diff --git a/DAS/validator.py b/DAS/validator.py
index ba33170..88ef42a 100644
--- a/DAS/validator.py
+++ b/DAS/validator.py
@@ -3,6 +3,7 @@
 import random
 import collections
 import logging
+import sys
 from DAS.block import *
 from bitarray import bitarray
 from bitarray.util import zeros
@@ -12,6 +13,34 @@ def shuffled(lis):
     for index in random.sample(range(len(lis)), len(lis)):
         yield lis[index]
 
+def sampleLine(line, limit):
+    """ sample up to 'limit' bits from a bitarray
+
+    Since this is quite expensive, we use a number of heuristics to get it fast.
+    """
+    if limit == sys.maxsize :
+        return line
+    else:
+        w = line.count(1)
+        if limit >= w :
+            return line
+        else:
+            l = len(line)
+            r = zeros(l)
+            if w < l/10 or limit > l/2 :
+                indices = [ i for i in range(l) if line[i] ]
+                sample = random.sample(indices, limit)
+                for i in sample:
+                    r[i] = 1
+                return r
+            else:
+                while limit:
+                    i = random.randrange(0, l)
+                    if line[i] and not r[i]:
+                        r[i] = 1
+                        limit -= 1
+                return r
+
 class NextToSend:
     def __init__(self, neigh, toSend, id, dim):
         self.neigh = neigh
@@ -177,8 +206,7 @@ class Validator:
         self.statsRxInSlot = 0
         self.statsTxInSlot = 0
 
-
-    def nextColumnToSend(self, columnID):
+    def nextColumnToSend(self, columnID, limit = sys.maxsize):
         line = self.getColumn(columnID)
         if line.any():
             self.logger.debug("col %d -> %s", columnID, self.columnNeighbors[columnID] , extra=self.format)
@@ -187,9 +215,10 @@ class Validator:
                 # if there is anything new to send, send it
                 toSend = line & ~n.sent & ~n.received
                 if (toSend).any():
+                    toSend = sampleLine(toSend, limit)
                     yield NextToSend(n, toSend, columnID, 1)
 
-    def nextRowToSend(self, rowID):
+    def nextRowToSend(self, rowID, limit = sys.maxsize):
         line = self.getRow(rowID)
         if line.any():
             self.logger.debug("row %d -> %s", rowID, self.rowNeighbors[rowID], extra=self.format)
@@ -198,6 +227,7 @@ class Validator:
                 # if there is anything new to send, send it
                 toSend = line & ~n.sent & ~n.received
                 if (toSend).any():
+                    toSend = sampleLine(toSend, limit)
                     yield NextToSend(n, toSend, rowID, 0)
 
     def nextToSend(self):