Set cutoff xmin more aggressively when vacuuming a temporary table.

Since other sessions aren't allowed to look into a temporary table
of our own session, we do not need to worry about the global xmin
horizon when setting the vacuum XID cutoff.  Indeed, if we're not
inside a transaction block, we may set oldestXmin to be the next
XID, because there cannot be any in-doubt tuples in a temp table,
nor any tuples that are dead but still visible to some snapshot of
our transaction.  (VACUUM, of course, is never inside a transaction
block; but we need to test that because CLUSTER shares the same code.)

This approach allows us to always clean out a temp table completely
during VACUUM, independently of concurrent activity.  Aside from
being useful in its own right, that simplifies building reproducible
test cases.

Discussion: https://postgr.es/m/3490536.1598629609@sss.pgh.pa.us

1 files changed, 17 insertions, 11 deletions

diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c
index 04d12a7ece6..0d647e912c4 100644
--- a/src/backend/commands/cluster.c
+++ b/src/backend/commands/cluster.c
@@ -67,10 +67,13 @@ typedef struct
 } RelToCluster;
 
 
-static void rebuild_relation(Relation OldHeap, Oid indexOid, bool verbose);
+static void rebuild_relation(Relation OldHeap, Oid indexOid,
+							 bool isTopLevel, bool verbose);
 static void copy_table_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex,
-							bool verbose, bool *pSwapToastByContent,
-							TransactionId *pFreezeXid, MultiXactId *pCutoffMulti);
+							bool isTopLevel, bool verbose,
+							bool *pSwapToastByContent,
+							TransactionId *pFreezeXid,
+							MultiXactId *pCutoffMulti);
 static List *get_tables_to_cluster(MemoryContext cluster_context);
 
 
@@ -170,7 +173,7 @@ cluster(ClusterStmt *stmt, bool isTopLevel)
 		table_close(rel, NoLock);
 
 		/* Do the job. */
-		cluster_rel(tableOid, indexOid, stmt->options);
+		cluster_rel(tableOid, indexOid, stmt->options, isTopLevel);
 	}
 	else
 	{
@@ -219,7 +222,8 @@ cluster(ClusterStmt *stmt, bool isTopLevel)
 			PushActiveSnapshot(GetTransactionSnapshot());
 			/* Do the job. */
 			cluster_rel(rvtc->tableOid, rvtc->indexOid,
-						stmt->options | CLUOPT_RECHECK);
+						stmt->options | CLUOPT_RECHECK,
+						isTopLevel);
 			PopActiveSnapshot();
 			CommitTransactionCommand();
 		}
@@ -250,7 +254,7 @@ cluster(ClusterStmt *stmt, bool isTopLevel)
  * and error messages should refer to the operation as VACUUM not CLUSTER.
  */
 void
-cluster_rel(Oid tableOid, Oid indexOid, int options)
+cluster_rel(Oid tableOid, Oid indexOid, int options, bool isTopLevel)
 {
 	Relation	OldHeap;
 	bool		verbose = ((options & CLUOPT_VERBOSE) != 0);
@@ -400,7 +404,7 @@ cluster_rel(Oid tableOid, Oid indexOid, int options)
 	TransferPredicateLocksToHeapRelation(OldHeap);
 
 	/* rebuild_relation does all the dirty work */
-	rebuild_relation(OldHeap, indexOid, verbose);
+	rebuild_relation(OldHeap, indexOid, isTopLevel, verbose);
 
 	/* NB: rebuild_relation does table_close() on OldHeap */
 
@@ -545,11 +549,12 @@ mark_index_clustered(Relation rel, Oid indexOid, bool is_internal)
  *
  * OldHeap: table to rebuild --- must be opened and exclusive-locked!
  * indexOid: index to cluster by, or InvalidOid to rewrite in physical order.
+ * isTopLevel: should be passed down from ProcessUtility.
  *
  * NB: this routine closes OldHeap at the right time; caller should not.
  */
 static void
-rebuild_relation(Relation OldHeap, Oid indexOid, bool verbose)
+rebuild_relation(Relation OldHeap, Oid indexOid, bool isTopLevel, bool verbose)
 {
 	Oid			tableOid = RelationGetRelid(OldHeap);
 	Oid			tableSpace = OldHeap->rd_rel->reltablespace;
@@ -577,7 +582,7 @@ rebuild_relation(Relation OldHeap, Oid indexOid, bool verbose)
 							   AccessExclusiveLock);
 
 	/* Copy the heap data into the new table in the desired order */
-	copy_table_data(OIDNewHeap, tableOid, indexOid, verbose,
+	copy_table_data(OIDNewHeap, tableOid, indexOid, isTopLevel, verbose,
 					&swap_toast_by_content, &frozenXid, &cutoffMulti);
 
 	/*
@@ -728,7 +733,8 @@ make_new_heap(Oid OIDOldHeap, Oid NewTableSpace, char relpersistence,
  * *pCutoffMulti receives the MultiXactId used as a cutoff point.
  */
 static void
-copy_table_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex, bool verbose,
+copy_table_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex,
+				bool isTopLevel, bool verbose,
 				bool *pSwapToastByContent, TransactionId *pFreezeXid,
 				MultiXactId *pCutoffMulti)
 {
@@ -826,7 +832,7 @@ copy_table_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex, bool verbose,
 	 * Since we're going to rewrite the whole table anyway, there's no reason
 	 * not to be aggressive about this.
 	 */
-	vacuum_set_xid_limits(OldHeap, 0, 0, 0, 0,
+	vacuum_set_xid_limits(OldHeap, 0, 0, 0, 0, isTopLevel,
 						  &OldestXmin, &FreezeXid, NULL, &MultiXactCutoff,
 						  NULL);