Don't update the cache lastTid until we've invalidated a value (rather

than before).  It's possible that process shutdown after updating
lastTid but before invalidating the current record could explain some
problems we've seen on restarts.

(This change is made irrelevent by later changes.)

src/ZEO/cache.py

@@ -435,10 +435,14 @@ class ClientCache(object):
     # recent tid.
     @locked
     def setLastTid(self, tid):
+        if (not tid) or (tid == z64):
+            return
         if (self.tid is not None) and (tid <= self.tid) and self:
+            if tid == self.tid:
+                return                  # Be a little forgiving
             raise ValueError("new last tid (%s) must be greater than "
-                             "previous one (%s)" % (u64(tid),
-                                                    u64(self.tid)))
+                             "previous one (%s)"
+                             % (u64(tid), u64(self.tid)))
         assert isinstance(tid, str) and len(tid) == 8, tid
         self.tid = tid
         self.f.seek(len(magic))
@@ -647,20 +651,11 @@ class ClientCache(object):
 
     @locked
     def invalidate(self, oid, tid, server_invalidation=True):
-        if tid is not None:
-            if tid > self.tid:
-                self.setLastTid(tid)
-            elif tid < self.tid:
-                if server_invalidation:
-                    raise ValueError("invalidation tid (%s) must not be less"
-                                     " than previous one (%s)" %
-                                     (u64(tid), u64(self.tid)))
-
         ofs = self.current.get(oid)
         if ofs is None:
             # 0x10 == invalidate (miss)
             self._trace(0x10, oid, tid)
-            return
+            return self.setLastTid(tid)
 
         self.f.seek(ofs)
         read = self.f.read
@@ -683,6 +678,8 @@ class ClientCache(object):
             # 0x1C = invalidate (hit, saving non-current)
             self._trace(0x1C, oid, tid)
 
+        return self.setLastTid(tid)
+
     ##
     # Generates (oid, serial) oairs for all objects in the
     # cache.  This generator is used by cache verification.