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From: Amit Kapila <amit.kapila16@gmail.com>
Date: Tue, 16 Jun 2026 15:05:39 +0530
Message-ID: 
 <CAA4eK1K7e1Y2iYkmRZ5CCh0pZOTMUShKDj0nP4nY3Wdcypt7oQ@mail.gmail.com>
Subject: Re: Fix race in ReplicationSlotRelease for ephemeral slots
To: "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>
Cc: Xuneng Zhou <xunengzhou@gmail.com>, Fujii Masao <masao.fujii@gmail.com>,
	Srinath Reddy Sadipiralla <srinath2133@gmail.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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On Tue, Jun 16, 2026 at 2:24=E2=80=AFPM Zhijie Hou (Fujitsu)
<houzj.fnst@fujitsu.com> wrote:
>
> On Tuesday, June 16, 2026 1:30 PM Xuneng Zhou <xunengzhou@gmail.com> wrot=
e:
> > On Fri, Jun 12, 2026 at 6:54=E2=80=AFPM Amit Kapila <amit.kapila16@gmai=
l.com>
> > wrote:
> > >
> > > On Fri, Jun 12, 2026 at 8:22=E2=80=AFAM Xuneng Zhou <xunengzhou@gmail=
.com>
> > wrote:
> > > >
> > > > On Thu, Jun 11, 2026 at 9:19=E2=80=AFPM Fujii Masao <masao.fujii@gm=
ail.com>
> > > > In an off-list chat with Zhijie, we kinda thought that holding the
> > > > lock of a wrong db for a brief time doesn't seem to harm a lot. The
> > > > concurrent dropping-db operation leads to this issue seems rare in
> > > > practice. He stated that the deletion of the slot seems unavoidable
> > > > because we have to acquire the database lock after releasing the
> > > > replication slot lock to avoid the deadlock with the startup/drop d=
b
> > > > operation. Therefore, he prefered keeping the design simple and
> > > > avoiding the fatal issue over doing a broader refactoring work.
> > > >
> > >
> > > +1. I also think this change is not worth it.
> >
> > I am also OK with the scope of change made by patch 1.
>
> I have one minor comment for the 0001 patch.
>
> +                       NameData        slot_name =3D {0};
> ...
>                         SpinLockAcquire(&local_slot->mutex);
>                         synced_slot =3D local_slot->in_use && local_slot-=
>data.synced;
> +                       if (synced_slot)
> +                               slot_name =3D local_slot->data.name;
>                         SpinLockRelease(&local_slot->mutex);
>
> We can defer assigning slot_name until after we pass the existing (synced=
_slot)
> check. Since it's a synced slot, no other process can change it at that p=
oint,
> and we can also skip initializing slot_name. (Please refer to the
> attached patch for suggested changes)
>

+ if (dropped)
+ ereport(LOG,
+ errmsg("dropped replication slot \"%s\" of database with OID %u",
+    NameStr(slot_name),
+    slot_database));

Can we avoid the if (dropped) check by placing this LOG message
immediately after dropping the slot under synced slot check?

--=20
With Regards,
Amit Kapila.