postgres.git / summary / log / commit / refs
commit 5ae01df6f6ef590fd73299050c7112f69c03f3de
Author: Noah Misch <noah@leadboat.com>
Date: Sat Aug 15 17:15:53 2020 +0000
First released in: 14.0, 9.5.24, 9.6.20, 10.15, 11.10, 12.5, 13.0
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
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(-)
diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index b0376d4b542..e611f0d0866 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -8006,7 +8006,8 @@
and general database objects (identified by class OID and object OID,
in the same way as in <structname>pg_description</structname> or
<structname>pg_depend</structname>). Also, the right to extend a
- relation is represented as a separate lockable object.
+ relation is represented as a separate lockable object, as is the right to
+ update <structname>pg_database</structname>.<structfield>datfrozenxid</structfield>.
Also, <quote>advisory</> locks can be taken on numbers that have
user-defined meanings.
</para>
@@ -8032,6 +8033,7 @@
Type of the lockable object:
<literal>relation</>,
<literal>extend</>,
+ <literal>frozenid</literal>,
<literal>page</>,
<literal>tuple</>,
<literal>transactionid</>,
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 31bad1590e5..879c7d8c167 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -789,7 +789,7 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
<tbody>
<row>
- <entry morerows="41"><literal>LWLockNamed</></entry>
+ <entry morerows="43"><literal>LWLockNamed</></entry>
<entry><literal>ShmemIndexLock</></entry>
<entry>Waiting to find or allocate space in shared memory.</entry>
</row>
@@ -974,6 +974,16 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
<entry><literal>OldSnapshotTimeMapLock</></entry>
<entry>Waiting to read or update old snapshot control information.</entry>
</row>
+ <row>
+ <entry><literal>WrapLimitsVacuumLock</literal></entry>
+ <entry>Waiting to update limits on transaction id and multixact
+ consumption.</entry>
+ </row>
+ <row>
+ <entry><literal>NotifyQueueTailLock</literal></entry>
+ <entry>Waiting to update limit on notification message
+ storage.</entry>
+ </row>
<row>
<entry morerows="15"><literal>LWLockTranche</></entry>
<entry><literal>clog</></entry>
@@ -1042,7 +1052,7 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
<entry>Waiting to add or examine predicate lock information.</entry>
</row>
<row>
- <entry morerows="9"><literal>Lock</></entry>
+ <entry morerows="10"><literal>Lock</></entry>
<entry><literal>relation</></entry>
<entry>Waiting to acquire a lock on a relation.</entry>
</row>
@@ -1050,6 +1060,12 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
<entry><literal>extend</></entry>
<entry>Waiting to extend a relation.</entry>
</row>
+ <row>
+ <entry><literal>frozenid</literal></entry>
+ <entry>Waiting to
+ update <structname>pg_database</structname>.<structfield>datfrozenxid</structfield>
+ and <structname>pg_database</structname>.<structfield>datminmxid</structfield>.</entry>
+ </row>
<row>
<entry><literal>page</></entry>
<entry>Waiting to acquire a lock on page of a relation.</entry>
diff --git a/src/backend/access/transam/slru.c b/src/backend/access/transam/slru.c
index e708967e2f3..1f656844917 100644
--- a/src/backend/access/transam/slru.c
+++ b/src/backend/access/transam/slru.c
@@ -1154,6 +1154,14 @@ SimpleLruFlush(SlruCtl ctl, bool allow_redirtied)
/*
* Remove all segments before the one holding the passed page number
+ *
+ * All SLRUs prevent concurrent calls to this function, either with an LWLock
+ * or by calling it only as part of a checkpoint. Mutual exclusion must begin
+ * before computing cutoffPage. Mutual exclusion must end after any limit
+ * update that would permit other backends to write fresh data into the
+ * segment immediately preceding the one containing cutoffPage. Otherwise,
+ * when the SLRU is quite full, SimpleLruTruncate() might delete that segment
+ * after it has accrued freshly-written data.
*/
void
SimpleLruTruncate(SlruCtl ctl, int cutoffPage)
diff --git a/src/backend/access/transam/subtrans.c b/src/backend/access/transam/subtrans.c
index 908fe2d5331..f0409158046 100644
--- a/src/backend/access/transam/subtrans.c
+++ b/src/backend/access/transam/subtrans.c
@@ -335,8 +335,8 @@ ExtendSUBTRANS(TransactionId newestXact)
/*
* Remove all SUBTRANS segments before the one holding the passed transaction ID
*
- * This is normally called during checkpoint, with oldestXact being the
- * oldest TransactionXmin of any running transaction.
+ * oldestXact is the oldest TransactionXmin of any running transaction. This
+ * is called only during checkpoint.
*/
void
TruncateSUBTRANS(TransactionId oldestXact)
diff --git a/src/backend/commands/async.c b/src/backend/commands/async.c
index 3c78eb86f54..125f3b451d0 100644
--- a/src/backend/commands/async.c
+++ b/src/backend/commands/async.c
@@ -224,19 +224,22 @@ typedef struct QueueBackendStatus
/*
* Shared memory state for LISTEN/NOTIFY (excluding its SLRU stuff)
*
- * The AsyncQueueControl structure is protected by the AsyncQueueLock.
+ * The AsyncQueueControl structure is protected by the AsyncQueueLock and
+ * NotifyQueueTailLock.
*
- * When holding the lock in SHARED mode, backends may only inspect their own
- * entries as well as the head and tail pointers. Consequently we can allow a
- * backend to update its own record while holding only SHARED lock (since no
- * other backend will inspect it).
+ * When holding AsyncQueueLock in SHARED mode, backends may only inspect their
+ * own entries as well as the head and tail pointers. Consequently we can
+ * allow a backend to update its own record while holding only SHARED lock
+ * (since no other backend will inspect it).
*
- * When holding the lock in EXCLUSIVE mode, backends can inspect the entries
- * of other backends and also change the head and tail pointers.
+ * When holding AsyncQueueLock in EXCLUSIVE mode, backends can inspect the
+ * entries of other backends and also change the head pointer. When holding
+ * both AsyncQueueLock and NotifyQueueTailLock in EXCLUSIVE mode, backends can
+ * change the tail pointer.
*
* AsyncCtlLock is used as the control lock for the pg_notify SLRU buffers.
- * In order to avoid deadlocks, whenever we need both locks, we always first
- * get AsyncQueueLock and then AsyncCtlLock.
+ * In order to avoid deadlocks, whenever we need multiple locks, we first get
+ * NotifyQueueTailLock, then AsyncQueueLock, and lastly AsyncCtlLock.
*
* Each backend uses the backend[] array entry with index equal to its
* BackendId (which can range from 1 to MaxBackends). We rely on this to make
@@ -2013,6 +2016,10 @@ asyncQueueAdvanceTail(void)
int newtailpage;
int boundary;
+ /* Restrict task to one backend per cluster; see SimpleLruTruncate(). */
+ LWLockAcquire(NotifyQueueTailLock, LW_EXCLUSIVE);
+
+ /* Compute the new tail. */
LWLockAcquire(AsyncQueueLock, LW_EXCLUSIVE);
min = QUEUE_HEAD;
for (i = 1; i <= MaxBackends; i++)
@@ -2021,7 +2028,6 @@ asyncQueueAdvanceTail(void)
min = QUEUE_POS_MIN(min, QUEUE_BACKEND_POS(i));
}
oldtailpage = QUEUE_POS_PAGE(QUEUE_TAIL);
- QUEUE_TAIL = min;
LWLockRelease(AsyncQueueLock);
/*
@@ -2041,6 +2047,17 @@ asyncQueueAdvanceTail(void)
*/
SimpleLruTruncate(AsyncCtl, newtailpage);
}
+
+ /*
+ * Advertise the new tail. This changes asyncQueueIsFull()'s verdict for
+ * the segment immediately prior to the new tail, allowing fresh data into
+ * that segment.
+ */
+ LWLockAcquire(AsyncQueueLock, LW_EXCLUSIVE);
+ QUEUE_TAIL = min;
+ LWLockRelease(AsyncQueueLock);
+
+ LWLockRelease(NotifyQueueTailLock);
}
/*
diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index 52c4c654061..edc7642cc44 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -891,6 +891,14 @@ vac_update_datfrozenxid(void)
bool bogus = false;
bool dirty = false;
+ /*
+ * Restrict this task to one backend per database. This avoids race
+ * conditions that would move datfrozenxid or datminmxid backward. It
+ * avoids calling vac_truncate_clog() with a datfrozenxid preceding a
+ * datfrozenxid passed to an earlier vac_truncate_clog() call.
+ */
+ LockDatabaseFrozenIds(ExclusiveLock);
+
/*
* Initialize the "min" calculation with GetOldestXmin, which is a
* reasonable approximation to the minimum relfrozenxid for not-yet-
@@ -1055,6 +1063,9 @@ vac_truncate_clog(TransactionId frozenXID,
bool bogus = false;
bool frozenAlreadyWrapped = false;
+ /* Restrict task to one backend per cluster; see SimpleLruTruncate(). */
+ LWLockAcquire(WrapLimitsVacuumLock, LW_EXCLUSIVE);
+
/* init oldest datoids to sync with my frozenXID/minMulti values */
oldestxid_datoid = MyDatabaseId;
minmulti_datoid = MyDatabaseId;
@@ -1156,6 +1167,8 @@ vac_truncate_clog(TransactionId frozenXID,
SetTransactionIdLimit(frozenXID, oldestxid_datoid);
SetMultiXactIdLimit(minMulti, minmulti_datoid);
AdvanceOldestCommitTsXid(frozenXID);
+
+ LWLockRelease(WrapLimitsVacuumLock);
}
diff --git a/src/backend/storage/lmgr/lmgr.c b/src/backend/storage/lmgr/lmgr.c
index 0b9f105b531..7b87002d7ce 100644
--- a/src/backend/storage/lmgr/lmgr.c
+++ b/src/backend/storage/lmgr/lmgr.c
@@ -412,6 +412,21 @@ UnlockRelationForExtension(Relation relation, LOCKMODE lockmode)
LockRelease(&tag, lockmode, false);
}
+/*
+ * 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
*
@@ -1015,6 +1030,11 @@ 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"),
diff --git a/src/backend/storage/lmgr/lwlocknames.txt b/src/backend/storage/lmgr/lwlocknames.txt
index f8996cd21a5..d9afe60e29a 100644
--- a/src/backend/storage/lmgr/lwlocknames.txt
+++ b/src/backend/storage/lmgr/lwlocknames.txt
@@ -47,3 +47,5 @@ CommitTsLock 39
ReplicationOriginLock 40
MultiXactTruncationLock 41
OldSnapshotTimeMapLock 42
+WrapLimitsVacuumLock 46
+NotifyQueueTailLock 47
diff --git a/src/backend/utils/adt/lockfuncs.c b/src/backend/utils/adt/lockfuncs.c
index 2e55368061d..3b5627d8879 100644
--- a/src/backend/utils/adt/lockfuncs.c
+++ b/src/backend/utils/adt/lockfuncs.c
@@ -26,6 +26,7 @@
const char *const LockTagTypeNames[] = {
"relation",
"extend",
+ "frozenid",
"page",
"tuple",
"transactionid",
@@ -245,6 +246,17 @@ pg_lock_status(PG_FUNCTION_ARGS)
nulls[8] = true;
nulls[9] = true;
break;
+ case LOCKTAG_DATABASE_FROZEN_IDS:
+ values[1] = ObjectIdGetDatum(instance->locktag.locktag_field1);
+ nulls[2] = true;
+ nulls[3] = true;
+ nulls[4] = true;
+ nulls[5] = true;
+ nulls[6] = true;
+ nulls[7] = true;
+ nulls[8] = true;
+ nulls[9] = true;
+ break;
case LOCKTAG_PAGE:
values[1] = ObjectIdGetDatum(instance->locktag.locktag_field1);
values[2] = ObjectIdGetDatum(instance->locktag.locktag_field2);
diff --git a/src/include/storage/lmgr.h b/src/include/storage/lmgr.h
index 8288e7d5054..0a889e718f5 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 cc9d8f7136a..f425c3b56e0 100644
--- a/src/include/storage/lock.h
+++ b/src/include/storage/lock.h
@@ -142,6 +142,8 @@ 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 */
@@ -207,6 +209,14 @@ 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), \
[parent: 7241edc4fa8c]