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[SPARK-4488][PySpark] Add control over map-side aggregation #3366

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[SPARK-4488][PySpark] Add control over map-side aggregation #3366

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a4a5804
add control over map-side aggregation
uncleGen Nov 19, 2014
e3b0bc4
fix
uncleGen Nov 19, 2014
66561d4
fix
uncleGen Nov 19, 2014
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33 changes: 18 additions & 15 deletions python/pyspark/rdd.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1319,7 +1319,7 @@ def values(self):
"""
return self.map(lambda (k, v): v)

def reduceByKey(self, func, numPartitions=None):
def reduceByKey(self, func, numPartitions=None, mapSideCombine=True):
"""
Merge the values for each key using an associative reduce function.

Expand All @@ -1334,7 +1334,7 @@ def reduceByKey(self, func, numPartitions=None):
>>> sorted(rdd.reduceByKey(add).collect())
[('a', 2), ('b', 1)]
"""
return self.combineByKey(lambda x: x, func, func, numPartitions)
return self.combineByKey(lambda x: x, func, func, numPartitions, mapSideCombine)

def reduceByKeyLocally(self, func):
"""
Expand Down Expand Up @@ -1516,9 +1516,8 @@ def add_shuffle_key(split, iterator):
rdd._partitionFunc = partitionFunc
return rdd

# TODO: add control over map-side aggregation
def combineByKey(self, createCombiner, mergeValue, mergeCombiners,
numPartitions=None):
numPartitions=None, mapSideCombine=True):
"""
Generic function to combine the elements for each key using a custom
set of aggregation functions.
Expand Down Expand Up @@ -1559,18 +1558,21 @@ def combineLocally(iterator):
merger.mergeValues(iterator)
return merger.iteritems()

locally_combined = self.mapPartitions(combineLocally)
shuffled = locally_combined.partitionBy(numPartitions)

def _mergeCombiners(iterator):
merger = ExternalMerger(agg, memory, serializer) \
if spill else InMemoryMerger(agg)
merger.mergeCombiners(iterator)
return merger.iteritems()

return shuffled.mapPartitions(_mergeCombiners, True)
if mapSideCombine:
locally_combined = self.mapPartitions(combineLocally)
shuffled = locally_combined.partitionBy(numPartitions)
return shuffled.mapPartitions(_mergeCombiners)
else:
shuffled = self.partitionBy(numPartitions)
return shuffled.mapPartitions(combineLocally)

def aggregateByKey(self, zeroValue, seqFunc, combFunc, numPartitions=None):
def aggregateByKey(self, zeroValue, seqFunc, combFunc, numPartitions=None, mapSideCombine=True):
"""
Aggregate the values of each key, using given combine functions and a neutral
"zero value". This function can return a different result type, U, than the type
Expand All @@ -1584,9 +1586,9 @@ def createZero():
return copy.deepcopy(zeroValue)

return self.combineByKey(
lambda v: seqFunc(createZero(), v), seqFunc, combFunc, numPartitions)
lambda v: seqFunc(createZero(), v), seqFunc, combFunc, numPartitions, mapSideCombine)

def foldByKey(self, zeroValue, func, numPartitions=None):
def foldByKey(self, zeroValue, func, numPartitions=None, mapSideCombine=True):
"""
Merge the values for each key using an associative function "func"
and a neutral "zeroValue" which may be added to the result an
Expand All @@ -1601,10 +1603,11 @@ def foldByKey(self, zeroValue, func, numPartitions=None):
def createZero():
return copy.deepcopy(zeroValue)

return self.combineByKey(lambda v: func(createZero(), v), func, func, numPartitions)
return self.combineByKey(
lambda v: func(createZero(), v), func, func, numPartitions, mapSideCombine)

# TODO: support variant with custom partitioner
def groupByKey(self, numPartitions=None):
def groupByKey(self, numPartitions=None, mapSideCombine=True):
"""
Group the values for each key in the RDD into a single sequence.
Hash-partitions the resulting RDD with into numPartitions partitions.
Expand All @@ -1629,8 +1632,8 @@ def mergeCombiners(a, b):
a.extend(b)
return a

return self.combineByKey(createCombiner, mergeValue, mergeCombiners,
numPartitions).mapValues(lambda x: ResultIterable(x))
return self.combineByKey(createCombiner, mergeValue, mergeCombiners, numPartitions,
mapSideCombine).mapValues(lambda x: ResultIterable(x))

def flatMapValues(self, f):
"""
Expand Down