refactor, add spark.shuffle.sort=False

Author: davies

python/pyspark/rdd.py

@@ -652,14 +652,13 @@ def sortByKey(self, ascending=True, numPartitions=None, keyfunc=lambda x: x):
         if numPartitions is None:
             numPartitions = self._defaultReducePartitions()
 
-        spill = (self.ctx._conf.get("spark.shuffle.spill", 'True').lower() == 'true')
-        memory = _parse_memory(self.ctx._conf.get("spark.python.worker.memory", "512m"))
+        spill = self._can_spill()
+        memory = self._memory_limit()
         serializer = self._jrdd_deserializer
 
         def sortPartition(iterator):
-            if spill:
-                sorted = ExternalSorter(memory * 0.9, serializer).sorted
-            return sorted(iterator, key=lambda (k, v): keyfunc(k), reverse=(not ascending))
+            sort = ExternalSorter(memory * 0.9, serializer).sorted if spill else sorted
+            return sort(iterator, key=lambda (k, v): keyfunc(k), reverse=(not ascending))
 
         if numPartitions == 1:
             if self.getNumPartitions() > 1:
@@ -1505,10 +1504,8 @@ def combineByKey(self, createCombiner, mergeValue, mergeCombiners,
             numPartitions = self._defaultReducePartitions()
 
         serializer = self.ctx.serializer
-        spill = (self.ctx._conf.get("spark.shuffle.spill", 'True').lower()
-                 == 'true')
-        memory = _parse_memory(self.ctx._conf.get(
-            "spark.python.worker.memory", "512m"))
+        spill = self._can_spill()
+        memory = self._memory_limit()
         agg = Aggregator(createCombiner, mergeValue, mergeCombiners)
 
         def combineLocally(iterator):
@@ -1562,7 +1559,10 @@ def createZero():
         return self.combineByKey(lambda v: func(createZero(), v), func, func, numPartitions)
 
     def _can_spill(self):
-        return (self.ctx._conf.get("spark.shuffle.spill", 'True').lower() == 'true')
+        return self.ctx._conf.get("spark.shuffle.spill", "True").lower() == "true"
+
+    def _sort_based(self):
+        return self.ctx._conf.get("spark.shuffle.sort", "False").lower() == "true"
 
     def _memory_limit(self):
         return _parse_memory(self.ctx._conf.get("spark.python.worker.memory", "512m"))
@@ -1577,6 +1577,14 @@ def groupByKey(self, numPartitions=None):
         sum or average) over each key, using reduceByKey will provide much
         better performance.
 
+        By default, it will use hash based aggregation, it can spill the items
+        into disks when the memory can not hold all the items, but it still
+        need to hold all the values for single key in memory.
+
+        When spark.shuffle.sort is True, it will switch to sort based approach,
+        then it can support single key with large number of values under small
+        amount of memory. But it is slower than hash based approach.
+
         >>> x = sc.parallelize([("a", 1), ("b", 1), ("a", 1)])
         >>> map((lambda (x,y): (x, list(y))), sorted(x.groupByKey().collect()))
         [('a', [1, 1]), ('b', [1])]
@@ -1592,9 +1600,13 @@ def mergeCombiners(a, b):
             a.extend(b)
             return a
 
-        serializer = self._jrdd_deserializer
         spill = self._can_spill()
+        sort_based = self._sort_based()
+        if sort_based and not spill:
+            raise ValueError("can not use sort based group when"
+                             " spark.executor.spill is false")
         memory = self._memory_limit()
+        serializer = self._jrdd_deserializer
         agg = Aggregator(createCombiner, mergeValue, mergeCombiners)
 
         def combineLocally(iterator):
@@ -1608,16 +1620,21 @@ def combineLocally(iterator):
         shuffled = locally_combined.partitionBy(numPartitions)
 
         def groupByKey(it):
-            if spill:
+            if sort_based:
                 # Flatten the combined values, so it will not consume huge
                 # memory during merging sort.
-                serializer = FlattedValuesSerializer(
+                ser = FlattedValuesSerializer(
                     BatchedSerializer(PickleSerializer(), 1024), 10)
-                sorted = ExternalSorter(memory * 0.9, serializer).sorted
+                sorter = ExternalSorter(memory * 0.9, ser)
+                it = sorter.sorted(it, key=operator.itemgetter(0))
+                return imap(lambda (k, v): ResultIterable(v), GroupByKey(it))
 
-            it = sorted(it, key=operator.itemgetter(0))
-            for k, v in GroupByKey(it):
-                yield k, ResultIterable(v)
+            else:
+                # this is faster than sort based
+                merger = ExternalMerger(agg, memory * 0.9, serializer) \
+                    if spill else InMemoryMerger(agg)
+                merger.mergeCombiners(it)
+                return merger.iteritems()
 
         return shuffled.mapPartitions(groupByKey)