[SPARK-4548] []SPARK-4517] improve performance of python broadcast

Re-implement the Python broadcast using file:

1) serialize the python object using cPickle, write into disks.
2) Create a wrapper in JVM (for the dumped file), it read data from during serialization
3) Using TorrentBroadcast or HttpBroadcast to transfer the data (compressed) into executors
4) During deserialization, writing the data into disk.
5) Passing the path into Python worker, read data from disk and unpickle it into python object, until the first access.

It fixes the performance regression introduced in #2659, has similar performance as 1.1, but support object larger than 2G, also improve the memory efficiency (only one compressed copy in driver and executor).

Testing with a 500M broadcast and 4 tasks (excluding the benefit from reused worker in 1.2):

         name |   1.1   | 1.2 with this patch |  improvement
---------|--------|---------|--------
      python-broadcast-w-bytes  |	25.20  |	9.33   |	170.13% |
        python-broadcast-w-set	  |     4.13	   |    4.50  |	-8.35%  |

Testing with 100 tasks (16 CPUs):

         name |   1.1   | 1.2 with this patch |  improvement
---------|--------|---------|--------
     python-broadcast-w-bytes	| 38.16	| 8.40	 | 353.98%
        python-broadcast-w-set	| 23.29	| 9.59 |	142.80%

Author: Davies Liu <davies@databricks.com>

Closes #3417 from davies/pybroadcast and squashes the following commits:

50a58e0 [Davies Liu] address comments
b98de1d [Davies Liu] disable gc while unpickle
e5ee6b9 [Davies Liu] support large string
09303b8 [Davies Liu] read all data into memory
dde02dd [Davies Liu] improve performance of python broadcast

1 files changed, 7 insertions, 171 deletions

diff --git a/python/pyspark/serializers.py b/python/pyspark/serializers.py
index 760a509f0e..33aa55f7f1 100644
--- a/python/pyspark/serializers.py
+++ b/python/pyspark/serializers.py
@@ -448,184 +448,20 @@ class AutoSerializer(FramedSerializer):
             raise ValueError("invalid sevialization type: %s" % _type)
 
 
-class SizeLimitedStream(object):
-    """
-    Read at most `limit` bytes from underlying stream
-
-    >>> from StringIO import StringIO
-    >>> io = StringIO()
-    >>> io.write("Hello world")
-    >>> io.seek(0)
-    >>> lio = SizeLimitedStream(io, 5)
-    >>> lio.read()
-    'Hello'
-    """
-    def __init__(self, stream, limit):
-        self.stream = stream
-        self.limit = limit
-
-    def read(self, n=0):
-        if n > self.limit or n == 0:
-            n = self.limit
-        buf = self.stream.read(n)
-        self.limit -= len(buf)
-        return buf
-
-
-class CompressedStream(object):
-    """
-    Compress the data using zlib
-
-    >>> from StringIO import StringIO
-    >>> io = StringIO()
-    >>> wio = CompressedStream(io, 'w')
-    >>> wio.write("Hello world")
-    >>> wio.flush()
-    >>> io.seek(0)
-    >>> rio = CompressedStream(io, 'r')
-    >>> rio.read()
-    'Hello world'
-    >>> rio.read()
-    ''
-    """
-    MAX_BATCH = 1 << 20  # 1MB
-
-    def __init__(self, stream, mode='w', level=1):
-        self.stream = stream
-        self.mode = mode
-        if mode == 'w':
-            self.compresser = zlib.compressobj(level)
-        elif mode == 'r':
-            self.decompresser = zlib.decompressobj()
-            self.buf = ''
-        else:
-            raise ValueError("can only support mode 'w' or 'r' ")
-
-    def write(self, buf):
-        assert self.mode == 'w', "It's not opened for write"
-        if len(buf) > self.MAX_BATCH:
-            # zlib can not compress string larger than 2G
-            batches = len(buf) / self.MAX_BATCH + 1  # last one may be empty
-            for i in xrange(batches):
-                self.write(buf[i * self.MAX_BATCH:(i + 1) * self.MAX_BATCH])
-        else:
-            compressed = self.compresser.compress(buf)
-            self.stream.write(compressed)
-
-    def flush(self, mode=zlib.Z_FULL_FLUSH):
-        if self.mode == 'w':
-            d = self.compresser.flush(mode)
-            self.stream.write(d)
-            self.stream.flush()
-
-    def close(self):
-        if self.mode == 'w':
-            self.flush(zlib.Z_FINISH)
-            self.stream.close()
-
-    def read(self, size=0):
-        assert self.mode == 'r', "It's not opened for read"
-        if not size:
-            data = self.stream.read()
-            result = self.decompresser.decompress(data)
-            last = self.decompresser.flush()
-            return self.buf + result + last
-
-        # fast path for small read()
-        if size <= len(self.buf):
-            result = self.buf[:size]
-            self.buf = self.buf[size:]
-            return result
-
-        result = [self.buf]
-        size -= len(self.buf)
-        self.buf = ''
-        while size:
-            need = min(size, self.MAX_BATCH)
-            input = self.stream.read(need)
-            if input:
-                buf = self.decompresser.decompress(input)
-            else:
-                buf = self.decompresser.flush()
-
-            if len(buf) >= size:
-                self.buf = buf[size:]
-                result.append(buf[:size])
-                return ''.join(result)
-
-            size -= len(buf)
-            result.append(buf)
-            if not input:
-                return ''.join(result)
-
-    def readline(self):
-        """
-        This is needed for pickle, but not used in protocol 2
-        """
-        line = []
-        b = self.read(1)
-        while b and b != '\n':
-            line.append(b)
-            b = self.read(1)
-        line.append(b)
-        return ''.join(line)
-
-
-class LargeObjectSerializer(Serializer):
-    """
-    Serialize large object which could be larger than 2G
-
-    It uses cPickle to serialize the objects
-    """
-    def dump_stream(self, iterator, stream):
-        stream = CompressedStream(stream, 'w')
-        for value in iterator:
-            if isinstance(value, basestring):
-                if isinstance(value, unicode):
-                    stream.write('U')
-                    value = value.encode("utf-8")
-                else:
-                    stream.write('S')
-                write_long(len(value), stream)
-                stream.write(value)
-            else:
-                stream.write('P')
-                cPickle.dump(value, stream, 2)
-        stream.flush()
-
-    def load_stream(self, stream):
-        stream = CompressedStream(stream, 'r')
-        while True:
-            type = stream.read(1)
-            if not type:
-                return
-            if type in ('S', 'U'):
-                length = read_long(stream)
-                value = stream.read(length)
-                if type == 'U':
-                    value = value.decode('utf-8')
-                yield value
-            elif type == 'P':
-                yield cPickle.load(stream)
-            else:
-                raise ValueError("unknown type: %s" % type)
-
-
-class CompressedSerializer(Serializer):
+class CompressedSerializer(FramedSerializer):
     """
     Compress the serialized data
     """
     def __init__(self, serializer):
+        FramedSerializer.__init__(self)
+        assert isinstance(serializer, FramedSerializer), "serializer must be a FramedSerializer"
         self.serializer = serializer
 
-    def load_stream(self, stream):
-        stream = CompressedStream(stream, "r")
-        return self.serializer.load_stream(stream)
+    def dumps(self, obj):
+        return zlib.compress(self.serializer.dumps(obj), 1)
 
-    def dump_stream(self, iterator, stream):
-        stream = CompressedStream(stream, "w")
-        self.serializer.dump_stream(iterator, stream)
-        stream.flush()
+    def loads(self, obj):
+        return self.serializer.loads(zlib.decompress(obj))
 
 
 class UTF8Deserializer(Serializer):