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help / color / mirror / Atom feedFrom: Fujii Masao <fujii@postgresql.org>
To: pgsql-committers@lists.postgresql.org
Subject: pgsql: Prevent stale pg_locks.waitstart values
Date: Mon, 28 Sep 2026 05:24:41 +0000
Message-ID: <E1xB3qz-00000001YkL-1TfY@gemulon.postgresql.org> (raw)
Prevent stale pg_locks.waitstart values
Previously, pg_locks.waitstart could report the start time of a previous
lock wait for a new wait. For a regular backend, this could happen briefly
before the new start time was stored. On a standby, the startup process could
show the old time throughout the next wait, making it appear to have started
earlier than it did.
This happened because PGPROC->waitStart could remain set after a previous
wait in two cases. First, RemoveFromWaitQueue() did not clear it when a wait
was canceled due to a lock timeout, cancellation, or deadlock. Second, even
after a successful lock grant, ProcWakeup() could clear it before the waiter
stored its new start time.
Fix this by clearing waitStart in RemoveFromWaitQueue() when a failed wait
is removed, at the end of ProcSleep() to handle writes made after
ProcWakeup() cleared it, and in LockErrorCleanup() when an error bypasses
the ProcSleep() reset. This prevents pg_locks.waitstart from showing the
previous wait's time for a new wait.
Backpatch to all supported versions.
Author: Shihao Zhong <zhong950419@gmail.com>
Reported-by: Alex Shapalov <shapalov@gmail.com>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Fujii Masao <masao.fujii@gmail.com>
Reviewed-by: Andrew Krylosov <krylosov.andrew@gmail.com>
Discussion: https://postgr.es/m/CAPrb+Q+XN=sNusXiUeWmMo2H7Qgq3Y4uPekSSLkHcnCyf7GhXg@mail.gmail.com
Discussion: https://postgr.es/m/CAGRkXqQLxZBr-ouVrtaX2utMggi4+TiVMbgH04b_0JLgKryxbA@mail.gmail.com
Backpatch-through: 14
Branch
------
REL_14_STABLE
Details
-------
https://git.postgresql.org/pg/commitdiff/edfa6c8fcbfea8721180276855c893ee8fc56598
Modified Files
--------------
src/backend/storage/lmgr/lock.c | 1 +
src/backend/storage/lmgr/proc.c | 9 +++++++++
2 files changed, 10 insertions(+)
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Subject: Re: pgsql: Prevent stale pg_locks.waitstart values
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