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Fix data loss at inplace update after heap_update().

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As previously-added tests demonstrated, heap_inplace_update() could
instead update an unrelated tuple of the same catalog.  It could lose
the update.  Losing relhasindex=t was a source of index corruption.
Inplace-updating commands like VACUUM will now wait for heap_update()
commands like GRANT TABLE and GRANT DATABASE.  That isn't ideal, but a
long-running GRANT already hurts VACUUM progress more just by keeping an
XID running.  The VACUUM will behave like a DELETE or UPDATE waiting for
the uncommitted change.

For implementation details, start at the systable_inplace_update_begin()
header comment and README.tuplock.  Back-patch to v12 (all supported
versions).  In back branches, retain a deprecated heap_inplace_update(),
for extensions.

Reported by Smolkin Grigory.  Reviewed by Nitin Motiani, (in earlier
versions) Heikki Linnakangas, and (in earlier versions) Alexander
Lakhin.

Discussion: https://postgr.es/m/CAMp+ueZQz3yDk7qg42hk6-9gxniYbp-=bG2mgqecErqR5gGGOA@mail.gmail.com
This commit is contained in:
Noah Misch
2024-09-24 15:25:18 -07:00
parent dbf3f974ee
commit a07e03fd8f
16 changed files with 801 additions and 155 deletions
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34
src/backend/commands/dbcommands.c
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@ -1651,7 +1651,7 @@ dropdb(const char *dbname, bool missing_ok, bool force)
Relation pgdbrel;
HeapTuple tup;
ScanKeyData scankey;
SysScanDesc scan;
void *inplace_state;
Form_pg_database datform;
int notherbackends;
int npreparedxacts;
@ -1789,24 +1789,6 @@ dropdb(const char *dbname, bool missing_ok, bool force)
*/
pgstat_drop_database(db_id);
/*
* 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(&scankey,
Anum_pg_database_datname,
BTEqualStrategyNumber, F_NAMEEQ,
CStringGetDatum(dbname));
scan = systable_beginscan(pgdbrel, DatabaseNameIndexId, true,
NULL, 1, &scankey);
tup = systable_getnext(scan);
if (!HeapTupleIsValid(tup))
elog(ERROR, "cache lookup failed for database %u", db_id);
datform = (Form_pg_database) GETSTRUCT(tup);
/*
* Except for the deletion of the catalog row, subsequent actions are not
* transactional (consider DropDatabaseBuffers() discarding modified
@ -1818,8 +1800,17 @@ dropdb(const char *dbname, bool missing_ok, bool force)
* modification is durable before performing irreversible filesystem
* operations.
*/
ScanKeyInit(&scankey,
Anum_pg_database_datname,
BTEqualStrategyNumber, F_NAMEEQ,
CStringGetDatum(dbname));
systable_inplace_update_begin(pgdbrel, DatabaseNameIndexId, true,
NULL, 1, &scankey, &tup, &inplace_state);
if (!HeapTupleIsValid(tup))
elog(ERROR, "cache lookup failed for database %u", db_id);
datform = (Form_pg_database) GETSTRUCT(tup);
datform->datconnlimit = DATCONNLIMIT_INVALID_DB;
heap_inplace_update(pgdbrel, tup);
systable_inplace_update_finish(inplace_state, tup);
XLogFlush(XactLastRecEnd);
/*
@ -1827,8 +1818,7 @@ dropdb(const char *dbname, bool missing_ok, bool force)
* the row will be gone, but if we fail, dropdb() can be invoked again.
*/
CatalogTupleDelete(pgdbrel, &tup->t_self);
systable_endscan(scan);
heap_freetuple(tup);
/*
* Drop db-specific replication slots.