Simplify signature of RewriteTable

This function doesn't need the lockmode to be passed: it was being used
to lock the new heap, but that's bogus, because the only caller has
already obtained the appropriate lock on the new heap (which is
unimportant anyway, because the relation's creation is not yet committed
and so no other session can see it).

Noticed while reviewed Antonin Houska's patch to add VACUUM FULL
CONCURRENTLY.

Author: alvherre

src/backend/commands/tablecmds.c

@@ -433,7 +433,7 @@ static AlterTableCmd *ATParseTransformCmd(List **wqueue, AlteredTableInfo *tab,
 static void ATRewriteTables(AlterTableStmt *parsetree,
 							List **wqueue, LOCKMODE lockmode,
 							AlterTableUtilityContext *context);
-static void ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode);
+static void ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap);
 static AlteredTableInfo *ATGetQueueEntry(List **wqueue, Relation rel);
 static void ATSimplePermissions(AlterTableType cmdtype, Relation rel, int allowed_targets);
 static void ATSimpleRecursion(List **wqueue, Relation rel,
@@ -5901,7 +5901,7 @@ ATRewriteTables(AlterTableStmt *parsetree, List **wqueue, LOCKMODE lockmode,
 			 * modifications, and test the current data within the table
 			 * against new constraints generated by ALTER TABLE commands.
 			 */
-			ATRewriteTable(tab, OIDNewHeap, lockmode);
+			ATRewriteTable(tab, OIDNewHeap);
 
 			/*
 			 * Swap the physical files of the old and new heaps, then rebuild
@@ -5934,7 +5934,7 @@ ATRewriteTables(AlterTableStmt *parsetree, List **wqueue, LOCKMODE lockmode,
 			 */
 			if (tab->constraints != NIL || tab->verify_new_notnull ||
 				tab->partition_constraint != NULL)
-				ATRewriteTable(tab, InvalidOid, lockmode);
+				ATRewriteTable(tab, InvalidOid);
 
 			/*
 			 * If we had SET TABLESPACE but no reason to reconstruct tuples,
@@ -6033,10 +6033,11 @@ ATRewriteTables(AlterTableStmt *parsetree, List **wqueue, LOCKMODE lockmode,
 /*
  * ATRewriteTable: scan or rewrite one table
  *
- * OIDNewHeap is InvalidOid if we don't need to rewrite
+ * A rewrite is requested by passing a valid OIDNewHeap; in that case, caller
+ * must already hold AccessExclusiveLock on it.
  */
 static void
-ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode)
+ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap)
 {
 	Relation	oldrel;
 	Relation	newrel;
@@ -6061,7 +6062,11 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode)
 	newTupDesc = RelationGetDescr(oldrel);	/* includes all mods */
 
 	if (OidIsValid(OIDNewHeap))
-		newrel = table_open(OIDNewHeap, lockmode);
+	{
+		Assert(CheckRelationOidLockedByMe(OIDNewHeap, AccessExclusiveLock,
+										  false));
+		newrel = table_open(OIDNewHeap, NoLock);
+	}
 	else
 		newrel = NULL;