From: Noah Misch <noah@leadboat.com>
To: pgsql-committers@lists.postgresql.org
Subject: pgsql: Prevent concurrent SimpleLruTruncate() for any given SLRU.
Date: Sat, 15 Aug 2020 17:20:14 +0000
Message-ID: <E1k6zqo-0008VA-Vj@gemulon.postgresql.org> (raw)
Prevent concurrent SimpleLruTruncate() for any given SLRU.
The SimpleLruTruncate() header comment states the new coding rule. To
achieve this, add locktype "frozenid" and two LWLocks. This closes a
rare opportunity for data loss, which manifested as "apparent
wraparound" or "could not access status of transaction" errors. Data
loss is more likely in pg_multixact, due to released branches' thin
margin between multiStopLimit and multiWrapLimit. If a user's physical
replication primary logged ": apparent wraparound" messages, the user
should rebuild standbys of that primary regardless of symptoms. At less
risk is a cluster having emitted "not accepting commands" errors or
"must be vacuumed" warnings at some point. One can test a cluster for
this data loss by running VACUUM FREEZE in every database. Back-patch
to 9.5 (all supported versions).
Discussion: https://postgr.es/m/20190218073103.GA1434723@rfd.leadboat.com
Branch
------
REL_11_STABLE
Details
-------
https://git.postgresql.org/pg/commitdiff/d4031d78460cbbb4ed2fb7be635f84bea0e9a0c1
Modified Files
--------------
doc/src/sgml/catalogs.sgml | 4 +++-
doc/src/sgml/monitoring.sgml | 20 +++++++++++++++--
src/backend/access/transam/slru.c | 8 +++++++
src/backend/access/transam/subtrans.c | 4 ++--
src/backend/commands/async.c | 37 +++++++++++++++++++++++---------
src/backend/commands/vacuum.c | 13 +++++++++++
src/backend/storage/lmgr/lmgr.c | 20 +++++++++++++++++
src/backend/storage/lmgr/lwlocknames.txt | 2 ++
src/backend/utils/adt/lockfuncs.c | 12 +++++++++++
src/include/storage/lmgr.h | 3 +++
src/include/storage/lock.h | 10 +++++++++
11 files changed, 118 insertions(+), 15 deletions(-)
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To: pgsql-committers@postgresql.org
Cc: noah@leadboat.com, pgsql-committers@lists.postgresql.org
Subject: Re: pgsql: Prevent concurrent SimpleLruTruncate() for any given SLRU.
In-Reply-To: <E1k6zqo-0008VA-Vj@gemulon.postgresql.org>
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