diff options
Diffstat (limited to 'src/backend/commands/dbcommands.c')
| -rw-r--r-- | src/backend/commands/dbcommands.c | 66 |
1 files changed, 8 insertions, 58 deletions
diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c index 0e10a752180..a3a150d7008 100644 --- a/src/backend/commands/dbcommands.c +++ b/src/backend/commands/dbcommands.c @@ -133,7 +133,6 @@ createdb(const CreatedbStmt *stmt) int notherbackends; int npreparedxacts; createdb_failure_params fparms; - Snapshot snapshot; /* Extract options from the statement node tree */ foreach(option, stmt->options) @@ -538,29 +537,6 @@ createdb(const CreatedbStmt *stmt) RequestCheckpoint(CHECKPOINT_IMMEDIATE | CHECKPOINT_FORCE | CHECKPOINT_WAIT); /* - * Take an MVCC snapshot to use while scanning through pg_tablespace. For - * safety, register the snapshot (this prevents it from changing if - * something else were to request a snapshot during the loop). - * - * Traversing pg_tablespace with an MVCC snapshot is necessary to provide - * us with a consistent view of the tablespaces that exist. Using - * SnapshotNow here would risk seeing the same tablespace multiple times, - * or worse not seeing a tablespace at all, if its tuple is moved around - * by a concurrent update (eg an ACL change). - * - * Inconsistency of this sort is inherent to all SnapshotNow scans, unless - * some lock is held to prevent concurrent updates of the rows being - * sought. There should be a generic fix for that, but in the meantime - * it's worth fixing this case in particular because we are doing very - * heavyweight operations within the scan, so that the elapsed time for - * the scan is vastly longer than for most other catalog scans. That - * means there's a much wider window for concurrent updates to cause - * trouble here than anywhere else. XXX this code should be changed - * whenever a generic fix is implemented. - */ - snapshot = RegisterSnapshot(GetLatestSnapshot()); - - /* * Once we start copying subdirectories, we need to be able to clean 'em * up if we fail. Use an ENSURE block to make sure this happens. (This * is not a 100% solution, because of the possibility of failure during @@ -577,7 +553,7 @@ createdb(const CreatedbStmt *stmt) * each one to the new database. */ rel = heap_open(TableSpaceRelationId, AccessShareLock); - scan = heap_beginscan(rel, snapshot, 0, NULL); + scan = heap_beginscan_catalog(rel, 0, NULL); while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL) { Oid srctablespace = HeapTupleGetOid(tuple); @@ -682,9 +658,6 @@ createdb(const CreatedbStmt *stmt) PG_END_ENSURE_ERROR_CLEANUP(createdb_failure_callback, PointerGetDatum(&fparms)); - /* Free our snapshot */ - UnregisterSnapshot(snapshot); - return dboid; } @@ -1214,7 +1187,7 @@ movedb(const char *dbname, const char *tblspcname) BTEqualStrategyNumber, F_NAMEEQ, NameGetDatum(dbname)); sysscan = systable_beginscan(pgdbrel, DatabaseNameIndexId, true, - SnapshotNow, 1, &scankey); + NULL, 1, &scankey); oldtuple = systable_getnext(sysscan); if (!HeapTupleIsValid(oldtuple)) /* shouldn't happen... */ ereport(ERROR, @@ -1403,7 +1376,7 @@ AlterDatabase(AlterDatabaseStmt *stmt, bool isTopLevel) BTEqualStrategyNumber, F_NAMEEQ, NameGetDatum(stmt->dbname)); scan = systable_beginscan(rel, DatabaseNameIndexId, true, - SnapshotNow, 1, &scankey); + NULL, 1, &scankey); tuple = systable_getnext(scan); if (!HeapTupleIsValid(tuple)) ereport(ERROR, @@ -1498,7 +1471,7 @@ AlterDatabaseOwner(const char *dbname, Oid newOwnerId) BTEqualStrategyNumber, F_NAMEEQ, NameGetDatum(dbname)); scan = systable_beginscan(rel, DatabaseNameIndexId, true, - SnapshotNow, 1, &scankey); + NULL, 1, &scankey); tuple = systable_getnext(scan); if (!HeapTupleIsValid(tuple)) ereport(ERROR, @@ -1637,7 +1610,7 @@ get_db_info(const char *name, LOCKMODE lockmode, NameGetDatum(name)); scan = systable_beginscan(relation, DatabaseNameIndexId, true, - SnapshotNow, 1, &scanKey); + NULL, 1, &scanKey); tuple = systable_getnext(scan); @@ -1751,20 +1724,9 @@ remove_dbtablespaces(Oid db_id) Relation rel; HeapScanDesc scan; HeapTuple tuple; - Snapshot snapshot; - - /* - * As in createdb(), we'd better use an MVCC snapshot here, since this - * scan can run for a long time. Duplicate visits to tablespaces would be - * harmless, but missing a tablespace could result in permanently leaked - * files. - * - * XXX change this when a generic fix for SnapshotNow races is implemented - */ - snapshot = RegisterSnapshot(GetLatestSnapshot()); rel = heap_open(TableSpaceRelationId, AccessShareLock); - scan = heap_beginscan(rel, snapshot, 0, NULL); + scan = heap_beginscan_catalog(rel, 0, NULL); while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL) { Oid dsttablespace = HeapTupleGetOid(tuple); @@ -1810,7 +1772,6 @@ remove_dbtablespaces(Oid db_id) heap_endscan(scan); heap_close(rel, AccessShareLock); - UnregisterSnapshot(snapshot); } /* @@ -1832,19 +1793,9 @@ check_db_file_conflict(Oid db_id) Relation rel; HeapScanDesc scan; HeapTuple tuple; - Snapshot snapshot; - - /* - * As in createdb(), we'd better use an MVCC snapshot here; missing a - * tablespace could result in falsely reporting the OID is unique, with - * disastrous future consequences per the comment above. - * - * XXX change this when a generic fix for SnapshotNow races is implemented - */ - snapshot = RegisterSnapshot(GetLatestSnapshot()); rel = heap_open(TableSpaceRelationId, AccessShareLock); - scan = heap_beginscan(rel, snapshot, 0, NULL); + scan = heap_beginscan_catalog(rel, 0, NULL); while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL) { Oid dsttablespace = HeapTupleGetOid(tuple); @@ -1870,7 +1821,6 @@ check_db_file_conflict(Oid db_id) heap_endscan(scan); heap_close(rel, AccessShareLock); - UnregisterSnapshot(snapshot); return result; } @@ -1927,7 +1877,7 @@ get_database_oid(const char *dbname, bool missing_ok) BTEqualStrategyNumber, F_NAMEEQ, CStringGetDatum(dbname)); scan = systable_beginscan(pg_database, DatabaseNameIndexId, true, - SnapshotNow, 1, entry); + NULL, 1, entry); dbtuple = systable_getnext(scan); |