Improve behavior of concurrent ALTER TABLE, and do some refactoring.

ALTER TABLE (and ALTER VIEW, ALTER SEQUENCE, etc.) now use a
RangeVarGetRelid callback to check permissions before acquiring a table
lock.  We also now use the same callback for all forms of ALTER TABLE,
rather than having separate, almost-identical callbacks for ALTER TABLE
.. SET SCHEMA and ALTER TABLE .. RENAME, and no callback at all for
everything else.

I went ahead and changed the code so that no form of ALTER TABLE works
on foreign tables; you must use ALTER FOREIGN TABLE instead.  In 9.1,
it was possible to use ALTER TABLE .. SET SCHEMA or ALTER TABLE ..
RENAME on a foreign table, but not any other form of ALTER TABLE, which
did not seem terribly useful or consistent.

Patch by me; review by Noah Misch.

src/backend/commands/alter.c

@@ -192,8 +192,7 @@ ExecAlterObjectSchemaStmt(AlterObjectSchemaStmt *stmt)
 		case OBJECT_TABLE:
 		case OBJECT_VIEW:
 		case OBJECT_FOREIGN_TABLE:
-			AlterTableNamespace(stmt->relation, stmt->newschema,
-								stmt->objectType, AccessExclusiveLock);
+			AlterTableNamespace(stmt);
 			break;
 
 		case OBJECT_TSPARSER:

src/backend/tcop/utility.c

@@ -699,12 +699,23 @@ standard_ProcessUtility(Node *parsetree,
 
 		case T_AlterTableStmt:
 			{
+				AlterTableStmt *atstmt = (AlterTableStmt *) parsetree;
+				Oid			relid;
 				List	   *stmts;
 				ListCell   *l;
+				LOCKMODE	lockmode;
+
+				/*
+				 * Figure out lock mode, and acquire lock.  This also does
+				 * basic permissions checks, so that we won't wait for a lock
+				 * on (for example) a relation on which we have no
+				 * permissions.
+				 */
+				lockmode = AlterTableGetLockLevel(atstmt->cmds);
+				relid = AlterTableLookupRelation(atstmt, lockmode);
 
 				/* Run parse analysis ... */
-				stmts = transformAlterTableStmt((AlterTableStmt *) parsetree,
-												queryString);
+				stmts = transformAlterTableStmt(atstmt, queryString);
 
 				/* ... and do it */
 				foreach(l, stmts)
@@ -714,7 +725,7 @@ standard_ProcessUtility(Node *parsetree,
 					if (IsA(stmt, AlterTableStmt))
 					{
 						/* Do the table alteration proper */
-						AlterTable((AlterTableStmt *) stmt);
+						AlterTable(relid, lockmode, (AlterTableStmt *) stmt);
 					}
 					else
 					{

src/include/commands/tablecmds.h

@@ -24,7 +24,9 @@ extern Oid	DefineRelation(CreateStmt *stmt, char relkind, Oid ownerId);
 
 extern void RemoveRelations(DropStmt *drop);
 
-extern void AlterTable(AlterTableStmt *stmt);
+extern Oid	AlterTableLookupRelation(AlterTableStmt *stmt, LOCKMODE lockmode);
+
+extern void AlterTable(Oid relid, LOCKMODE lockmode, AlterTableStmt *stmt);
 
 extern LOCKMODE AlterTableGetLockLevel(List *cmds);
 
@@ -32,8 +34,7 @@ extern void ATExecChangeOwner(Oid relationOid, Oid newOwnerId, bool recursing, L
 
 extern void AlterTableInternal(Oid relid, List *cmds, bool recurse);
 
-extern void AlterTableNamespace(RangeVar *relation, const char *newschema,
-					ObjectType stmttype, LOCKMODE lockmode);
+extern void AlterTableNamespace(AlterObjectSchemaStmt *stmt);
 
 extern void AlterRelationNamespaceInternal(Relation classRel, Oid relOid,
 							   Oid oldNspOid, Oid newNspOid,