160 lines
6.1 KiB
Python
160 lines
6.1 KiB
Python
import os
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import atexit
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from tempfile import NamedTemporaryFile
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from pyspark.broadcast import Broadcast
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from pyspark.java_gateway import launch_gateway
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from pyspark.serializers import dump_pickle, write_with_length, batched
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from pyspark.rdd import RDD
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from py4j.java_collections import ListConverter
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class SparkContext(object):
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"""
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Main entry point for Spark functionality. A SparkContext represents the
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connection to a Spark cluster, and can be used to create L{RDD}s and
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broadcast variables on that cluster.
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"""
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gateway = launch_gateway()
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jvm = gateway.jvm
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_readRDDFromPickleFile = jvm.PythonRDD.readRDDFromPickleFile
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_writeIteratorToPickleFile = jvm.PythonRDD.writeIteratorToPickleFile
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_takePartition = jvm.PythonRDD.takePartition
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def __init__(self, master, jobName, sparkHome=None, pyFiles=None,
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environment=None, batchSize=1024):
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"""
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Create a new SparkContext.
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@param master: Cluster URL to connect to
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(e.g. mesos://host:port, spark://host:port, local[4]).
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@param jobName: A name for your job, to display on the cluster web UI
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@param sparkHome: Location where Spark is installed on cluster nodes.
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@param pyFiles: Collection of .zip or .py files to send to the cluster
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and add to PYTHONPATH. These can be paths on the local file
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system or HDFS, HTTP, HTTPS, or FTP URLs.
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@param environment: A dictionary of environment variables to set on
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worker nodes.
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@param batchSize: The number of Python objects represented as a single
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Java object. Set 1 to disable batching or -1 to use an
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unlimited batch size.
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"""
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self.master = master
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self.jobName = jobName
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self.sparkHome = sparkHome or None # None becomes null in Py4J
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self.environment = environment or {}
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self.batchSize = batchSize # -1 represents a unlimited batch size
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# Create the Java SparkContext through Py4J
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empty_string_array = self.gateway.new_array(self.jvm.String, 0)
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self._jsc = self.jvm.JavaSparkContext(master, jobName, sparkHome,
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empty_string_array)
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self.pythonExec = os.environ.get("PYSPARK_PYTHON", 'python')
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# Broadcast's __reduce__ method stores Broadcast instances here.
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# This allows other code to determine which Broadcast instances have
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# been pickled, so it can determine which Java broadcast objects to
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# send.
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self._pickled_broadcast_vars = set()
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# Deploy any code dependencies specified in the constructor
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for path in (pyFiles or []):
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self.addPyFile(path)
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@property
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def defaultParallelism(self):
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"""
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Default level of parallelism to use when not given by user (e.g. for
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reduce tasks)
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"""
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return self._jsc.sc().defaultParallelism()
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def __del__(self):
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if self._jsc:
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self._jsc.stop()
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def stop(self):
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"""
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Shut down the SparkContext.
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"""
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self._jsc.stop()
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self._jsc = None
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def parallelize(self, c, numSlices=None):
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"""
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Distribute a local Python collection to form an RDD.
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"""
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numSlices = numSlices or self.defaultParallelism
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# Calling the Java parallelize() method with an ArrayList is too slow,
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# because it sends O(n) Py4J commands. As an alternative, serialized
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# objects are written to a file and loaded through textFile().
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tempFile = NamedTemporaryFile(delete=False)
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atexit.register(lambda: os.unlink(tempFile.name))
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if self.batchSize != 1:
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c = batched(c, self.batchSize)
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for x in c:
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write_with_length(dump_pickle(x), tempFile)
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tempFile.close()
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jrdd = self._readRDDFromPickleFile(self._jsc, tempFile.name, numSlices)
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return RDD(jrdd, self)
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def textFile(self, name, minSplits=None):
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"""
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Read a text file from HDFS, a local file system (available on all
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nodes), or any Hadoop-supported file system URI, and return it as an
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RDD of Strings.
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"""
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minSplits = minSplits or min(self.defaultParallelism, 2)
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jrdd = self._jsc.textFile(name, minSplits)
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return RDD(jrdd, self)
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def union(self, rdds):
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"""
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Build the union of a list of RDDs.
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"""
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first = rdds[0]._jrdd
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rest = [x._jrdd for x in rdds[1:]]
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rest = ListConverter().convert(rest, self.gateway._gateway_client)
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return RDD(self._jsc.union(first, rest), self)
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def broadcast(self, value):
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"""
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Broadcast a read-only variable to the cluster, returning a C{Broadcast}
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object for reading it in distributed functions. The variable will be
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sent to each cluster only once.
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"""
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jbroadcast = self._jsc.broadcast(bytearray(dump_pickle(value)))
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return Broadcast(jbroadcast.id(), value, jbroadcast,
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self._pickled_broadcast_vars)
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def addFile(self, path):
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"""
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Add a file to be downloaded into the working directory of this Spark
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job on every node. The C{path} passed can be either a local file,
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a file in HDFS (or other Hadoop-supported filesystems), or an HTTP,
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HTTPS or FTP URI.
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"""
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self._jsc.sc().addFile(path)
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def clearFiles(self):
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"""
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Clear the job's list of files added by L{addFile} or L{addPyFile} so
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that they do not get downloaded to any new nodes.
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"""
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# TODO: remove added .py or .zip files from the PYTHONPATH?
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self._jsc.sc().clearFiles()
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def addPyFile(self, path):
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"""
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Add a .py or .zip dependency for all tasks to be executed on this
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SparkContext in the future. The C{path} passed can be either a local
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file, a file in HDFS (or other Hadoop-supported filesystems), or an
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HTTP, HTTPS or FTP URI.
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"""
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self.addFile(path)
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filename = path.split("/")[-1]
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os.environ["PYTHONPATH"] = \
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"%s:%s" % (filename, os.environ["PYTHONPATH"])
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