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From: Fujii Masao <masao.fujii@gmail.com>
To: JoongHyuk Shin <sjh910805@gmail.com>
Cc: pgsql-hackers@lists.postgresql.org <pgsql-hackers@lists.postgresql.org>
Subject: Re: [PATCH] Prevent repeated deadlock-check signals in standby buffer pin waits
Date: Tue, 21 Apr 2026 14:42:38 +0900
Message-ID: <CAHGQGwFqKOmLNiPhBYB0Bh1Akot=SbTpzMSHA-au4aqVa8PKog@mail.gmail.com> (raw)
In-Reply-To: <CACSdjfO3ox8i8N3KxGf3HThzX1vnRRkY2kq1m5qsvGxjcuM1jg@mail.gmail.com>
References: <CACSdjfO3ox8i8N3KxGf3HThzX1vnRRkY2kq1m5qsvGxjcuM1jg@mail.gmail.com>

On Sun, Apr 19, 2026 at 2:47 PM JoongHyuk Shin <sjh910805@gmail.com> wrote:
>
> In ResolveRecoveryConflictWithBufferPin(), when deadlock_timeout fires,
> the function sends RECOVERY_CONFLICT_BUFFERPIN_DEADLOCK and returns.
> The caller (LockBufferForCleanup) loops back, sets up another deadlock_timeout,
> and the signal gets sent again every interval.
>
> The lock-conflict path had the same problem and was fixed in 8900b5a9d59a
> by adding a second ProcWaitForSignal() after the deadlock-check signal.
> The buffer-pin path was left with an XXX comment asking "should we fix this?".
>
> The attached patch applies the same fix: after sending the deadlock-check
> signal, reset got_standby_deadlock_timeout and call ProcWaitForSignal()
> so the startup process waits for UnpinBuffer() rather than looping
> and re-signaling.
>
> Patch attached.

Thanks for the patch! LGTM.

Since this change improves recovery-conflict behavior rather than fixing a bug,
it doesn't seem to need backpatching and we may need to wait until v20
development opens (probably July) before committing it.

While reading the patch and ResolveRecoveryConflictWithBufferPin(), I also
noticed that got_standby_delay_timeout is not initialized to false before
enabling the timeout. This is unrelated to the patch, and I think it is
harmless in the current code, but would it be better to initialize it there,
as we already do for got_standby_deadlock_timeout?

                    if (ltime != 0)
                    {
    +                       got_standby_delay_timeout = false;
                            timeouts[cnt].id = STANDBY_TIMEOUT;
                            timeouts[cnt].type = TMPARAM_AT;
                            timeouts[cnt].fin_time = ltime;

Regards,

-- 
Fujii Masao

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  Subject: Re: [PATCH] Prevent repeated deadlock-check signals in standby buffer pin waits
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