Added an interface to document extra storage methods needed by ZEO.

src/ZEO/interfaces.py

+##############################################################################
+#
+# Copyright (c) 2006 Zope Corporation and Contributors.
+# All Rights Reserved.
+#
+# This software is subject to the provisions of the Zope Public License,
+# Version 2.1 (ZPL).  A copy of the ZPL should accompany this distribution.
+# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
+# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
+# FOR A PARTICULAR PURPOSE.
+#
+##############################################################################
+
+import zope.interface
+
+class IServeable(zope.interface.Interface):
+    """Interface provided by storages that can be served by ZEO
+    """
+
+    def getTid(oid):
+        """The last transaction to change an object
+
+        Return the transaction id of the last transaction that committed a
+        change to an object with the given object id.
+        
+        """
+
+    def tpc_transaction():
+        """The current transaction being committed.
+
+        If a storage is participating in a two-phase commit, then
+        return the transaction (object) being committed.  Otherwise
+        return None.
+        """
+        
+    def lastInvalidations(size):
+        """Get recent transaction invalidations
+
+        This method is optional and is used to get invalidations
+        performed by the most recent transactions.
+
+        An iterable of up to size entries must be returned, where each
+        entry is a transaction id and a sequence of object-id/version
+        pairs describing the objects and versions written by the
+        transaction, ordered starting at the most recent.
+        """