Comment about backup limitations

TODO

@@ -85,6 +85,11 @@ RC  - Review output of pylint (CODE)
       Currently, storage presence is broadcasted to client nodes too early, as
       the storage node would refuse them until it has only up-to-date data (not
       only up-to-date cells, but also a partition table and node states).
+    - In backup mode, 2 simultaneous replication should be possible so that:
+      - outdated cells does not block backup for too long time
+      - constantly modified partitions does not prevent outdated cells to
+        replicate
+      Current behaviour is undefined and the above 2 scenarios may happen.
     - Create a specialized PartitionTable that know the database and replicator
       to remove duplicates and remove logic from handlers (CODE)
     - Consider insert multiple objects at time in the database, with taking care

neo/master/backup_app.py

@@ -141,6 +141,9 @@ class BackupApplication(object):
                 tid = app.backup_tid
                 # Wait for non-primary partitions to catch up,
                 # so that all UP_TO_DATE cells are really UP_TO_DATE.
+                # XXX: Another possibility could be to outdate such cells, and
+                #      they would be quickly updated at the beginning of the
+                #      RUNNING phase. This may simplify code.
                 # Any unfinished replication from upstream will be truncated.
                 while pt.getCheckTid(xrange(pt.getPartitions())) < tid:
                     poll(1)

neo/storage/replicator.py

@@ -227,6 +227,8 @@ class Replicator(object):
             return
         app = self.app
         # Choose a partition with no unfinished transaction if possible.
+        # XXX: When leaving backup mode, we should only consider UP_TO_DATE
+        #      cells when leaving backup mode.
         for offset in self.replicate_dict:
             if not self.partition_dict[offset].max_ttid:
                 break