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For inplace update durability, make heap_update() callers wait.

Browse Source 
The previous commit fixed some ways of losing an inplace update.  It
remained possible to lose one when a backend working toward a
heap_update() copied a tuple into memory just before inplace update of
that tuple.  In catalogs eligible for inplace update, use LOCKTAG_TUPLE
to govern admission to the steps of copying an old tuple, modifying it,
and issuing heap_update().  This includes MERGE commands.  To avoid
changing most of the pg_class DDL, don't require LOCKTAG_TUPLE when
holding a relation lock sufficient to exclude inplace updaters.
Back-patch to v12 (all supported versions).  In v13 and v12, "UPDATE
pg_class" or "UPDATE pg_database" can still lose an inplace update.  The
v14+ UPDATE fix needs commit 86dc90056d,
and it wasn't worth reimplementing that fix without such infrastructure.

Reviewed by Nitin Motiani and (in earlier versions) Heikki Linnakangas.

Discussion: https://postgr.es/m/20231027214946.79.nmisch@google.com
This commit is contained in:
Noah Misch
2024-09-24 15:25:18 -07:00
parent 8590c942c1
commit 5c837f8fa0
19 changed files with 490 additions and 49 deletions
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25
src/backend/commands/dbcommands.c
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@ -1750,6 +1750,7 @@ RenameDatabase(const char *oldname, const char *newname)
{
Oid db_id;
HeapTuple newtup;
ItemPointerData otid;
Relation rel;
int notherbackends;
int npreparedxacts;
@ -1821,11 +1822,13 @@ RenameDatabase(const char *oldname, const char *newname)
errdetail_busy_db(notherbackends, npreparedxacts)));
/* rename */
newtup = SearchSysCacheCopy1(DATABASEOID, ObjectIdGetDatum(db_id));
newtup = SearchSysCacheLockedCopy1(DATABASEOID, ObjectIdGetDatum(db_id));
if (!HeapTupleIsValid(newtup))
elog(ERROR, "cache lookup failed for database %u", db_id);
otid = newtup->t_self;
namestrcpy(&(((Form_pg_database) GETSTRUCT(newtup))->datname), newname);
CatalogTupleUpdate(rel, &newtup->t_self, newtup);
CatalogTupleUpdate(rel, &otid, newtup);
UnlockTuple(rel, &otid, InplaceUpdateTupleLock);
InvokeObjectPostAlterHook(DatabaseRelationId, db_id, 0);
@ -2073,6 +2076,7 @@ movedb(const char *dbname, const char *tblspcname)
ereport(ERROR,
(errcode(ERRCODE_UNDEFINED_DATABASE),
errmsg("database \"%s\" does not exist", dbname)));
LockTuple(pgdbrel, &oldtuple->t_self, InplaceUpdateTupleLock);
MemSet(new_record, 0, sizeof(new_record));
MemSet(new_record_nulls, false, sizeof(new_record_nulls));
@ -2085,6 +2089,7 @@ movedb(const char *dbname, const char *tblspcname)
new_record,
new_record_nulls, new_record_repl);
CatalogTupleUpdate(pgdbrel, &oldtuple->t_self, newtuple);
UnlockTuple(pgdbrel, &oldtuple->t_self, InplaceUpdateTupleLock);
InvokeObjectPostAlterHook(DatabaseRelationId, db_id, 0);
@ -2315,6 +2320,7 @@ AlterDatabase(ParseState *pstate, AlterDatabaseStmt *stmt, bool isTopLevel)
ereport(ERROR,
(errcode(ERRCODE_UNDEFINED_DATABASE),
errmsg("database \"%s\" does not exist", stmt->dbname)));
LockTuple(rel, &tuple->t_self, InplaceUpdateTupleLock);
datform = (Form_pg_database) GETSTRUCT(tuple);
dboid = datform->oid;
@ -2368,6 +2374,7 @@ AlterDatabase(ParseState *pstate, AlterDatabaseStmt *stmt, bool isTopLevel)
newtuple = heap_modify_tuple(tuple, RelationGetDescr(rel), new_record,
new_record_nulls, new_record_repl);
CatalogTupleUpdate(rel, &tuple->t_self, newtuple);
UnlockTuple(rel, &tuple->t_self, InplaceUpdateTupleLock);
InvokeObjectPostAlterHook(DatabaseRelationId, dboid, 0);
@ -2417,6 +2424,7 @@ AlterDatabaseRefreshColl(AlterDatabaseRefreshCollStmt *stmt)
if (!pg_database_ownercheck(db_id, GetUserId()))
aclcheck_error(ACLCHECK_NOT_OWNER, OBJECT_DATABASE,
stmt->dbname);
LockTuple(rel, &tuple->t_self, InplaceUpdateTupleLock);
datum = heap_getattr(tuple, Anum_pg_database_datcollversion, RelationGetDescr(rel), &isnull);
oldversion = isnull ? NULL : TextDatumGetCString(datum);
@ -2434,6 +2442,7 @@ AlterDatabaseRefreshColl(AlterDatabaseRefreshCollStmt *stmt)
bool nulls[Natts_pg_database] = {0};
bool replaces[Natts_pg_database] = {0};
Datum values[Natts_pg_database] = {0};
HeapTuple newtuple;
ereport(NOTICE,
(errmsg("changing version from %s to %s",
@ -2442,14 +2451,15 @@ AlterDatabaseRefreshColl(AlterDatabaseRefreshCollStmt *stmt)
values[Anum_pg_database_datcollversion - 1] = CStringGetTextDatum(newversion);
replaces[Anum_pg_database_datcollversion - 1] = true;
tuple = heap_modify_tuple(tuple, RelationGetDescr(rel),
values, nulls, replaces);
CatalogTupleUpdate(rel, &tuple->t_self, tuple);
heap_freetuple(tuple);
newtuple = heap_modify_tuple(tuple, RelationGetDescr(rel),
values, nulls, replaces);
CatalogTupleUpdate(rel, &tuple->t_self, newtuple);
heap_freetuple(newtuple);
}
else
ereport(NOTICE,
(errmsg("version has not changed")));
UnlockTuple(rel, &tuple->t_self, InplaceUpdateTupleLock);
InvokeObjectPostAlterHook(DatabaseRelationId, db_id, 0);
@ -2561,6 +2571,8 @@ AlterDatabaseOwner(const char *dbname, Oid newOwnerId)
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
errmsg("permission denied to change owner of database")));
LockTuple(rel, &tuple->t_self, InplaceUpdateTupleLock);
memset(repl_null, false, sizeof(repl_null));
memset(repl_repl, false, sizeof(repl_repl));
@ -2585,6 +2597,7 @@ AlterDatabaseOwner(const char *dbname, Oid newOwnerId)
newtuple = heap_modify_tuple(tuple, RelationGetDescr(rel), repl_val, repl_null, repl_repl);
CatalogTupleUpdate(rel, &newtuple->t_self, newtuple);
UnlockTuple(rel, &tuple->t_self, InplaceUpdateTupleLock);
heap_freetuple(newtuple);