Re: Introduce XID age based replication slot invalidation

On Sun, Apr 5, 2026 at 7:52 PM Bharath Rupireddy
<bharath(dot)rupireddyforpostgres(at)gmail(dot)com> wrote:
>
> Hi,
>
> On Sun, Apr 5, 2026 at 1:03 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> >
> > Thank you for updating the patch!
> >
> > I've made some changes including moving MaybeInvalidateXidAgedSlot()
> > to vacuum.c since the function seems more inherently tied to vacuum
> > context. Also, updated the commit message and fixed typos.
> >
> > Please review the attached patch.
>
> Thank you Sawada-san!
>
> I took a look at the v10 patch and it LGTM. I tested it - make
> check-world passes, pgindent doesn't complain.
>

While reviewing the patch, I found that with this patch, backend
processes and autovacuum workers can simultaneously attempt to
invalidate the same slot for the same reason. When invalidating a
slot, we send a signal to the process owning the slot and wait for it
to exit and release the slot. If the process takes a long time to exit
for some reason, subsequent autovacuum workers attempting to
invalidate the same slot will also send a SIGTERM and get stuck at
InvalidatePossiblyObsoleteSlot(). In the worst case, this could result
in all autovacuum activity being blocked. I think we need to address
this problem.

Regards,

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