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help / color / mirror / Atom feedFrom: Amit Kapila <akapila@postgresql.org>
To: pgsql-committers@lists.postgresql.org
Subject: pgsql: Expand comment on the slot recheck in drop_local_obsolete_slots(
Date: Thu, 02 Jul 2026 04:10:33 +0000
Message-ID: <E1wf8kz-0012Ax-0x@gemulon.postgresql.org> (raw)
Expand comment on the slot recheck in drop_local_obsolete_slots().
The existing comment explained that a user-created slot could reuse the
same shared memory as 'local_slot' during the window between selecting a
slot to drop and locking its database, and that we therefore recheck
before dropping. It did not, however, spell out the fuller consequence:
because local_slot points to a reusable slot-array entry, its fields may
already describe a replacement slot, so the earlier drop decision and the
slot_database used for locking could relate to an unrelated slot/database.
Expand the comment to describe this, and note that the recheck prevents
us from dropping a user-created replacement slot while the residual risk
(such as briefly locking an unrelated database) is confined to the cycle
and is acceptable given the race is rare and non-fatal.
No functional change.
Author: Fujii Masao <masao.fujii@gmail.com>
Author: Xuneng Zhou <xunengzhou@gmail.com>
Author: Amit Kapila <amit.kapila16@gmail.com>
Discussion: https://postgr.es/m/CAHGQGwGGyEDL3dh7uJ6qPsGvnq4QK_R8+U=12CaprnzwrwaLGA@mail.gmail.com
Discussion: https://postgr.es/m/CAHGQGwHqQ1PPVFfYKVxLfRyC-byRdwSN0NeaHj9SLYV97oO5cw@mail.gmail.com
Branch
------
master
Details
-------
https://git.postgresql.org/pg/commitdiff/6b41bd1a459cb457cbb51d021b70004646d78db0
Modified Files
--------------
src/backend/replication/logical/slotsync.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)
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To: pgsql-committers@postgresql.org
Cc: akapila@postgresql.org, pgsql-committers@lists.postgresql.org
Subject: Re: pgsql: Expand comment on the slot recheck in drop_local_obsolete_slots(
In-Reply-To: <E1wf8kz-0012Ax-0x@gemulon.postgresql.org>
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