[SPARK-2790] [PySpark] fix zip with serializers which have different batch sizes.

If two RDDs have different batch size in serializers, then it will try to re-serialize the one with smaller batch size, then call RDD.zip() in Spark.

Author: Davies Liu <davies.liu@gmail.com>

Closes #1894 from davies/zip and squashes the following commits:

c4652ea [Davies Liu] add more test cases
6d05fc8 [Davies Liu] Merge branch 'master' into zip
813b1e4 [Davies Liu] add more tests for failed cases
a4aafda [Davies Liu] fix zip with serializers which have different batch sizes.

python/pyspark/rdd.py

@@ -1687,6 +1687,31 @@ class RDD(object):
         >>> x.zip(y).collect()
         [(0, 1000), (1, 1001), (2, 1002), (3, 1003), (4, 1004)]
         """
+        if self.getNumPartitions() != other.getNumPartitions():
+            raise ValueError("Can only zip with RDD which has the same number of partitions")
+
+        def get_batch_size(ser):
+            if isinstance(ser, BatchedSerializer):
+                return ser.batchSize
+            return 0
+
+        def batch_as(rdd, batchSize):
+            ser = rdd._jrdd_deserializer
+            if isinstance(ser, BatchedSerializer):
+                ser = ser.serializer
+            return rdd._reserialize(BatchedSerializer(ser, batchSize))
+
+        my_batch = get_batch_size(self._jrdd_deserializer)
+        other_batch = get_batch_size(other._jrdd_deserializer)
+        if my_batch != other_batch:
+            # use the greatest batchSize to batch the other one.
+            if my_batch > other_batch:
+                other = batch_as(other, my_batch)
+            else:
+                self = batch_as(self, other_batch)
+
+        # There will be an Exception in JVM if there are different number
+        # of items in each partitions.
         pairRDD = self._jrdd.zip(other._jrdd)
         deserializer = PairDeserializer(self._jrdd_deserializer,
                                         other._jrdd_deserializer)

python/pyspark/serializers.py

@@ -255,6 +255,9 @@ class PairDeserializer(CartesianDeserializer):
 
     def load_stream(self, stream):
         for (keys, vals) in self.prepare_keys_values(stream):
+            if len(keys) != len(vals):
+                raise ValueError("Can not deserialize RDD with different number of items"
+                                 " in pair: (%d, %d)" % (len(keys), len(vals)))
             for pair in izip(keys, vals):
                 yield pair
 

python/pyspark/tests.py

@@ -39,7 +39,7 @@ else:
 
 from pyspark.context import SparkContext
 from pyspark.files import SparkFiles
-from pyspark.serializers import read_int
+from pyspark.serializers import read_int, BatchedSerializer, MarshalSerializer, PickleSerializer
 from pyspark.shuffle import Aggregator, InMemoryMerger, ExternalMerger
 
 _have_scipy = False
@@ -339,6 +339,31 @@ class TestRDDFunctions(PySparkTestCase):
         m = self.sc.parallelize(range(1), 1).map(lambda x: len(bdata.value)).sum()
         self.assertEquals(N, m)
 
+    def test_zip_with_different_serializers(self):
+        a = self.sc.parallelize(range(5))
+        b = self.sc.parallelize(range(100, 105))
+        self.assertEqual(a.zip(b).collect(), [(0, 100), (1, 101), (2, 102), (3, 103), (4, 104)])
+        a = a._reserialize(BatchedSerializer(PickleSerializer(), 2))
+        b = b._reserialize(MarshalSerializer())
+        self.assertEqual(a.zip(b).collect(), [(0, 100), (1, 101), (2, 102), (3, 103), (4, 104)])
+
+    def test_zip_with_different_number_of_items(self):
+        a = self.sc.parallelize(range(5), 2)
+        # different number of partitions
+        b = self.sc.parallelize(range(100, 106), 3)
+        self.assertRaises(ValueError, lambda: a.zip(b))
+        # different number of batched items in JVM
+        b = self.sc.parallelize(range(100, 104), 2)
+        self.assertRaises(Exception, lambda: a.zip(b).count())
+        # different number of items in one pair
+        b = self.sc.parallelize(range(100, 106), 2)
+        self.assertRaises(Exception, lambda: a.zip(b).count())
+        # same total number of items, but different distributions
+        a = self.sc.parallelize([2, 3], 2).flatMap(range)
+        b = self.sc.parallelize([3, 2], 2).flatMap(range)
+        self.assertEquals(a.count(), b.count())
+        self.assertRaises(Exception, lambda: a.zip(b).count())
+
 
 class TestIO(PySparkTestCase):