Spark 无法腌制 method_descriptor
Spark can't pickle method_descriptor
我收到这条奇怪的错误消息
15/01/26 13:05:12 INFO spark.SparkContext: Created broadcast 0 from wholeTextFiles at NativeMethodAccessorImpl.java:-2
Traceback (most recent call last):
File "/home/user/inverted-index.py", line 78, in <module>
print sc.wholeTextFiles(data_dir).flatMap(update).top(10)#groupByKey().map(store)
File "/home/user/spark2/python/pyspark/rdd.py", line 1045, in top
return self.mapPartitions(topIterator).reduce(merge)
File "/home/user/spark2/python/pyspark/rdd.py", line 715, in reduce
vals = self.mapPartitions(func).collect()
File "/home/user/spark2/python/pyspark/rdd.py", line 676, in collect
bytesInJava = self._jrdd.collect().iterator()
File "/home/user/spark2/python/pyspark/rdd.py", line 2107, in _jrdd
pickled_command = ser.dumps(command)
File "/home/user/spark2/python/pyspark/serializers.py", line 402, in dumps
return cloudpickle.dumps(obj, 2)
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 816, in dumps
cp.dump(obj)
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 133, in dump
return pickle.Pickler.dump(self, obj)
File "/usr/lib/python2.7/pickle.py", line 224, in dump
self.save(obj)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/usr/lib/python2.7/pickle.py", line 562, in save_tuple
save(element)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 254, in save_function
self.save_function_tuple(obj, [themodule])
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 304, in save_function_tuple
save((code, closure, base_globals))
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/usr/lib/python2.7/pickle.py", line 548, in save_tuple
save(element)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/usr/lib/python2.7/pickle.py", line 600, in save_list
self._batch_appends(iter(obj))
File "/usr/lib/python2.7/pickle.py", line 633, in _batch_appends
save(x)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 254, in save_function
self.save_function_tuple(obj, [themodule])
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 304, in save_function_tuple
save((code, closure, base_globals))
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/usr/lib/python2.7/pickle.py", line 548, in save_tuple
save(element)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/usr/lib/python2.7/pickle.py", line 600, in save_list
self._batch_appends(iter(obj))
File "/usr/lib/python2.7/pickle.py", line 633, in _batch_appends
save(x)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 254, in save_function
self.save_function_tuple(obj, [themodule])
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 304, in save_function_tuple
save((code, closure, base_globals))
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/usr/lib/python2.7/pickle.py", line 548, in save_tuple
save(element)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/usr/lib/python2.7/pickle.py", line 600, in save_list
self._batch_appends(iter(obj))
File "/usr/lib/python2.7/pickle.py", line 636, in _batch_appends
save(tmp[0])
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 249, in save_function
self.save_function_tuple(obj, modList)
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 309, in save_function_tuple
save(f_globals)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 174, in save_dict
pickle.Pickler.save_dict(self, obj)
File "/usr/lib/python2.7/pickle.py", line 649, in save_dict
self._batch_setitems(obj.iteritems())
File "/usr/lib/python2.7/pickle.py", line 681, in _batch_setitems
save(v)
File "/usr/lib/python2.7/pickle.py", line 331, in save
self.save_reduce(obj=obj, *rv)
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 650, in save_reduce
save(state)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 174, in save_dict
pickle.Pickler.save_dict(self, obj)
File "/usr/lib/python2.7/pickle.py", line 649, in save_dict
self._batch_setitems(obj.iteritems())
File "/usr/lib/python2.7/pickle.py", line 681, in _batch_setitems
save(v)
File "/usr/lib/python2.7/pickle.py", line 331, in save
self.save_reduce(obj=obj, *rv)
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 650, in save_reduce
save(state)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 174, in save_dict
pickle.Pickler.save_dict(self, obj)
File "/usr/lib/python2.7/pickle.py", line 649, in save_dict
self._batch_setitems(obj.iteritems())
File "/usr/lib/python2.7/pickle.py", line 681, in _batch_setitems
save(v)
File "/usr/lib/python2.7/pickle.py", line 331, in save
self.save_reduce(obj=obj, *rv)
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 650, in save_reduce
save(state)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 174, in save_dict
pickle.Pickler.save_dict(self, obj)
File "/usr/lib/python2.7/pickle.py", line 649, in save_dict
self._batch_setitems(obj.iteritems())
File "/usr/lib/python2.7/pickle.py", line 681, in _batch_setitems
save(v)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 547, in save_inst
self.save_inst_logic(obj)
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 537, in save_inst_logic
save(stuff)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 174, in save_dict
pickle.Pickler.save_dict(self, obj)
File "/usr/lib/python2.7/pickle.py", line 649, in save_dict
self._batch_setitems(obj.iteritems())
File "/usr/lib/python2.7/pickle.py", line 681, in _batch_setitems
save(v)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 547, in save_inst
self.save_inst_logic(obj)
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 537, in save_inst_logic
save(stuff)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 174, in save_dict
pickle.Pickler.save_dict(self, obj)
File "/usr/lib/python2.7/pickle.py", line 649, in save_dict
self._batch_setitems(obj.iteritems())
File "/usr/lib/python2.7/pickle.py", line 681, in _batch_setitems
save(v)
File "/usr/lib/python2.7/pickle.py", line 331, in save
self.save_reduce(obj=obj, *rv)
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 616, in save_reduce
save(cls)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 467, in save_global
d),obj=obj)
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 631, in save_reduce
save(args)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/usr/lib/python2.7/pickle.py", line 548, in save_tuple
save(element)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 174, in save_dict
pickle.Pickler.save_dict(self, obj)
File "/usr/lib/python2.7/pickle.py", line 649, in save_dict
self._batch_setitems(obj.iteritems())
File "/usr/lib/python2.7/pickle.py", line 681, in _batch_setitems
save(v)
File "/usr/lib/python2.7/pickle.py", line 331, in save
self.save_reduce(obj=obj, *rv)
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 616, in save_reduce
save(cls)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 442, in save_global
raise pickle.PicklingError("Can't pickle builtin %s" % obj)
pickle.PicklingError: Can't pickle builtin <type 'method_descriptor'>
我的更新函数 returns 类型为 (key, (value1, value2)) 的元组列表，它们都是字符串，如下所示：
def update(doc):
doc_id = doc[0][path_len:-ext_len] #actual file name
content = doc[1].lower()
new_fi = regex.split(content)
old_fi = fi_table.row(doc_id)
fi_table.put(doc_id, {'cf:col': ",".join(new_fi)})
if not old_fi:
return [(term, ('add', doc_id)) for term in new_fi]
else:
new_fi = set(new_fi)
old_fi = set(old_fi['cf:col'].split(','))
return [(term, ('add', doc_id)) for term in new_fi - old_fi] + \
[(term, ('del', doc_id)) for term in old_fi - new_fi]
编辑：
问题在于这 2 个 hbase 函数，行和放置。当我评论它们时，这两个代码都有效（将 old_fi 设置为空字典），但如果其中一个运行，则会产生上述错误。我在python用happybase操作hbase。谁能给我解释一下哪里出了问题？
如果这确实是 MethodDescriptorType 的 pickle 问题，您可以注册如何 pickle MethodDescriptorType，方法如下：
def _getattr(objclass, name, repr_str):
# hack to grab the reference directly
try:
attr = repr_str.split("'")[3]
return eval(attr+'.__dict__["'+name+'"]')
except:
attr = getattr(objclass,name)
if name == '__dict__':
attr = attr[name]
return attar
def save_wrapper_descriptor(pickler, obj):
pickler = Pickler(file, protocol)
pickler.save_reduce(_getattr, (obj.__objclass__, obj.__name__,
obj.__repr__()), obj=obj)
return
# register the following "type" with:
# Pickler.dispatch[MethodDescriptorType] = save_wrapper_descriptor
MethodDescriptorType = type(type.__dict__['mro'])
然后，如果将以上内容注册到 spark 使用的 pickling dispatch table（如上所示，或使用 copy_reg），它可能会通过 pickling 错误。
Spark 尝试序列化连接对象，以便它可以在执行程序内部使用，这肯定会失败，因为反序列化的数据库连接对象无法向另一个范围（甚至计算机）授予 read/write 权限。可以通过尝试广播连接对象来重现该问题。对于此实例，序列化 i/o 对象时出现问题。
问题已通过在地图函数内连接到数据库得到部分解决。由于 map 函数中每个 RDD 元素的连接太多，我不得不切换到分区处理以将数据库连接从 20k 减少到大约 8-64（基于分区数）。 Spark 开发人员应考虑为执行程序创建初始化 function/script 以避免此类死胡同问题。
所以假设我让每个节点都执行了这个 init 函数，那么每个节点都将连接到数据库（一些 conn 池，或单独的 zookeeper 节点），因为 init 函数和 map 函数将共享相同的范围，然后问题就消失了，所以你编写的代码比我找到的解决方法更快。在执行结束时，spark 将 free/unload 这些定义的变量，程序将结束。
我收到这条奇怪的错误消息
15/01/26 13:05:12 INFO spark.SparkContext: Created broadcast 0 from wholeTextFiles at NativeMethodAccessorImpl.java:-2
Traceback (most recent call last):
File "/home/user/inverted-index.py", line 78, in <module>
print sc.wholeTextFiles(data_dir).flatMap(update).top(10)#groupByKey().map(store)
File "/home/user/spark2/python/pyspark/rdd.py", line 1045, in top
return self.mapPartitions(topIterator).reduce(merge)
File "/home/user/spark2/python/pyspark/rdd.py", line 715, in reduce
vals = self.mapPartitions(func).collect()
File "/home/user/spark2/python/pyspark/rdd.py", line 676, in collect
bytesInJava = self._jrdd.collect().iterator()
File "/home/user/spark2/python/pyspark/rdd.py", line 2107, in _jrdd
pickled_command = ser.dumps(command)
File "/home/user/spark2/python/pyspark/serializers.py", line 402, in dumps
return cloudpickle.dumps(obj, 2)
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 816, in dumps
cp.dump(obj)
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 133, in dump
return pickle.Pickler.dump(self, obj)
File "/usr/lib/python2.7/pickle.py", line 224, in dump
self.save(obj)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/usr/lib/python2.7/pickle.py", line 562, in save_tuple
save(element)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 254, in save_function
self.save_function_tuple(obj, [themodule])
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 304, in save_function_tuple
save((code, closure, base_globals))
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/usr/lib/python2.7/pickle.py", line 548, in save_tuple
save(element)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/usr/lib/python2.7/pickle.py", line 600, in save_list
self._batch_appends(iter(obj))
File "/usr/lib/python2.7/pickle.py", line 633, in _batch_appends
save(x)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 254, in save_function
self.save_function_tuple(obj, [themodule])
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 304, in save_function_tuple
save((code, closure, base_globals))
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/usr/lib/python2.7/pickle.py", line 548, in save_tuple
save(element)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/usr/lib/python2.7/pickle.py", line 600, in save_list
self._batch_appends(iter(obj))
File "/usr/lib/python2.7/pickle.py", line 633, in _batch_appends
save(x)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 254, in save_function
self.save_function_tuple(obj, [themodule])
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 304, in save_function_tuple
save((code, closure, base_globals))
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/usr/lib/python2.7/pickle.py", line 548, in save_tuple
save(element)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/usr/lib/python2.7/pickle.py", line 600, in save_list
self._batch_appends(iter(obj))
File "/usr/lib/python2.7/pickle.py", line 636, in _batch_appends
save(tmp[0])
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 249, in save_function
self.save_function_tuple(obj, modList)
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 309, in save_function_tuple
save(f_globals)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 174, in save_dict
pickle.Pickler.save_dict(self, obj)
File "/usr/lib/python2.7/pickle.py", line 649, in save_dict
self._batch_setitems(obj.iteritems())
File "/usr/lib/python2.7/pickle.py", line 681, in _batch_setitems
save(v)
File "/usr/lib/python2.7/pickle.py", line 331, in save
self.save_reduce(obj=obj, *rv)
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 650, in save_reduce
save(state)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 174, in save_dict
pickle.Pickler.save_dict(self, obj)
File "/usr/lib/python2.7/pickle.py", line 649, in save_dict
self._batch_setitems(obj.iteritems())
File "/usr/lib/python2.7/pickle.py", line 681, in _batch_setitems
save(v)
File "/usr/lib/python2.7/pickle.py", line 331, in save
self.save_reduce(obj=obj, *rv)
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 650, in save_reduce
save(state)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 174, in save_dict
pickle.Pickler.save_dict(self, obj)
File "/usr/lib/python2.7/pickle.py", line 649, in save_dict
self._batch_setitems(obj.iteritems())
File "/usr/lib/python2.7/pickle.py", line 681, in _batch_setitems
save(v)
File "/usr/lib/python2.7/pickle.py", line 331, in save
self.save_reduce(obj=obj, *rv)
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 650, in save_reduce
save(state)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 174, in save_dict
pickle.Pickler.save_dict(self, obj)
File "/usr/lib/python2.7/pickle.py", line 649, in save_dict
self._batch_setitems(obj.iteritems())
File "/usr/lib/python2.7/pickle.py", line 681, in _batch_setitems
save(v)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 547, in save_inst
self.save_inst_logic(obj)
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 537, in save_inst_logic
save(stuff)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 174, in save_dict
pickle.Pickler.save_dict(self, obj)
File "/usr/lib/python2.7/pickle.py", line 649, in save_dict
self._batch_setitems(obj.iteritems())
File "/usr/lib/python2.7/pickle.py", line 681, in _batch_setitems
save(v)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 547, in save_inst
self.save_inst_logic(obj)
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 537, in save_inst_logic
save(stuff)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 174, in save_dict
pickle.Pickler.save_dict(self, obj)
File "/usr/lib/python2.7/pickle.py", line 649, in save_dict
self._batch_setitems(obj.iteritems())
File "/usr/lib/python2.7/pickle.py", line 681, in _batch_setitems
save(v)
File "/usr/lib/python2.7/pickle.py", line 331, in save
self.save_reduce(obj=obj, *rv)
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 616, in save_reduce
save(cls)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 467, in save_global
d),obj=obj)
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 631, in save_reduce
save(args)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/usr/lib/python2.7/pickle.py", line 548, in save_tuple
save(element)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 174, in save_dict
pickle.Pickler.save_dict(self, obj)
File "/usr/lib/python2.7/pickle.py", line 649, in save_dict
self._batch_setitems(obj.iteritems())
File "/usr/lib/python2.7/pickle.py", line 681, in _batch_setitems
save(v)
File "/usr/lib/python2.7/pickle.py", line 331, in save
self.save_reduce(obj=obj, *rv)
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 616, in save_reduce
save(cls)
File "/usr/lib/python2.7/pickle.py", line 286, in save
f(self, obj) # Call unbound method with explicit self
File "/home/user/spark2/python/pyspark/cloudpickle.py", line 442, in save_global
raise pickle.PicklingError("Can't pickle builtin %s" % obj)
pickle.PicklingError: Can't pickle builtin <type 'method_descriptor'>
我的更新函数 returns 类型为 (key, (value1, value2)) 的元组列表，它们都是字符串，如下所示：
def update(doc):
doc_id = doc[0][path_len:-ext_len] #actual file name
content = doc[1].lower()
new_fi = regex.split(content)
old_fi = fi_table.row(doc_id)
fi_table.put(doc_id, {'cf:col': ",".join(new_fi)})
if not old_fi:
return [(term, ('add', doc_id)) for term in new_fi]
else:
new_fi = set(new_fi)
old_fi = set(old_fi['cf:col'].split(','))
return [(term, ('add', doc_id)) for term in new_fi - old_fi] + \
[(term, ('del', doc_id)) for term in old_fi - new_fi]
编辑： 问题在于这 2 个 hbase 函数，行和放置。当我评论它们时，这两个代码都有效（将 old_fi 设置为空字典），但如果其中一个运行，则会产生上述错误。我在python用happybase操作hbase。谁能给我解释一下哪里出了问题？
如果这确实是 MethodDescriptorType 的 pickle 问题，您可以注册如何 pickle MethodDescriptorType，方法如下：
def _getattr(objclass, name, repr_str):
# hack to grab the reference directly
try:
attr = repr_str.split("'")[3]
return eval(attr+'.__dict__["'+name+'"]')
except:
attr = getattr(objclass,name)
if name == '__dict__':
attr = attr[name]
return attar
def save_wrapper_descriptor(pickler, obj):
pickler = Pickler(file, protocol)
pickler.save_reduce(_getattr, (obj.__objclass__, obj.__name__,
obj.__repr__()), obj=obj)
return
# register the following "type" with:
# Pickler.dispatch[MethodDescriptorType] = save_wrapper_descriptor
MethodDescriptorType = type(type.__dict__['mro'])
然后，如果将以上内容注册到 spark 使用的 pickling dispatch table（如上所示，或使用 copy_reg），它可能会通过 pickling 错误。
Spark 尝试序列化连接对象，以便它可以在执行程序内部使用，这肯定会失败，因为反序列化的数据库连接对象无法向另一个范围（甚至计算机）授予 read/write 权限。可以通过尝试广播连接对象来重现该问题。对于此实例，序列化 i/o 对象时出现问题。
问题已通过在地图函数内连接到数据库得到部分解决。由于 map 函数中每个 RDD 元素的连接太多，我不得不切换到分区处理以将数据库连接从 20k 减少到大约 8-64（基于分区数）。 Spark 开发人员应考虑为执行程序创建初始化 function/script 以避免此类死胡同问题。
所以假设我让每个节点都执行了这个 init 函数，那么每个节点都将连接到数据库（一些 conn 池，或单独的 zookeeper 节点），因为 init 函数和 map 函数将共享相同的范围，然后问题就消失了，所以你编写的代码比我找到的解决方法更快。在执行结束时，spark 将 free/unload 这些定义的变量，程序将结束。