM Thom Brown <thom@linux.com> 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