Allow any last tid to be set for empty zeo cache files.

src/CHANGES.txt

@@ -22,7 +22,7 @@ New Features
   XXX There are known issues with this implementation that need to be
   sorted out before it is "released".
 
-3.9.0a6 (2008-12-??)
+3.9.0a7 (2008-12-??)
 ====================
 
 New Features
@@ -33,6 +33,12 @@ New Features
   The ordinary file may be used outside the current transaction and
   even after the blob's database connection has been closed.
 
+Bugs Fixed
+----------
+
+- Starting ClientStorages sometimes failed with non-new but empty
+  cache files.
+
 3.9.0a6 (2008-11-30)
 ====================
 

src/ZEO/cache.py

@@ -436,7 +436,7 @@ class ClientCache(object):
     # recent tid.
     @locked
     def setLastTid(self, tid):
-        if self.tid is not None and tid <= self.tid:
+        if (self.tid is not None) and (tid <= self.tid) and self:
             raise ValueError("new last tid (%s) must be greater than "
                              "previous one (%s)" % (u64(tid),
                                                     u64(self.tid)))

src/ZEO/tests/test_cache.py

@@ -85,6 +85,9 @@ class CacheTests(ZODB.tests.util.TestCase):
         self.assertEqual(self.cache.getLastTid(), n2)
         self.cache.invalidate(n1, n3)
         self.assertEqual(self.cache.getLastTid(), n3)
+
+        # the cache complains only when it's non-empty
+        self.cache.store(n1, n3, None, 'x')
         self.assertRaises(ValueError, self.cache.setLastTid, n2)
 
     def testLoad(self):
@@ -326,6 +329,11 @@ class CacheTests(ZODB.tests.util.TestCase):
             cache.close()
             os.remove('cache')
 
+    def testSetAnyLastTidOnEmptyCache(self):
+        self.cache.setLastTid(p64(5))
+        self.cache.setLastTid(p64(5))
+        self.cache.setLastTid(p64(3))
+        self.cache.setLastTid(p64(4))
 
 __test__ = dict(
     kill_does_not_cause_cache_corruption =