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From: Masahiko Sawada <[email protected]>
To: Alexander Korotkov <[email protected]>
Cc: Vitaly Davydov <[email protected]>
Cc: pgsql-hackers <[email protected]>
Subject: Re: Slot's restart_lsn may point to removed WAL segment after hard restart unexpectedly
Date: Tue, 29 Apr 2025 10:25:00 -0700
Message-ID: <CAD21AoDp4Zabk49G94TdWrthfv+0mhHLA6yw-AJxxRSFWPep+g@mail.gmail.com> (raw)
In-Reply-To: <CAPpHfdtgwhFFpb8v8x2Humdj3F_DjaeBWY_h20g-Owh5tMArCA@mail.gmail.com>
References: <1d12d2-67235980-35-19a406a0@63439497>
	<[email protected]>
	<[email protected]>
	<[email protected]>
	<[email protected]>
	<135e8-675c4600-21-304d7f40@228322535>
	<1538a2-67c5c700-7-77ec5a80@179382871>
	<CAPpHfdvQPndPMbPvrHqUYbi_HnTZxxaZ4cafvF+9Mx56v07W-w@mail.gmail.com>
	<27589a-680a4b80-6d-6e07880@117064404>
	<CAPpHfdujSUM6de2ZD6gP_3vjUonHgiqh7StPZ5AQz-=4-qhuzA@mail.gmail.com>
	<CAD21AoAbP8NJN3UZXA=RMB_LMwWFDwkV6Erzf7WpAa=jqs0_6A@mail.gmail.com>
	<CAPpHfdtgwhFFpb8v8x2Humdj3F_DjaeBWY_h20g-Owh5tMArCA@mail.gmail.com>

On Mon, Apr 28, 2025 at 6:39 PM Alexander Korotkov <[email protected]> wrote:
>
> On Tue, Apr 29, 2025 at 4:03 AM Masahiko Sawada <[email protected]> wrote:
> >
> > On Mon, Apr 28, 2025 at 8:17 AM Alexander Korotkov <[email protected]> wrote:
> > >
> > > > I have a question - is there any interest to backport the solution into
> > > > existing major releases?
> > >
> > > As long as this is the bug, it should be backpatched to all supported
> > > affected releases.
> >
> > Yes, but I think we cannot back-patch the proposed fix to back
> > branches as it changes the ReplicationSlot struct defined in slot.h,
> > which breaks ABI compatibility.
>
> Yes, and I think Vitaly already proposed to address this issue.  This
> aspect also needs to be carefully reviewed for sure.
>
> On Thu, Apr 24, 2025 at 5:32 PM Vitaly Davydov <[email protected]> wrote:
> > I can prepare a patch where restart_lsn_flushed stored
> > outside of ReplicationSlot structure and doesn't affect the existing API.

Oh, I totally missed this part. Sorry for making noise. I'll review
the patch once submitted.

Regarding the proposed patch, I think we can somewhat follow
last_saved_confirmed_flush field of ReplicationSlot. For example, we
can set restart_lsn_flushed when restoring the slot from the disk,
etc.

Regards,

-- 
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com






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