#
# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements. See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License. You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
"""
PySpark supports custom serializers for transferring data; this can improve
performance.
By default, PySpark uses L{PickleSerializer} to serialize objects using Python's
C{cPickle} serializer, which can serialize nearly any Python object.
Other serializers, like L{MarshalSerializer}, support fewer datatypes but can be
faster.
The serializer is chosen when creating L{SparkContext}:
>>> from pyspark.context import SparkContext
>>> from pyspark.serializers import MarshalSerializer
>>> sc = SparkContext('local', 'test', serializer=MarshalSerializer())
>>> sc.parallelize(list(range(1000))).map(lambda x: 2 * x).take(10)
[0, 2, 4, 6, 8, 10, 12, 14, 16, 18]
>>> sc.stop()
PySpark serialize objects in batches; By default, the batch size is chosen based
on the size of objects, also configurable by SparkContext's C{batchSize} parameter:
>>> sc = SparkContext('local', 'test', batchSize=2)
>>> rdd = sc.parallelize(range(16), 4).map(lambda x: x)
Behind the scenes, this creates a JavaRDD with four partitions, each of
which contains two batches of two objects:
>>> rdd.glom().collect()
[[0, 1, 2, 3], [4, 5, 6, 7], [8, 9, 10, 11], [12, 13, 14, 15]]
>>> int(rdd._jrdd.count())
8
>>> sc.stop()
"""
import sys
from itertools import chain, product
import marshal
import struct
import types
import collections
import zlib
import itertools
if sys.version < '3':
import cPickle as pickle
protocol = 2
from itertools import izip as zip, imap as map
else:
import pickle
protocol = 3
xrange = range
from pyspark import cloudpickle
__all__ = ["PickleSerializer", "MarshalSerializer", "UTF8Deserializer"]
class SpecialLengths(object):
END_OF_DATA_SECTION = -1
PYTHON_EXCEPTION_THROWN = -2
TIMING_DATA = -3
END_OF_STREAM = -4
NULL = -5
class Serializer(object):
def dump_stream(self, iterator, stream):
"""
Serialize an iterator of objects to the output stream.
"""
raise NotImplementedError
def load_stream(self, stream):
"""
Return an iterator of deserialized objects from the input stream.
"""
raise NotImplementedError
def _load_stream_without_unbatching(self, stream):
"""
Return an iterator of deserialized batches (iterable) of objects from the input stream.
if the serializer does not operate on batches the default implementation returns an
iterator of single element lists.
"""
return map(lambda x: [x], self.load_stream(stream))
# Note: our notion of "equality" is that output generated by
# equal serializers can be deserialized using the same serializer.
# This default implementation handles the simple cases;
# subclasses should override __eq__ as appropriate.
def __eq__(self, other):
return isinstance(other, self.__class__) and self.__dict__ == other.__dict__
def __ne__(self, other):
return not self.__eq__(other)
def __repr__(self):
return "%s()" % self.__class__.__name__
def __hash__(self):
return hash(str(self))
class FramedSerializer(Serializer):
"""
Serializer that writes objects as a stream of (length, data) pairs,
where C{length} is a 32-bit integer and data is C{length} bytes.
"""
def __init__(self):
# On Python 2.6, we can't write bytearrays to streams, so we need to convert them
# to strings first. Check if the version number is that old.
self._only_write_strings = sys.version_info[0:2] <= (2, 6)
def dump_stream(self, iterator, stream):
for obj in iterator:
self._write_with_length(obj, stream)
def load_stream(self, stream):
while True:
try:
yield self._read_with_length(stream)
except EOFError:
return
def _write_with_length(self, obj, stream):
serialized = self.dumps(obj)
if serialized is None:
raise ValueError("serialized value should not be None")
if len(serialized) > (1 << 31):
raise ValueError("can not serialize object larger than 2G")
write_int(len(serialized), stream)
if self._only_write_strings:
stream.write(str(serialized))
else:
stream.write(serialized)
def _read_with_length(self, stream):
length = read_int(stream)
if length == SpecialLengths.END_OF_DATA_SECTION:
raise EOFError
elif length == SpecialLengths.NULL:
return None
obj = stream.read(length)
if len(obj) < length:
raise EOFError
return self.loads(obj)
def dumps(self, obj):
"""
Serialize an object into a byte array.
When batching is used, this will be called with an array of objects.
"""
raise NotImplementedError
def loads(self, obj):
"""
Deserialize an object from a byte array.
"""
raise NotImplementedError
class BatchedSerializer(Serializer):
"""
Serializes a stream of objects in batches by calling its wrapped
Serializer with streams of objects.
"""
UNLIMITED_BATCH_SIZE = -1
UNKNOWN_BATCH_SIZE = 0
def __init__(self, serializer, batchSize=UNLIMITED_BATCH_SIZE):
self.serializer = serializer
self.batchSize = batchSize
def _batched(self, iterator):
if self.batchSize == self.UNLIMITED_BATCH_SIZE:
yield list(iterator)
elif hasattr(iterator, "__len__") and hasattr(iterator, "__getslice__"):
n = len(iterator)
for i in xrange(0, n, self.batchSize):
yield iterator[i: i + self.batchSize]
else:
items = []
count = 0
for item in iterator:
items.append(item)
count += 1
if count == self.batchSize:
yield items
items = []
count = 0
if items:
yield items
def dump_stream(self, iterator, stream):
self.serializer.dump_stream(self._batched(iterator), stream)
def load_stream(self, stream):
return chain.from_iterable(self._load_stream_without_unbatching(stream))
def _load_stream_without_unbatching(self, stream):
return self.serializer.load_stream(stream)
def __repr__(self):
return "BatchedSerializer(%s, %d)" % (str(self.serializer), self.batchSize)
class FlattenedValuesSerializer(BatchedSerializer):
"""
Serializes a stream of list of pairs, split the list of values
which contain more than a certain number of objects to make them
have similar sizes.
"""
def __init__(self, serializer, batchSize=10):
BatchedSerializer.__init__(self, serializer, batchSize)
def _batched(self, iterator):
n = self.batchSize
for key, values in iterator:
for i in range(0, len(values), n):
yield key, values[i:i + n]
def load_stream(self, stream):
return self.serializer.load_stream(stream)
def __repr__(self):
return "FlattenedValuesSerializer(%s, %d)" % (self.serializer, self.batchSize)
class AutoBatchedSerializer(BatchedSerializer):
"""
Choose the size of batch automatically based on the size of object
"""
def __init__(self, serializer, bestSize=1 << 16):
BatchedSerializer.__init__(self, serializer, self.UNKNOWN_BATCH_SIZE)
self.bestSize = bestSize
def dump_stream(self, iterator, stream):
batch, best = 1, self.bestSize
iterator = iter(iterator)
while True:
vs = list(itertools.islice(iterator, batch))
if not vs:
break
bytes = self.serializer.dumps(vs)
write_int(len(bytes), stream)
stream.write(bytes)
size = len(bytes)
if size < best:
batch *= 2
elif size > best * 10 and batch > 1:
batch //= 2
def __repr__(self):
return "AutoBatchedSerializer(%s)" % self.serializer
class CartesianDeserializer(Serializer):
"""
Deserializes the JavaRDD cartesian() of two PythonRDDs.
Due to pyspark batching we cannot simply use the result of the Java RDD cartesian,
we additionally need to do the cartesian within each pair of batches.
"""
def __init__(self, key_ser, val_ser):
self.key_ser = key_ser
self.val_ser = val_ser
def _load_stream_without_unbatching(self, stream):
key_batch_stream = self.key_ser._load_stream_without_unbatching(stream)
val_batch_stream = self.val_ser._load_stream_without_unbatching(stream)
for (key_batch, val_batch) in zip(key_batch_stream, val_batch_stream):
# for correctness with repeated cartesian/zip this must be returned as one batch
yield product(key_batch, val_batch)
def load_stream(self, stream):
return chain.from_iterable(self._load_stream_without_unbatching(stream))
def __repr__(self):
return "CartesianDeserializer(%s, %s)" % \
(str(self.key_ser), str(self.val_ser))
class PairDeserializer(Serializer):
"""
Deserializes the JavaRDD zip() of two PythonRDDs.
Due to pyspark batching we cannot simply use the result of the Java RDD zip,
we additionally need to do the zip within each pair of batches.
"""
def __init__(self, key_ser, val_ser):
self.key_ser = key_ser
self.val_ser = val_ser
def _load_stream_without_unbatching(self, stream):
key_batch_stream = self.key_ser._load_stream_without_unbatching(stream)
val_batch_stream = self.val_ser._load_stream_without_unbatching(stream)
for (key_batch, val_batch) in zip(key_batch_stream, val_batch_stream):
# For double-zipped RDDs, the batches can be iterators from other PairDeserializer,
# instead of lists. We need to convert them to lists if needed.
key_batch = key_batch if hasattr(key_batch, '__len__') else list(key_batch)
val_batch = val_batch if hasattr(val_batch, '__len__') else list(val_batch)
if len(key_batch) != len(val_batch):
raise ValueError("Can not deserialize PairRDD with different number of items"
" in batches: (%d, %d)" % (len(key_batch), len(val_batch)))
# for correctness with repeated cartesian/zip this must be returned as one batch
yield zip(key_batch, val_batch)
def load_stream(self, stream):
return chain.from_iterable(self._load_stream_without_unbatching(stream))
def __repr__(self):
return "PairDeserializer(%s, %s)" % (str(self.key_ser), str(self.val_ser))
class NoOpSerializer(FramedSerializer):
def loads(self, obj):
return obj
def dumps(self, obj):
return obj
# Hook namedtuple, make it picklable
__cls = {}
def _restore(name, fields, value):
""" Restore an object of namedtuple"""
k = (name, fields)
cls = __cls.get(k)
if cls is None:
cls = collections.namedtuple(name, fields)
__cls[k] = cls
return cls(*value)
def _hack_namedtuple(cls):
""" Make class generated by namedtuple picklable """
name = cls.__name__
fields = cls._fields
def __reduce__(self):
return (_restore, (name, fields, tuple(self)))
cls.__reduce__ = __reduce__
cls._is_namedtuple_ = True
return cls
def _hijack_namedtuple():
""" Hack namedtuple() to make it picklable """
# hijack only one time
if hasattr(collections.namedtuple, "__hijack"):
return
global _old_namedtuple # or it will put in closure
global _old_namedtuple_kwdefaults # or it will put in closure too
def _copy_func(f):
return types.FunctionType(f.__code__, f.__globals__, f.__name__,
f.__defaults__, f.__closure__)
def _kwdefaults(f):
# __kwdefaults__ contains the default values of keyword-only arguments which are
# introduced from Python 3. The possible cases for __kwdefaults__ in namedtuple
# are as below:
#
# - Does not exist in Python 2.
# - Returns None in <= Python 3.5.x.
# - Returns a dictionary containing the default values to the keys from Python 3.6.x
# (See https://bugs.python.org/issue25628).
kargs = getattr(f, "__kwdefaults__", None)
if kargs is None:
return {}
else:
return kargs
_old_namedtuple = _copy_func(collections.namedtuple)
_old_namedtuple_kwdefaults = _kwdefaults(collections.namedtuple)
def namedtuple(*args, **kwargs):
for k, v in _old_namedtuple_kwdefaults.items():
kwargs[k] = kwargs.get(k, v)
cls = _old_namedtuple(*args, **kwargs)
return _hack_namedtuple(cls)
# replace namedtuple with new one
collections.namedtuple.__globals__["_old_namedtuple_kwdefaults"] = _old_namedtuple_kwdefaults
collections.namedtuple.__globals__["_old_namedtuple"] = _old_namedtuple
collections.namedtuple.__globals__["_hack_namedtuple"] = _hack_namedtuple
collections.namedtuple.__code__ = namedtuple.__code__
collections.namedtuple.__hijack = 1
# hack the cls already generated by namedtuple
# those created in other module can be pickled as normal,
# so only hack those in __main__ module
for n, o in sys.modules["__main__"].__dict__.items():
if (type(o) is type and o.__base__ is tuple
and hasattr(o, "_fields")
and "__reduce__" not in o.__dict__):
_hack_namedtuple(o) # hack inplace
_hijack_namedtuple()
[docs]class PickleSerializer(FramedSerializer):
"""
Serializes objects using Python's pickle serializer:
http://docs.python.org/2/library/pickle.html
This serializer supports nearly any Python object, but may
not be as fast as more specialized serializers.
"""
[docs] def dumps(self, obj):
return pickle.dumps(obj, protocol)
if sys.version >= '3':
def loads(self, obj, encoding="bytes"):
return pickle.loads(obj, encoding=encoding)
else:
[docs] def loads(self, obj, encoding=None):
return pickle.loads(obj)
class CloudPickleSerializer(PickleSerializer):
def dumps(self, obj):
return cloudpickle.dumps(obj, 2)
[docs]class MarshalSerializer(FramedSerializer):
"""
Serializes objects using Python's Marshal serializer:
http://docs.python.org/2/library/marshal.html
This serializer is faster than PickleSerializer but supports fewer datatypes.
"""
[docs] def dumps(self, obj):
return marshal.dumps(obj)
[docs] def loads(self, obj):
return marshal.loads(obj)
class AutoSerializer(FramedSerializer):
"""
Choose marshal or pickle as serialization protocol automatically
"""
def __init__(self):
FramedSerializer.__init__(self)
self._type = None
def dumps(self, obj):
if self._type is not None:
return b'P' + pickle.dumps(obj, -1)
try:
return b'M' + marshal.dumps(obj)
except Exception:
self._type = b'P'
return b'P' + pickle.dumps(obj, -1)
def loads(self, obj):
_type = obj[0]
if _type == b'M':
return marshal.loads(obj[1:])
elif _type == b'P':
return pickle.loads(obj[1:])
else:
raise ValueError("invalid sevialization type: %s" % _type)
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 dumps(self, obj):
return zlib.compress(self.serializer.dumps(obj), 1)
def loads(self, obj):
return self.serializer.loads(zlib.decompress(obj))
def __repr__(self):
return "CompressedSerializer(%s)" % self.serializer
class UTF8Deserializer(Serializer):
"""
Deserializes streams written by String.getBytes.
"""
def __init__(self, use_unicode=True):
self.use_unicode = use_unicode
def loads(self, stream):
length = read_int(stream)
if length == SpecialLengths.END_OF_DATA_SECTION:
raise EOFError
elif length == SpecialLengths.NULL:
return None
s = stream.read(length)
return s.decode("utf-8") if self.use_unicode else s
def load_stream(self, stream):
try:
while True:
yield self.loads(stream)
except struct.error:
return
except EOFError:
return
def __repr__(self):
return "UTF8Deserializer(%s)" % self.use_unicode
def read_long(stream):
length = stream.read(8)
if not length:
raise EOFError
return struct.unpack("!q", length)[0]
def write_long(value, stream):
stream.write(struct.pack("!q", value))
def pack_long(value):
return struct.pack("!q", value)
def read_int(stream):
length = stream.read(4)
if not length:
raise EOFError
return struct.unpack("!i", length)[0]
def write_int(value, stream):
stream.write(struct.pack("!i", value))
def read_bool(stream):
length = stream.read(1)
if not length:
raise EOFError
return struct.unpack("!?", length)[0]
def write_with_length(obj, stream):
write_int(len(obj), stream)
stream.write(obj)
class ChunkedStream(object):
"""
This file-like object takes a stream of data, of unknown length, and breaks it into fixed
length frames. The intended use case is serializing large data and sending it immediately over
a socket -- we do not want to buffer the entire data before sending it, but the receiving end
needs to know whether or not there is more data coming.
It works by buffering the incoming data in some fixed-size chunks. If the buffer is full, it
first sends the buffer size, then the data. This repeats as long as there is more data to send.
When this is closed, it sends the length of whatever data is in the buffer, then that data, and
finally a "length" of -1 to indicate the stream has completed.
"""
def __init__(self, wrapped, buffer_size):
self.buffer_size = buffer_size
self.buffer = bytearray(buffer_size)
self.current_pos = 0
self.wrapped = wrapped
def write(self, bytes):
byte_pos = 0
byte_remaining = len(bytes)
while byte_remaining > 0:
new_pos = byte_remaining + self.current_pos
if new_pos < self.buffer_size:
# just put it in our buffer
self.buffer[self.current_pos:new_pos] = bytes[byte_pos:]
self.current_pos = new_pos
byte_remaining = 0
else:
# fill the buffer, send the length then the contents, and start filling again
space_left = self.buffer_size - self.current_pos
new_byte_pos = byte_pos + space_left
self.buffer[self.current_pos:self.buffer_size] = bytes[byte_pos:new_byte_pos]
write_int(self.buffer_size, self.wrapped)
self.wrapped.write(self.buffer)
byte_remaining -= space_left
byte_pos = new_byte_pos
self.current_pos = 0
def close(self):
# if there is anything left in the buffer, write it out first
if self.current_pos > 0:
write_int(self.current_pos, self.wrapped)
self.wrapped.write(self.buffer[:self.current_pos])
# -1 length indicates to the receiving end that we're done.
write_int(-1, self.wrapped)
self.wrapped.close()
if __name__ == '__main__':
import doctest
(failure_count, test_count) = doctest.testmod()
if failure_count:
exit(-1)
