Allocate oids sequentially from random starting points so as not to

defeat FileStorage's index optimization.

src/ZODB/DemoStorage.py

@@ -69,6 +69,8 @@ class DemoStorage(object):
 
         self._copy_methods_from_changes(changes)
 
+        self._next_oid = random.randint(1, 1<<62)
+
     def _blobify(self):
         if (self._temporary_changes and
             isinstance(self.changes, ZODB.MappingStorage.MappingStorage)
@@ -183,26 +185,19 @@ class DemoStorage(object):
     @ZODB.utils.locked
     def new_oid(self):
         while 1:
-            oid = ZODB.utils.p64(random.randint(1, 9223372036854775807))
-
-            if oid in self._issued_oids:
-                continue
-
-            try:
-                self.changes.load(oid, '')
-            except ZODB.POSException.POSKeyError:
-                pass
-            else:
-                continue
-            try:
-                self.base.load(oid, '')
-            except ZODB.POSException.POSKeyError:
-                pass
-            else:
-                continue
-            
-            self._issued_oids.add(oid)
-            return oid
+            oid = ZODB.utils.p64(self._next_oid )
+            if oid not in self._issued_oids:
+                try:
+                    self.changes.load(oid, '')
+                except ZODB.POSException.POSKeyError:
+                    try:
+                        self.base.load(oid, '')
+                    except ZODB.POSException.POSKeyError:
+                        self._next_oid += 1
+                        self._issued_oids.add(oid)
+                        return oid
+
+            self._next_oid = random.randint(1, 1<<62)
 
     def pack(self, t, referencesf, gc=None):
         if gc is None:

src/ZODB/DemoStorage.test

@@ -96,7 +96,7 @@ the new underlying storages:
 The object id of the new object is quite random, and typically large:
 
     >>> print u64(conn.root()['2']._p_oid)
-    7106521602475165646
+    3553260803050964942
 
 Let's look at some other methods:
 
@@ -345,7 +345,7 @@ First we'll get a single OID.
     >>> storage = DemoStorage.push(storage)
     >>> random.seed(47)
     >>> storage.new_oid()
-    '\x10\x01\xa6bZ\x12\x98\xa2'
+    '\x1a,S\xa4\xe9\xbb\x17\xbd'
 
 Then we'll force the random number generator to use the same seed for the
 subsequent call to "new_oid" and show that we get a different OID.
@@ -353,7 +353,7 @@ subsequent call to "new_oid" and show that we get a different OID.
     >>> random.seed(47)
     >>> oid = storage.new_oid()
     >>> oid
-    'A\xe6\xcb\x06W\xed\xa2\x15'
+    '\x1a,S\xa4\xe9\xbb\x17\xbe'
 
 DemoStorage keeps up with the issued OIDs to know when not to reissue them...