improve log message when client cache is out of sync with server

This fixes #142

CHANGES.rst

@@ -7,6 +7,9 @@ Changelog
 - Fix data corruption due to race between load and external invalidations.
   See `issue 155 <https://github.com/zopefoundation/ZEO/issues/155>`_.
 
+- Improve logging message when client cache is out of sync with server.
+  See `issue 142 <https://github.com/zopefoundation/ZEO/issues/142>`_.
+
 5.2.2 (2020-08-11)
 ------------------
 

src/ZEO/asyncio/client.py

@@ -497,7 +497,9 @@ def verify(self, server_tid):
                 elif cache_tid > server_tid:
                     self.verify_result = "Cache newer than server"
                     logger.critical(
-                        'Client has seen newer transactions than server!')
+                        'Client cache is out of sync with the server. '
+                        'Verify that this is expected and then remove the '
+                        'cache file at %s before restarted the server.' % self.cache)
                     raise AssertionError("Server behind client, %r < %r, %s",
                                          server_tid, cache_tid, protocol)
                 elif cache_tid == server_tid: