--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/pyams_zodbbrowser/cache.py	Wed Mar 11 12:27:00 2015 +0100
@@ -0,0 +1,59 @@
+#
+# Copyright (c) 2008-2015 Thierry Florac <tflorac AT ulthar.net>
+# 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.
+#
+
+__docformat__ = 'restructuredtext'
+
+
+# import standard library
+import time
+import weakref
+
+# import interfaces
+
+# import packages
+
+
+MINUTES = 60
+HOURS = 60 * MINUTES
+
+STORAGE_TIDS = weakref.WeakKeyDictionary()
+
+
+def expired(cache_dict, cache_for):
+    if 'last_update' not in cache_dict:
+        return True
+    return time.time() > cache_dict['last_update'] + cache_for
+
+
+def getStorageTids(storage, cache_for=5 * MINUTES):
+    cache_dict = STORAGE_TIDS.setdefault(storage, {})
+    if expired(cache_dict, cache_for):
+        if cache_dict.get('tids'):
+            first = cache_dict['tids'][-1]
+            last = cache_dict['tids'][-1]
+            try:
+                first_record = next(storage.iterator())
+            except StopIteration:
+                first_record = None
+            if first_record and first_record.tid == first:
+                # okay, look for new transactions appended at the end
+                new = [t.tid for t in storage.iterator(start=last)]
+                if new and new[0] == last:
+                    del new[0]
+                cache_dict['tids'].extend(new)
+            else:
+                # first record changed, we must've packed the DB
+                cache_dict['tids'] = [t.tid for t in storage.iterator()]
+        else:
+            cache_dict['tids'] = [t.tid for t in storage.iterator()]
+        cache_dict['last_update'] = time.time()
+    return cache_dict['tids']