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authorMichael Paquier2023-01-11 00:56:14 +0000
committerMichael Paquier2023-01-11 00:56:14 +0000
commit72b6098be47e19eff50a052676908e0fde25e7ee (patch)
tree1d18e8ea8618a1870b70a8a0c7bd28ac4e2d3e4f /src
parent2ad4abedfeec23098c8066cf177216238224a60a (diff)
Avoid using tuple from syscache for update of pg_database.datfrozenxid
pg_database.datfrozenxid gets updated using an in-place update at the end of vacuum or autovacuum. Since 96cdeae, as pg_database has a toast relation, it is possible for a pg_database tuple to have toast values if there is a large set of ACLs in place. In such a case, the in-place update would fail because of the flattening of the toast values done for the catcache entry fetched. Instead of using a copy from the catcache, this changes the logic to fetch the copy of the tuple by directly scanning pg_database. Note that before 96cdeae, attempting to insert such a tuple to pg_database would cause a "row is too big" error, so the end-of-vacuum problem was not reachable. This issue has been originally fixed in 947789f on v14~, and there have been reports about this problem on v12 and v13, causing failures at the end of VACUUM. This completes the fix on all the stable branches where pg_database can use a toast table, down to 12. Author: Ashwin Agrawal, Junfeng Yang Discussion: https://postgr.es/m/DM5PR0501MB38800D9E4605BCA72DD35557CCE10@DM5PR0501MB3880.namprd05.prod.outlook.com Discussion: https://postgr.es/m/Y70XNVbUWQsR2Car@paquier.xyz Backpatch-through: 12
Diffstat (limited to 'src')
-rw-r--r--src/backend/access/heap/heapam.c4
-rw-r--r--src/backend/commands/vacuum.c21
2 files changed, 23 insertions, 2 deletions
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index fbe7c222f73..1bd22f9e996 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -5806,6 +5806,10 @@ heap_abort_speculative(Relation relation, ItemPointer tid)
*
* tuple is an in-memory tuple structure containing the data to be written
* over the target tuple. Also, tuple->t_self identifies the target tuple.
+ *
+ * Note that the tuple updated here had better not come directly from the
+ * syscache if the relation has a toast relation as this tuple could
+ * include toast values that have been expanded, causing a failure here.
*/
void
heap_inplace_update(Relation relation, HeapTuple tuple)
diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index 5ef6698790c..8010a7cd470 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -31,6 +31,7 @@
#include "access/tableam.h"
#include "access/transam.h"
#include "access/xact.h"
+#include "catalog/indexing.h"
#include "catalog/namespace.h"
#include "catalog/pg_database.h"
#include "catalog/pg_inherits.h"
@@ -1343,6 +1344,7 @@ vac_update_datfrozenxid(void)
MultiXactId lastSaneMinMulti;
bool bogus = false;
bool dirty = false;
+ ScanKeyData key[1];
/*
* Restrict this task to one backend per database. This avoids race
@@ -1460,10 +1462,25 @@ vac_update_datfrozenxid(void)
/* Now fetch the pg_database tuple we need to update. */
relation = table_open(DatabaseRelationId, RowExclusiveLock);
- /* Fetch a copy of the tuple to scribble on */
- tuple = SearchSysCacheCopy1(DATABASEOID, ObjectIdGetDatum(MyDatabaseId));
+ /*
+ * Get the pg_database tuple to scribble on. Note that this does not
+ * directly rely on the syscache to avoid issues with flattened toast
+ * values for the in-place update.
+ */
+ ScanKeyInit(&key[0],
+ Anum_pg_database_oid,
+ BTEqualStrategyNumber, F_OIDEQ,
+ ObjectIdGetDatum(MyDatabaseId));
+
+ scan = systable_beginscan(relation, DatabaseOidIndexId, true,
+ NULL, 1, key);
+ tuple = systable_getnext(scan);
+ tuple = heap_copytuple(tuple);
+ systable_endscan(scan);
+
if (!HeapTupleIsValid(tuple))
elog(ERROR, "could not find tuple for database %u", MyDatabaseId);
+
dbform = (Form_pg_database) GETSTRUCT(tuple);
/*