Avoid duplicates in ALTER ... DEPENDS ON EXTENSION

alvherre · alvherre · commit 3dfd2d6cd28a · 2020-03-11T11:04:59.000-03:00
If the command is attempted for an extension that the object already depends on, silently do nothing. In particular, this means that if a database containing multiple such entries is dumped, the restore will silently do the right thing and record just the first one. (At least, in a world where pg_dump does dump such entries -- which it doesn't currently, but it will.) Backpatch to 9.6, where this kind of dependency was introduced. Reviewed-by: Ibrar Ahmed, Tom Lane (offlist) Discussion: https://postgr.es/m/20200217225333.GA30974@alvherre.pgsql
diff --git a/src/backend/catalog/pg_depend.c b/src/backend/catalog/pg_depend.c
@@ -485,6 +485,49 @@ getExtensionOfObject(Oid classId, Oid objectId)
 	return result;
 }
 
+/*
+ * Return (possibly NIL) list of extensions that the given object depends on
+ * in DEPENDENCY_AUTO_EXTENSION mode.
+ */
+List *
+getAutoExtensionsOfObject(Oid classId, Oid objectId)
+{
+	List	   *result = NIL;
+	Relation	depRel;
+	ScanKeyData	key[2];
+	SysScanDesc	scan;
+	HeapTuple	tup;
+
+	depRel = heap_open(DependRelationId, AccessShareLock);
+
+	ScanKeyInit(&key[0],
+				Anum_pg_depend_classid,
+				BTEqualStrategyNumber, F_OIDEQ,
+				ObjectIdGetDatum(classId));
+	ScanKeyInit(&key[1],
+				Anum_pg_depend_objid,
+				BTEqualStrategyNumber, F_OIDEQ,
+				ObjectIdGetDatum(objectId));
+
+	scan = systable_beginscan(depRel, DependDependerIndexId, true,
+							  NULL, 2, key);
+
+	while (HeapTupleIsValid((tup = systable_getnext(scan))))
+	{
+		Form_pg_depend depform = (Form_pg_depend) GETSTRUCT(tup);
+
+		if (depform->refclassid == ExtensionRelationId &&
+			depform->deptype == DEPENDENCY_AUTO_EXTENSION)
+			result = lappend_oid(result, depform->refobjid);
+	}
+
+	systable_endscan(scan);
+
+	heap_close(depRel, AccessShareLock);
+
+	return result;
+}
+
 /*
  * Detect whether a sequence is marked as "owned" by a column
  *
diff --git a/src/backend/commands/alter.c b/src/backend/commands/alter.c
@@ -425,6 +425,7 @@ ExecAlterObjectDependsStmt(AlterObjectDependsStmt *stmt, ObjectAddress *refAddre
 	ObjectAddress address;
 	ObjectAddress refAddr;
 	Relation	rel;
+	List   *currexts;
 
 	address =
 		get_object_address_rv(stmt->objectType, stmt->relation, (List *) stmt->object,
@@ -454,7 +455,11 @@ ExecAlterObjectDependsStmt(AlterObjectDependsStmt *stmt, ObjectAddress *refAddre
 	if (refAddress)
 		*refAddress = refAddr;
 
-	recordDependencyOn(&address, &refAddr, DEPENDENCY_AUTO_EXTENSION);
+	/* Avoid duplicates */
+	currexts = getAutoExtensionsOfObject(address.classId,
+										 address.objectId);
+	if (!list_member_oid(currexts, refAddr.objectId))
+		recordDependencyOn(&address, &refAddr, DEPENDENCY_AUTO_EXTENSION);
 
 	return address;
 }
diff --git a/src/include/catalog/dependency.h b/src/include/catalog/dependency.h
@@ -237,6 +237,7 @@ extern long changeDependencyFor(Oid classId, Oid objectId,
 					Oid newRefObjectId);
 
 extern Oid	getExtensionOfObject(Oid classId, Oid objectId);
+extern List *getAutoExtensionsOfObject(Oid classId, Oid objectId);
 
 extern bool sequenceIsOwned(Oid seqId, char deptype, Oid *tableId, int32 *colId);
 extern List *getOwnedSequences(Oid relid, AttrNumber attnum);
diff --git a/src/test/modules/test_extensions/expected/test_extdepend.out b/src/test/modules/test_extensions/expected/test_extdepend.out
@@ -47,6 +47,8 @@ SELECT * FROM test_extdep_commands \gexec
  CREATE INDEX e ON a (a1)
  ALTER INDEX e DEPENDS ON EXTENSION test_ext5
  RESET search_path
+-- A dependent object made dependent again has no effect
+ALTER FUNCTION test_ext.b() DEPENDS ON EXTENSION test_ext5;
 -- make sure we have the right dependencies on the extension
 SELECT deptype, p.*
   FROM pg_depend, pg_identify_object(classid, objid, objsubid) AS p
diff --git a/src/test/modules/test_extensions/sql/test_extdepend.sql b/src/test/modules/test_extensions/sql/test_extdepend.sql
@@ -27,6 +27,8 @@ COPY test_extdep_commands FROM stdin;
 SELECT * FROM test_extdep_commands;
 -- First, test that dependent objects go away when the extension is dropped.
 SELECT * FROM test_extdep_commands \gexec
+-- A dependent object made dependent again has no effect
+ALTER FUNCTION test_ext.b() DEPENDS ON EXTENSION test_ext5;
 -- make sure we have the right dependencies on the extension
 SELECT deptype, p.*
   FROM pg_depend, pg_identify_object(classid, objid, objsubid) AS p
