diff options
| author | Noah Misch | 2020-08-15 17:15:53 +0000 |
|---|---|---|
| committer | Noah Misch | 2020-08-15 17:15:57 +0000 |
| commit | d4031d78460cbbb4ed2fb7be635f84bea0e9a0c1 (patch) | |
| tree | d7ee345e4522f52d62b51f33db15d96ba9a8535a /src/include | |
| parent | 9d472b51e98777102d72f8ccdfb8cef10e087f74 (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/include')
| -rw-r--r-- | src/include/storage/lmgr.h | 3 | ||||
| -rw-r--r-- | src/include/storage/lock.h | 10 |
2 files changed, 13 insertions, 0 deletions
diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h index a217de97166..13667584ea0 100644 --- a/src/include/storage/lmgr.h +++ b/src/include/storage/lmgr.h @@ -57,6 +57,9 @@ extern bool ConditionalLockRelationForExtension(Relation relation, LOCKMODE lockmode); extern int RelationExtensionLockWaiterCount(Relation relation); +/* Lock to recompute pg_database.datfrozenxid in the current database */ +extern void LockDatabaseFrozenIds(LOCKMODE lockmode); + /* Lock a page (currently only used within indexes) */ extern void LockPage(Relation relation, BlockNumber blkno, LOCKMODE lockmode); extern bool ConditionalLockPage(Relation relation, BlockNumber blkno, LOCKMODE lockmode); diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ff4df7fec51..6b56fa58743 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -141,6 +141,8 @@ typedef enum LockTagType /* ID info for a relation is DB OID + REL OID; DB OID = 0 if shared */ LOCKTAG_RELATION_EXTEND, /* the right to extend a relation */ /* same ID info as RELATION */ + LOCKTAG_DATABASE_FROZEN_IDS, /* pg_database.datfrozenxid */ + /* ID info for frozen IDs is DB OID */ LOCKTAG_PAGE, /* one page of a relation */ /* ID info for a page is RELATION info + BlockNumber */ LOCKTAG_TUPLE, /* one physical tuple */ @@ -206,6 +208,14 @@ typedef struct LOCKTAG (locktag).locktag_type = LOCKTAG_RELATION_EXTEND, \ (locktag).locktag_lockmethodid = DEFAULT_LOCKMETHOD) +#define SET_LOCKTAG_DATABASE_FROZEN_IDS(locktag,dboid) \ + ((locktag).locktag_field1 = (dboid), \ + (locktag).locktag_field2 = 0, \ + (locktag).locktag_field3 = 0, \ + (locktag).locktag_field4 = 0, \ + (locktag).locktag_type = LOCKTAG_DATABASE_FROZEN_IDS, \ + (locktag).locktag_lockmethodid = DEFAULT_LOCKMETHOD) + #define SET_LOCKTAG_PAGE(locktag,dboid,reloid,blocknum) \ ((locktag).locktag_field1 = (dboid), \ (locktag).locktag_field2 = (reloid), \ |