python: idl: Clear last_id on reconnect if condition changes in-flight.

When reconnecting, if there are condition changes already sent to the
server but not yet acked, reset the db's 'last-id', esentially clearing
the local cache after reconnect.

This is needed because the client cannot easily differentiate between
the following cases:
a. either the server already processed the requested monitor
   condition change but the FSM was restarted before the
   client was notified.  In this case the client should
   clear its local cache because it's out of sync with the
   monitor view on the server side.
b. OR the server hasn't processed the requested monitor
   condition change yet.

Fixes: 46d44cf3be0d ("python: idl: Add monitor_cond_since support.")
Signed-off-by: Dumitru Ceara <dceara@redhat.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

1 files changed, 17 insertions, 1 deletions

diff --git a/python/ovs/db/idl.py b/python/ovs/db/idl.py
index 035191fc5..4ecdcaa19 100644
--- a/python/ovs/db/idl.py
+++ b/python/ovs/db/idl.py
@@ -136,6 +136,8 @@ class ConditionState(object):
             if self._new_cond is None:
                 self._new_cond = self._req_cond
             self._req_cond = None
+            return True
+        return False
 
 
 class Idl(object):
@@ -339,6 +341,19 @@ class Idl(object):
         txn-id == last_id. If there were requested condition changes in flight
         and the IDL client didn't set new conditions, then reset the requested
         conditions to new to trigger a follow-up monitor_cond_change request.
+
+        If there were changes in flight then there are two cases:
+        a. either the server already processed the requested monitor condition
+           change but the FSM was restarted before the client was notified.
+           In this case the client should clear its local cache because it's
+           out of sync with the monitor view on the server side.
+
+        b. OR the server hasn't processed the requested monitor condition
+           change yet.
+
+        As there's no easy way to differentiate between the two, and given that
+        this condition should be rare, reset the 'last_id', essentially
+        flushing the local cached DB contents.
         """
         ack_all = self.last_id == str(uuid.UUID(int=0))
         for table in self.tables.values():
@@ -346,7 +361,8 @@ class Idl(object):
                 table.condition.request()
                 table.condition.ack()
             else:
-                table.condition.reset()
+                if table.condition.reset():
+                    self.last_id = str(uuid.UUID(int=0))
                 self.cond_changed = True
 
     def restart_fsm(self):