[SPARK-4841] fix zip with textFile()

UTF8Deserializer can not be used in BatchedSerializer, so always use PickleSerializer() when change batchSize in zip().

Also, if two RDD have the same batch size already, they did not need re-serialize any more.

Author: Davies Liu <davies@databricks.com>

Closes #3706 from davies/fix_4841 and squashes the following commits:

20ce3a3 [Davies Liu] fix bug in _reserialize()
e3ebf7c [Davies Liu] add comment
379d2c8 [Davies Liu] fix zip with textFile()

(cherry picked from commit c246b95dd2f565043db429c38c6cc029a0b870c1)
Signed-off-by: Josh Rosen <joshrosen@databricks.com>

3 files changed, 26 insertions, 14 deletions

diff --git a/python/pyspark/rdd.py b/python/pyspark/rdd.py
index 57754776fa..bd2ff00c0f 100644
--- a/python/pyspark/rdd.py
+++ b/python/pyspark/rdd.py
@@ -469,8 +469,7 @@ class RDD(object):
     def _reserialize(self, serializer=None):
         serializer = serializer or self.ctx.serializer
         if self._jrdd_deserializer != serializer:
-            if not isinstance(self, PipelinedRDD):
-                self = self.map(lambda x: x, preservesPartitioning=True)
+            self = self.map(lambda x: x, preservesPartitioning=True)
             self._jrdd_deserializer = serializer
         return self
 
@@ -1798,23 +1797,21 @@ class RDD(object):
         def get_batch_size(ser):
             if isinstance(ser, BatchedSerializer):
                 return ser.batchSize
-            return 1
+            return 1  # not batched
 
         def batch_as(rdd, batchSize):
-            ser = rdd._jrdd_deserializer
-            if isinstance(ser, BatchedSerializer):
-                ser = ser.serializer
-            return rdd._reserialize(BatchedSerializer(ser, batchSize))
+            return rdd._reserialize(BatchedSerializer(PickleSerializer(), batchSize))
 
         my_batch = get_batch_size(self._jrdd_deserializer)
         other_batch = get_batch_size(other._jrdd_deserializer)
-        # use the smallest batchSize for both of them
-        batchSize = min(my_batch, other_batch)
-        if batchSize <= 0:
-            # auto batched or unlimited
-            batchSize = 100
-        other = batch_as(other, batchSize)
-        self = batch_as(self, batchSize)
+        if my_batch != other_batch:
+            # use the smallest batchSize for both of them
+            batchSize = min(my_batch, other_batch)
+            if batchSize <= 0:
+                # auto batched or unlimited
+                batchSize = 100
+            other = batch_as(other, batchSize)
+            self = batch_as(self, batchSize)
 
         if self.getNumPartitions() != other.getNumPartitions():
             raise ValueError("Can only zip with RDD which has the same number of partitions")
diff --git a/python/pyspark/serializers.py b/python/pyspark/serializers.py
index 33aa55f7f1..bd08c9a6d2 100644
--- a/python/pyspark/serializers.py
+++ b/python/pyspark/serializers.py
@@ -463,6 +463,9 @@ class CompressedSerializer(FramedSerializer):
     def loads(self, obj):
         return self.serializer.loads(zlib.decompress(obj))
 
+    def __eq__(self, other):
+        return isinstance(other, CompressedSerializer) and self.serializer == other.serializer
+
 
 class UTF8Deserializer(Serializer):
 
@@ -489,6 +492,9 @@ class UTF8Deserializer(Serializer):
         except EOFError:
             return
 
+    def __eq__(self, other):
+        return isinstance(other, UTF8Deserializer) and self.use_unicode == other.use_unicode
+
 
 def read_long(stream):
     length = stream.read(8)
diff --git a/python/pyspark/tests.py b/python/pyspark/tests.py
index 32645778c2..bca52a7ce6 100644
--- a/python/pyspark/tests.py
+++ b/python/pyspark/tests.py
@@ -533,6 +533,15 @@ class RDDTests(ReusedPySparkTestCase):
         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)])
+        # regression test for SPARK-4841
+        path = os.path.join(SPARK_HOME, "python/test_support/hello.txt")
+        t = self.sc.textFile(path)
+        cnt = t.count()
+        self.assertEqual(cnt, t.zip(t).count())
+        rdd = t.map(str)
+        self.assertEqual(cnt, t.zip(rdd).count())
+        # regression test for bug in _reserializer()
+        self.assertEqual(cnt, t.zip(rdd).count())
 
     def test_zip_with_different_number_of_items(self):
         a = self.sc.parallelize(range(5), 2)