Bugs Fixed

----------

- 3.10 introduced an optimization to try to address BTree conflict
  errors arrising for basing BTree keys on object ids. The
  optimization caused object ids allocated in aborted transactions to
  be reused. Unfortunately, this optimzation led to some rather
  severe failures in some applications.  The symptom is a conflict
  error in which one of the serials mentioned is zero.  This
  optimization has been removed.

src/CHANGES.txt

@@ -2,6 +2,21 @@
  Change History
 ================
 
+3.10.2 (2011-02-??)
+===================
+
+Bugs Fixed
+----------
+
+- 3.10 introduced an optimization to try to address BTree conflict
+  errors arrising for basing BTree keys on object ids. The
+  optimization caused object ids allocated in aborted transactions to
+  be reused. Unfortunately, this optimzation led to some rather
+  severe failures in some applications.  The symptom is a conflict
+  error in which one of the serials mentioned is zero.  This
+  optimization has been removed.
+
+
 3.10.1 (2010-10-27)
 ===================
 

src/ZODB/Connection.py

@@ -452,7 +452,6 @@ class Connection(ExportImport, object):
                 del obj._p_oid
                 if obj._p_changed:
                     obj._p_changed = False
-                self._db.save_oid(oid)
             else:
 
                 # Note: If we invalidate a non-ghostifiable object
@@ -760,7 +759,6 @@ class Connection(ExportImport, object):
             self._creating = {}
 
         for oid in creating:
-            self._db.save_oid(oid)
             o = self._cache.get(oid)
             if o is not None:
                 del self._cache[oid]

src/ZODB/DB.py

@@ -377,7 +377,6 @@ class DB(object):
                  database_name='unnamed',
                  databases=None,
                  xrefs=True,
-                 max_saved_oids=999,
                  large_record_size=1<<24,
                  **storage_args):
         """Create an object database.
@@ -475,8 +474,6 @@ class DB(object):
         databases[database_name] = self
         self.xrefs = xrefs
 
-        self._saved_oids = set()
-        self._max_saved_oids = max_saved_oids
         self.large_record_size = large_record_size
 
     @property
@@ -957,19 +954,7 @@ class DB(object):
     def transaction(self):
         return ContextManager(self)
 
-
-    def save_oid(self, oid):
-        if oid in self._saved_oids:
-            raise ValueError("Duplicate saved object ids.")
-        if len(self._saved_oids) < self._max_saved_oids:
-            self._saved_oids.add(oid)
-
     def new_oid(self):
-        if self._saved_oids:
-            try:
-                return self._saved_oids.pop()
-            except IndexError:
-                pass # Hm, threads
         return self.storage.new_oid()
 
 

src/ZODB/tests/new_oids_get_reused_on_abort.test

-New OIDs get reused if a transaction aborts
-===========================================
-
-Historical note:
-
-  An OID is a terrible thing to waste.
-
-  Seriously: sequential allocation of OIDs could cause problems when
-  OIDs are used as (or as the basis of) BTree keys.  This happened
-  with Zope 3's intid utility where the object->id mapping uses an
-  object key based on the OID.  We got frequent conflict errors
-  because, in a site with many users, many objects are added at the
-  same time and conficts happened when conflicting changes caused
-  bucket splits.
-
-  Reusing an earlier allocated, but discarded OID will allow retries
-  of transactions to work because they'll use earlier OIDs which won't
-  tend to conflict with newly allocated ones.
-
-If a transaction is aborted, new OIDs assigned in the transaction are
-saved and made available for later transactions.
-
-    >>> import ZODB.tests.util, transaction
-    >>> db = ZODB.tests.util.DB()
-    >>> tm1 = transaction.TransactionManager()
-    >>> conn1 = db.open(tm1)
-    >>> conn1.root.x = ZODB.tests.util.P()
-    >>> tm1.commit()
-    >>> conn1.root.x.x = ZODB.tests.util.P()
-    >>> conn1.root.y = 1
-    >>> tm2 = transaction.TransactionManager()
-    >>> conn2 = db.open(tm2)
-    >>> conn2.root.y = ZODB.tests.util.P()
-    >>> tm2.commit()
-
-We get a conflict when we try to commit the change to the first connection:
-
-    >>> tm1.commit() # doctest: +ELLIPSIS
-    Traceback (most recent call last):
-    ...
-    ConflictError: ...
-
-    >>> tm1.abort()
-
-When we try, we get the same oid we would have gotten on the first transaction:
-
-    >>> conn1.root.x.x = ZODB.tests.util.P()
-    >>> tm1.commit()
-    >>> conn1.root.x.x._p_oid
-    '\x00\x00\x00\x00\x00\x00\x00\x03'
-
-We see this more clearly when we use add to assign the oid before the commit:
-
-    >>> conn1.root.z = ZODB.tests.util.P()
-    >>> conn1.add(conn1.root.z)
-    >>> conn1.root.z._p_oid
-    '\x00\x00\x00\x00\x00\x00\x00\x04'
-
-    >>> tm1.abort()
-
-    >>> conn2.root.a = ZODB.tests.util.P()
-    >>> conn2.add(conn2.root.a)
-    >>> conn2.root.a._p_oid
-    '\x00\x00\x00\x00\x00\x00\x00\x04'

src/ZODB/tests/testConnection.py

@@ -1238,8 +1238,6 @@ class StubDatabase:
     def invalidate(self, transaction, dict_with_oid_keys, connection):
         pass
 
-    save_oid = lambda self, oid: None
-
     large_record_size = 1<<30
 
 def test_suite():

src/ZODB/tests/testConnectionSavepoint.py

@@ -180,90 +180,6 @@ the wrong state.
     """
 
 
-def testNewOidsGetReusedOnRollback():
-    """\
-    New oids assigned during a transaction should be reused on
-    rollback, not just on abort.
-
-    >>> connection = ZODB.connection(None)
-    >>> root = connection.root()
-
-    Let's make a savepoint (with a real change so that the connection
-    is involved, otherwise rolling back to the savepoint will just be
-    an abort).
-
-    >>> root._p_changed = True  # Important!
-    >>> sp = transaction.savepoint()
-
-    Add an object, and make a new savepoint so that it gets an oid.
-
-    >>> root['p'] = p = ZODB.tests.util.P()
-    >>> sp2 = transaction.savepoint()
-    >>> p._p_oid
-    '\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x01'
-
-    Rolling back to the first savepoint unassigns the oid, but not
-    before invalidating the object.  If a custom _p_invalidate method
-    tries to reactivate the object *during* rollback, a POSKeyError is
-    raised.
-
-    >>> sp.rollback()
-    >>> p._p_oid is None
-    True
-    >>> p._p_jar is None
-    True
-    >>> print p._p_changed
-    False
-
-    The rest of the state of p is undefined after the rollback.  Using
-    p in any way from this point is a bad idea.
-
-    >>> del p
-
-    If we create a new object and add it, the oid is reused.
-
-    >>> root['p'] = p = ZODB.tests.util.P()
-    >>> connection.add(p)
-    >>> p._p_oid
-    '\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x01'
-
-    >>> transaction.abort()
-    """
-
-def testNewOidNotReusedAfterRollbackOfPostAddSavepoint():
-    """\
-    >>> connection = ZODB.connection(None)
-    >>> root = connection.root()
-
-    Add an item, and make a savepoint.
-
-    >>> root['p'] = p = ZODB.tests.util.P()
-    >>> sp = transaction.savepoint()
-
-    Now rollback the savepoint.
-
-    >>> sp.rollback()
-
-    At this point, the item still exists, since it was created before
-    the savepoint we rolled back.
-
-    >>> root['p']._p_oid
-    '\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x01'
-
-    Add another item, and make another savepoint.
-
-    >>> root['p2'] = p2 = ZODB.tests.util.P()
-    >>> sp2 = transaction.savepoint()
-
-    The second item should not reuse the oid of the first.
-
-    >>> p2._p_oid
-    '\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x02'
-
-    transaction.abort()
-    """
-
-
 def tearDown(test):
     transaction.abort()
 

src/ZODB/tests/testDB.py

@@ -345,30 +345,6 @@ def minimally_test_connection_timeout():
 
     """
 
-def saving_oid_multiple_times_doesnt_cause_dups():
-    r"""Duplicate saves of an oid shouldn't happen unless there's a bug elsewhere
-
-    But saving dups makes matters worse, because it dooms the process,
-    not just the transaction.
-
-    >>> db = ZODB.DB(None)
-    >>> oid = db.new_oid()
-    >>> db.save_oid(oid)
-    >>> db.new_oid() is oid
-    True
-    >>> db.save_oid(oid)
-    >>> db.save_oid(oid)
-    Traceback (most recent call last):
-    ...
-    ValueError: Duplicate saved object ids.
-
-    >>> db.new_oid() is oid
-    True
-    >>> db.new_oid()
-    '\x00\x00\x00\x00\x00\x00\x00\x02'
-
-    """
-
 def test_suite():
     s = unittest.makeSuite(DBTests)
     s.addTest(doctest.DocTestSuite(

src/ZODB/tests/testZODB.py

@@ -18,7 +18,6 @@ from ZODB.POSException import ReadConflictError, ConflictError
 from ZODB.POSException import TransactionFailedError
 from ZODB.tests.warnhook import WarningsHook
 
-import doctest
 import transaction
 import unittest
 import warnings
@@ -615,7 +614,6 @@ class PoisonedObject:
 
 def test_suite():
     suite = unittest.makeSuite(ZODBTests, 'check')
-    suite.addTest(doctest.DocFileSuite('new_oids_get_reused_on_abort.test'))
     return suite
 
 if __name__ == "__main__":