- Fixed bug that could lead to memory errors due to the use

  of a Python disctionary for a mapping that can grow large.

(Not large enough to use a lot of memory, but large enough to cause
  malloc to fail. :()

NEWS.txt

@@ -5,7 +5,10 @@ Whats new in ZODB 3.8.1
 
 Bugs Fixed:
 
-- (???) Fixed bug #251037: Made packing of blob storages non-blocking.
+- (beta 7) Fixed bug that could lead to memory errors due to the use
+  of a Python disctionary for a mapping that can grow large.
+
+- (beta 7) Fixed bug #251037: Made packing of blob storages non-blocking.
 
 - (beta 6) Fixed a bug that could cause InvalidObjectReference errors
   for objects that were explicitly added to a database if the object

src/ZODB/FileStorage/FileStorage.py

@@ -43,6 +43,8 @@ from ZODB.FileStorage.format import CorruptedDataError
 from ZODB.loglevels import BLATHER
 from ZODB.fsIndex import fsIndex
 
+import BTrees.OOBTree
+
 packed_version = "FS21"
 
 logger = logging.getLogger('ZODB.FileStorage')
@@ -229,7 +231,7 @@ class FileStorage(BaseStorage.BaseStorage,
 
     def _newIndexes(self):
         # hook to use something other than builtin dict
-        return fsIndex(), {}, {}, {}, {}, {}, {}
+        return fsIndex(), {}, {}, {}, BTrees.OOBTree.OOBTree(), {}, {}
 
     _saved = 0
     def _save_index(self):