[SPARK-6055] [PySpark] fix incorrect __eq__ of DataType

The _eq_ of DataType is not correct, class cache is not use correctly (created class can not be find by dataType), then it will create lots of classes (saved in _cached_cls), never released.

Also, all same DataType have same hash code, there will be many object in a dict with the same hash code, end with hash attach, it's very slow to access this dict (depends on the implementation of CPython).

This PR also improve the performance of inferSchema (avoid the unnecessary converter of object).

cc pwendell  JoshRosen

Author: Davies Liu <davies@databricks.com>

Closes #4808 from davies/leak and squashes the following commits:

6a322a4 [Davies Liu] tests refactor
3da44fc [Davies Liu] fix __eq__ of Singleton
534ac90 [Davies Liu] add more checks
46999dc [Davies Liu] fix tests
d9ae973 [Davies Liu] fix memory leak in sql

python/pyspark/sql/context.py

@@ -17,15 +17,14 @@
 
 import warnings
 import json
-from array import array
 from itertools import imap
 
 from py4j.protocol import Py4JError
 from py4j.java_collections import MapConverter
 
 from pyspark.rdd import RDD, _prepare_for_python_RDD
 from pyspark.serializers import AutoBatchedSerializer, PickleSerializer
-from pyspark.sql.types import StringType, StructType, _verify_type, \
+from pyspark.sql.types import Row, StringType, StructType, _verify_type, \
     _infer_schema, _has_nulltype, _merge_type, _create_converter, _python_to_sql_converter
 from pyspark.sql.dataframe import DataFrame
 
@@ -620,93 +619,6 @@ def _get_hive_ctx(self):
         return self._jvm.HiveContext(self._jsc.sc())
 
 
-def _create_row(fields, values):
-    row = Row(*values)
-    row.__FIELDS__ = fields
-    return row
-
-
-class Row(tuple):
-
-    """
-    A row in L{DataFrame}. The fields in it can be accessed like attributes.
-
-    Row can be used to create a row object by using named arguments,
-    the fields will be sorted by names.
-
-    >>> row = Row(name="Alice", age=11)
-    >>> row
-    Row(age=11, name='Alice')
-    >>> row.name, row.age
-    ('Alice', 11)
-
-    Row also can be used to create another Row like class, then it
-    could be used to create Row objects, such as
-
-    >>> Person = Row("name", "age")
-    >>> Person
-    <Row(name, age)>
-    >>> Person("Alice", 11)
-    Row(name='Alice', age=11)
-    """
-
-    def __new__(self, *args, **kwargs):
-        if args and kwargs:
-            raise ValueError("Can not use both args "
-                             "and kwargs to create Row")
-        if args:
-            # create row class or objects
-            return tuple.__new__(self, args)
-
-        elif kwargs:
-            # create row objects
-            names = sorted(kwargs.keys())
-            values = tuple(kwargs[n] for n in names)
-            row = tuple.__new__(self, values)
-            row.__FIELDS__ = names
-            return row
-
-        else:
-            raise ValueError("No args or kwargs")
-
-    def asDict(self):
-        """
-        Return as an dict
-        """
-        if not hasattr(self, "__FIELDS__"):
-            raise TypeError("Cannot convert a Row class into dict")
-        return dict(zip(self.__FIELDS__, self))
-
-    # let obect acs like class
-    def __call__(self, *args):
-        """create new Row object"""
-        return _create_row(self, args)
-
-    def __getattr__(self, item):
-        if item.startswith("__"):
-            raise AttributeError(item)
-        try:
-            # it will be slow when it has many fields,
-            # but this will not be used in normal cases
-            idx = self.__FIELDS__.index(item)
-            return self[idx]
-        except IndexError:
-            raise AttributeError(item)
-
-    def __reduce__(self):
-        if hasattr(self, "__FIELDS__"):
-            return (_create_row, (self.__FIELDS__, tuple(self)))
-        else:
-            return tuple.__reduce__(self)
-
-    def __repr__(self):
-        if hasattr(self, "__FIELDS__"):
-            return "Row(%s)" % ", ".join("%s=%r" % (k, v)
-                                         for k, v in zip(self.__FIELDS__, self))
-        else:
-            return "<Row(%s)>" % ", ".join(self)
-
-
 def _test():
     import doctest
     from pyspark.context import SparkContext

python/pyspark/sql/dataframe.py

@@ -1025,10 +1025,12 @@ def cast(self, dataType):
             ssql_ctx = sc._jvm.SQLContext(sc._jsc.sc())
             jdt = ssql_ctx.parseDataType(dataType.json())
             jc = self._jc.cast(jdt)
+        else:
+            raise TypeError("unexpected type: %s" % type(dataType))
         return Column(jc)
 
     def __repr__(self):
-        return 'Column<%s>' % self._jdf.toString().encode('utf8')
+        return 'Column<%s>' % self._jc.toString().encode('utf8')
 
 
 def _test():

python/pyspark/sql/tests.py

@@ -24,6 +24,7 @@
 import pydoc
 import shutil
 import tempfile
+import pickle
 
 import py4j
 
@@ -88,6 +89,14 @@ def __eq__(self, other):
             other.x == self.x and other.y == self.y
 
 
+class DataTypeTests(unittest.TestCase):
+    # regression test for SPARK-6055
+    def test_data_type_eq(self):
+        lt = LongType()
+        lt2 = pickle.loads(pickle.dumps(LongType()))
+        self.assertEquals(lt, lt2)
+
+
 class SQLTests(ReusedPySparkTestCase):
 
     @classmethod