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From: Fujii Masao <masao.fujii@gmail.com>
Date: Tue, 16 Jun 2026 21:45:55 +0900
Message-ID: 
 <CAHGQGwGGyEDL3dh7uJ6qPsGvnq4QK_R8+U=12CaprnzwrwaLGA@mail.gmail.com>
Subject: Re: Fix race in ReplicationSlotRelease for ephemeral slots
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Xuneng Zhou <xunengzhou@gmail.com>,
 "Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>,
	Srinath Reddy Sadipiralla <srinath2133@gmail.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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On Fri, Jun 12, 2026 at 7:54=E2=80=AFPM Amit Kapila <amit.kapila16@gmail.co=
m> wrote:
> I feel even if there is an argument to do such a refactoring, it can
> be done separately. We can push forward with 0001 and then do more
> discussion for 0002, if required. I can take care of 0001 unless
> Fujii-San wishes to take care of it?

Yeah, please feel free to work on 0001.

Regarding 0002, since the race is very rare and non-fatal, I'm okay
with accepting the risk rather than adding more refactoring just to
avoid it.

I'm a bit tempted to add a source comment explaining the risk and
why we accept it, though, so other developers can understand
the tradeoff. For example:

diff --git a/src/backend/replication/logical/slotsync.c
b/src/backend/replication/logical/slotsync.c
index 05637344363..ca49f20e7d9 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -560,6 +560,12 @@ drop_local_obsolete_slots(List *remote_slot_list)
                         * the same shared memory as that of
'local_slot'. Thus check if
                         * local_slot is still the synced one before
performing the actual
                         * drop.
+                        *
+                        * Because local_slot still points to a
reusable slot-array entry,
+                        * fields such as name or database OID could
already be stale here.
+                        * That could cause an incorrect cleanup
decision for this cycle or
+                        * briefly lock an unrelated database. We
accept that risk because
+                        * this race is rare and non-fatal.
                         */
                        SpinLockAcquire(&local_slot->mutex);
                        synced_slot =3D local_slot->in_use &&
local_slot->data.synced;

Regards,

--=20
Fujii Masao