diff options
| author | Noah Misch <noah@leadboat.com> | 2020-08-15 10:15:53 -0700 |
|---|---|---|
| committer | Noah Misch <noah@leadboat.com> | 2020-08-15 10:15:53 -0700 |
| commit | 566372b3d6435639e4cc4476d79b8505a0297c87 (patch) | |
| tree | cb23c4c35d85e463569d0759b275f484c240cc47 /src/backend/storage/lmgr/lmgr.c | |
| parent | d4d443b3bbbb3eb9cdc511564ef3c57fde7dd3ac (diff) | |
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
Diffstat (limited to 'src/backend/storage/lmgr/lmgr.c')
| -rw-r--r-- | src/backend/storage/lmgr/lmgr.c | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c index 20103200952..7409de94059 100644 --- a/src/backend/storage/lmgr/lmgr.c +++ b/src/backend/storage/lmgr/lmgr.c @@ -461,6 +461,21 @@ UnlockRelationForExtension(Relation relation, LOCKMODE lockmode) } /* + * LockDatabaseFrozenIds + * + * This allows one backend per database to execute vac_update_datfrozenxid(). + */ +void +LockDatabaseFrozenIds(LOCKMODE lockmode) +{ + LOCKTAG tag; + + SET_LOCKTAG_DATABASE_FROZEN_IDS(tag, MyDatabaseId); + + (void) LockAcquire(&tag, lockmode, false, false); +} + +/* * LockPage * * Obtain a page-level lock. This is currently used by some index access @@ -1098,6 +1113,11 @@ DescribeLockTag(StringInfo buf, const LOCKTAG *tag) tag->locktag_field2, tag->locktag_field1); break; + case LOCKTAG_DATABASE_FROZEN_IDS: + appendStringInfo(buf, + _("pg_database.datfrozenxid of database %u"), + tag->locktag_field1); + break; case LOCKTAG_PAGE: appendStringInfo(buf, _("page %u of relation %u of database %u"), |