Document an RC bug on tpc_finish.

Also, change the way TTIDs are generated in preparation for that bug's fix:
we will need TTID to be monotonous across master restarts and TID generator
provides this feature.

TODO

@@ -19,6 +19,13 @@ RC = Release Critical (for next release)
 RC  - Review XXX in the code (CODE)
 RC  - Review TODO in the code (CODE)
 RC  - Review output of pylint (CODE)
+RC  - tpc_finish might raise while transaction got successfully committed.
+      This can happen if it gets disconnected from primary master while waiting
+      for AnswerFinishTransaction after primary received it and hence will
+      commit transaction independently from client presence. Client could
+      legitimaltely think transaction is not committed, and might decide to
+      retry. To solve this, a TTID column must be added in storage nodes so
+      client can know if his TTID got successfuly committed.
     - Keep-alive (HIGH AVAILABILITY) (implemented, to be reviewed and tested)
       Consider the need to implement a keep-alive system (packets sent
       automatically when there is no activity on the connection for a period

neo/master/transactions.py

@@ -219,7 +219,6 @@ class TransactionManager(object):
         Manage current transactions
     """
     _last_tid = ZERO_TID
-    _next_ttid = 0
 
     def __init__(self, on_commit):
         # ttid -> transaction
@@ -270,18 +269,17 @@ class TransactionManager(object):
     def getLastOID(self):
         return self._last_oid
 
-    def _nextTID(self, ttid, divisor):
+    def _nextTID(self, ttid=None, divisor=None):
         """
         Compute the next TID based on the current time and check collisions.
-        Also, adjust it so that
+        Also, if ttid is not None, divisor is mandatory adjust it so that
             tid % divisor == ttid % divisor
         while preserving
             min_tid < tid
+        If ttid is None, divisor is ignored.
         When constraints allow, prefer decreasing generated TID, to avoid
         fast-forwarding to future dates.
         """
-        assert isinstance(ttid, basestring), repr(ttid)
-        assert isinstance(divisor, (int, long)), repr(divisor)
         tm = time()
         gmt = gmtime(tm)
         # See leap second handling in epoch:
@@ -299,6 +297,9 @@ class TransactionManager(object):
             try_decrease = False
         else:
             try_decrease = True
+        if ttid is not None:
+            assert isinstance(ttid, basestring), repr(ttid)
+            assert isinstance(divisor, (int, long)), repr(divisor)
             ref_remainder = u64(ttid) % divisor
             remainder = u64(tid) % divisor
             if ref_remainder != remainder:
@@ -329,14 +330,6 @@ class TransactionManager(object):
         """
         self._last_tid = max(self._last_tid, tid)
 
-    def getTTID(self):
-        """
-            Generate a temporary TID, to be used only during a single node's
-            2PC.
-        """
-        self._next_ttid += 1
-        return p64(self._next_ttid)
-
     def reset(self):
         """
             Discard all manager content
@@ -367,7 +360,7 @@ class TransactionManager(object):
         """
         if tid is None:
             # No TID requested, generate a temporary one
-            ttid = self.getTTID()
+            ttid = self._nextTID()
         else:
             # Use of specific TID requested, queue it immediately and update
             # last TID.