Re: Slot's restart_lsn may point to removed WAL segment after hard restart unexpectedly

On Mon, Apr 28, 2025 at 6:39 PM Alexander Korotkov <aekorotkov(at)gmail(dot)com> wrote:
>
> On Tue, Apr 29, 2025 at 4:03 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> >
> > On Mon, Apr 28, 2025 at 8:17 AM Alexander Korotkov <aekorotkov(at)gmail(dot)com> 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 <v(dot)davydov(at)postgrespro(dot)ru> 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