We should actually be releasing new_instance() storages, not closing …

…them. closing can impact other MVCC storages.

src/ZODB/DB.py

@@ -1066,7 +1066,11 @@ def abort(self, transaction):
 
     def close(self):
         if self._storage is not None:
-            self._storage.close()
+            # We actually want to release the storage we've created,
+            # not close it. releasing it frees external resources
+            # dedicated to this instance, closing might make permanent
+            # changes that affect other instances.
+            self._storage.release()
             self._storage = None
 
     def tpc_begin(self, transaction):

src/ZODB/tests/testDB.py

@@ -119,6 +119,7 @@ def _makeOne(self):
         class MockStorage(object):
             instance_count = 0
             close_count = 0
+            release_count = 0
             begin_count = 0
             abort_count = 0
 
@@ -132,6 +133,9 @@ def tpc_begin(self, tx):
             def close(self):
                 self.close_count += 1
 
+            def release(self):
+                self.release_count += 1
+
             def sortKey(self):
                 return 'MockStorage'
 
@@ -165,11 +169,13 @@ def test_close_many(self):
         undo.close()
         # Not open, didn't go through
         self.assertEqual(0, undo._db.storage.close_count)
+        self.assertEqual(0, undo._db.storage.release_count)
 
         undo.tpc_begin(transaction.get())
         undo.close()
         undo.close()
-        self.assertEqual(1, undo._db.storage.close_count)
+        self.assertEqual(0, undo._db.storage.close_count)
+        self.assertEqual(1, undo._db.storage.release_count)
         self.assertIsNone(undo._storage)
 
     def test_sortKey(self):
@@ -187,28 +193,32 @@ def test_tpc_abort_closes(self):
         undo.tpc_begin(transaction.get())
         undo._db.storage.tpc_abort = lambda tx: None
         undo.tpc_abort(transaction.get())
-        self.assertEqual(1, undo._db.storage.close_count)
+        self.assertEqual(0, undo._db.storage.close_count)
+        self.assertEqual(1, undo._db.storage.release_count)
 
     def test_tpc_abort_closes_on_exception(self):
         undo = self._makeOne()
         undo.tpc_begin(transaction.get())
         with self.assertRaises(AttributeError):
             undo.tpc_abort(transaction.get())
-        self.assertEqual(1, undo._db.storage.close_count)
+        self.assertEqual(0, undo._db.storage.close_count)
+        self.assertEqual(1, undo._db.storage.release_count)
 
     def test_tpc_finish_closes(self):
         undo = self._makeOne()
         undo.tpc_begin(transaction.get())
         undo._db.storage.tpc_finish = lambda tx: None
         undo.tpc_finish(transaction.get())
-        self.assertEqual(1, undo._db.storage.close_count)
+        self.assertEqual(0, undo._db.storage.close_count)
+        self.assertEqual(1, undo._db.storage.release_count)
 
     def test_tpc_finish_closes_on_exception(self):
         undo = self._makeOne()
         undo.tpc_begin(transaction.get())
         with self.assertRaises(AttributeError):
             undo.tpc_finish(transaction.get())
-        self.assertEqual(1, undo._db.storage.close_count)
+        self.assertEqual(0, undo._db.storage.close_count)
+        self.assertEqual(1, undo._db.storage.release_count)
 
 
 def test_invalidateCache():