[SPARK-3047] [PySpark] add an option to use str in textFileRDD

str is much efficient than unicode (both CPU and memory), it'e better to use str in textFileRDD. In order to keep compatibility, use unicode by default. (Maybe change it in the future).

use_unicode=True:

daviesliudm:~/work/spark$ time python wc.py
(u'./universe/spark/sql/core/target/java/org/apache/spark/sql/execution/ExplainCommand$.java', 7776)

real	2m8.298s
user	0m0.185s
sys	0m0.064s

use_unicode=False

daviesliudm:~/work/spark$ time python wc.py
('./universe/spark/sql/core/target/java/org/apache/spark/sql/execution/ExplainCommand$.java', 7776)

real	1m26.402s
user	0m0.182s
sys	0m0.062s

We can see that it got 32% improvement!

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

Closes #1951 from davies/unicode and squashes the following commits:

8352d57 [Davies Liu] update version number
a286f2f [Davies Liu] rollback loads()
85246e5 [Davies Liu] add docs for use_unicode
a0295e1 [Davies Liu] add an option to use str in textFile()

1 files changed, 11 insertions, 7 deletions

diff --git a/python/pyspark/serializers.py b/python/pyspark/serializers.py
index 55e6cf3308..7b2710b913 100644
--- a/python/pyspark/serializers.py
+++ b/python/pyspark/serializers.py
@@ -429,18 +429,22 @@ class UTF8Deserializer(Serializer):
     Deserializes streams written by String.getBytes.
     """
 
+    def __init__(self, use_unicode=False):
+        self.use_unicode = use_unicode
+
     def loads(self, stream):
         length = read_int(stream)
-        return stream.read(length).decode('utf8')
+        s = stream.read(length)
+        return s.decode("utf-8") if self.use_unicode else s
 
     def load_stream(self, stream):
-        while True:
-            try:
+        try:
+            while True:
                 yield self.loads(stream)
-            except struct.error:
-                return
-            except EOFError:
-                return
+        except struct.error:
+            return
+        except EOFError:
+            return
 
 
 def read_long(stream):