diff --git a/transaction.py b/transaction.py
index 5e71cbe9e0..e01f938fa8 100644
--- a/transaction.py
+++ b/transaction.py
@@ -68,11 +68,13 @@ def flush(self):
 class TransactionManager(object):
     """Holds any transaction derived object list and make sure they
        are all commited, without exceeding parameters (throttling, memory consumption) """
+    DEFAULT_MAX_PARALLELISM = 5
 
-    def __init__(self, max_wait_for_replay, max_queue_size, throttling_delay):
+    def __init__(self, max_wait_for_replay, max_queue_size, throttling_delay, max_parallelism=None):
         self._MAX_WAIT_FOR_REPLAY = max_wait_for_replay
         self._MAX_QUEUE_SIZE = max_queue_size
         self._THROTTLING_DELAY = throttling_delay
+        self._MAX_PARALLELISM = max_parallelism or self.DEFAULT_MAX_PARALLELISM
 
         self._flush_without_ioloop = False # useful for tests
 
@@ -80,6 +82,7 @@ def __init__(self, max_wait_for_replay, max_queue_size, throttling_delay):
         self._total_count = 0  # Maintain size/count not to recompute it everytime
         self._total_size = 0
         self._flush_count = 0
+        self._running_flushes = 0
         self._transactions_received = 0
         self._transactions_flushed = 0
 
@@ -180,25 +183,23 @@ def flush(self):
 
     def flush_next(self):
 
-        if len(self._trs_to_flush) > 0:
-
+        if self._trs_to_flush is not None and \
+                len(self._trs_to_flush) > 0 and \
+                self._running_flushes < self._MAX_PARALLELISM:
             td = self._last_flush + self._THROTTLING_DELAY - datetime.utcnow()
-            # Python 2.7 has this built in, python < 2.7 don't...
-            if hasattr(td,'total_seconds'):
-                delay = td.total_seconds()
-            else:
-                delay = (td.microseconds + (td.seconds + td.days * 24 * 3600) * 10**6) / 10.0**6
+            delay = td.total_seconds()
 
             if delay <= 0:
                 tr = self._trs_to_flush.pop()
                 self._last_flush = datetime.utcnow()
                 log.debug("Flushing transaction %d" % tr.get_id())
                 try:
+                    self._running_flushes += 1
                     tr.flush()
-                except Exception,e :
+                except Exception as e:
                     log.exception(e)
                     self.tr_error(tr)
-                    self.flush_next()
+                self.flush_next()
             else:
                 # Wait a little bit more
                 tornado_ioloop = get_tornado_ioloop()
@@ -213,6 +214,7 @@ def flush_next(self):
             self._trs_to_flush = None
 
     def tr_error(self,tr):
+        self._running_flushes -= 1
         tr.inc_error_count()
         tr.compute_next_flush(self._MAX_WAIT_FOR_REPLAY)
         log.warn("Transaction %d in error (%s error%s), it will be replayed after %s" %
@@ -220,6 +222,7 @@ def tr_error(self,tr):
            tr.get_next_flush()))
 
     def tr_error_too_big(self,tr):
+        self._running_flushes -= 1
         tr.inc_error_count()
         log.warn("Transaction %d is %sKB, it has been rejected as too large. \
           It will not be replayed." % (tr.get_id(), tr.get_size() / 1024))
@@ -239,6 +242,7 @@ def tr_error_too_big(self,tr):
 
     def tr_success(self,tr):
         log.debug("Transaction %d completed" % tr.get_id())
+        self._running_flushes -= 1
         self._transactions.remove(tr)
         self._total_count -= 1
         self._total_size -= tr.get_size()