The jira for the issue can be found at: https://issues.apache.org/jira/browse/SPARK-2061
Most of spark has used over to consistently using `partitions` instead of `splits`. We should do likewise and add a `partitions` method to JavaRDDLike and have `splits` just call that. We should also go through all cases where other API's (e.g. Python) call `splits` and we should change those to use the newer API.
Author: Anant <anant.asty@gmail.com>
Closes#1062 from anantasty/SPARK-2061 and squashes the following commits:
b83ce6b [Anant] Fixed syntax issue
21f9210 [Anant] Fixed version number in deprecation string
9315b76 [Anant] made related changes to use partitions in python api
8c62dd1 [Anant] Made splits deprecated in JavaRDDLike
So I finally resurrected this PR. It seems the old one against the incubator mirror is no longer available, so I cannot reference it.
This adds initial support for reading Hadoop ```SequenceFile```s, as well as arbitrary Hadoop ```InputFormat```s, in PySpark.
# Overview
The basics are as follows:
1. ```PythonRDD``` object contains the relevant methods, that are in turn invoked by ```SparkContext``` in PySpark
2. The SequenceFile or InputFormat is read on the Scala side and converted from ```Writable``` instances to the relevant Scala classes (in the case of primitives)
3. Pyrolite is used to serialize Java objects. If this fails, the fallback is ```toString```
4. ```PickleSerializer``` on the Python side deserializes.
This works "out the box" for simple ```Writable```s:
* ```Text```
* ```IntWritable```, ```DoubleWritable```, ```FloatWritable```
* ```NullWritable```
* ```BooleanWritable```
* ```BytesWritable```
* ```MapWritable```
It also works for simple, "struct-like" classes. Due to the way Pyrolite works, this requires that the classes satisfy the JavaBeans convenstions (i.e. with fields and a no-arg constructor and getters/setters). (Perhaps in future some sugar for case classes and reflection could be added).
I've tested it out with ```ESInputFormat``` as an example and it works very nicely:
```python
conf = {"es.resource" : "index/type" }
rdd = sc.newAPIHadoopRDD("org.elasticsearch.hadoop.mr.EsInputFormat", "org.apache.hadoop.io.NullWritable", "org.elasticsearch.hadoop.mr.LinkedMapWritable", conf=conf)
rdd.first()
```
I suspect for things like HBase/Cassandra it will be a bit trickier to get it to work out the box.
# Some things still outstanding:
1. ~~Requires ```msgpack-python``` and will fail without it. As originally discussed with Josh, add a ```as_strings``` argument that defaults to ```False```, that can be used if ```msgpack-python``` is not available~~
2. ~~I see from https://github.com/apache/spark/pull/363 that Pyrolite is being used there for SerDe between Scala and Python. @ahirreddy @mateiz what is the plan behind this - is Pyrolite preferred? It seems from a cursory glance that adapting the ```msgpack```-based SerDe here to use Pyrolite wouldn't be too hard~~
3. ~~Support the key and value "wrapper" that would allow a Scala/Java function to be plugged in that would transform whatever the key/value Writable class is into something that can be serialized (e.g. convert some custom Writable to a JavaBean or ```java.util.Map``` that can be easily serialized)~~
4. Support ```saveAsSequenceFile``` and ```saveAsHadoopFile``` etc. This would require SerDe in the reverse direction, that can be handled by Pyrolite. Will work on this as a separate PR
Author: Nick Pentreath <nick.pentreath@gmail.com>
Closes#455 from MLnick/pyspark-inputformats and squashes the following commits:
268df7e [Nick Pentreath] Documentation changes mer @pwendell comments
761269b [Nick Pentreath] Address @pwendell comments, simplify default writable conversions and remove registry.
4c972d8 [Nick Pentreath] Add license headers
d150431 [Nick Pentreath] Merge remote-tracking branch 'upstream/master' into pyspark-inputformats
cde6af9 [Nick Pentreath] Parameterize converter trait
5ebacfa [Nick Pentreath] Update docs for PySpark input formats
a985492 [Nick Pentreath] Move Converter examples to own package
365d0be [Nick Pentreath] Make classes private[python]. Add docs and @Experimental annotation to Converter interface.
eeb8205 [Nick Pentreath] Fix path relative to SPARK_HOME in tests
1eaa08b [Nick Pentreath] HBase -> Cassandra app name oversight
3f90c3e [Nick Pentreath] Merge remote-tracking branch 'upstream/master' into pyspark-inputformats
2c18513 [Nick Pentreath] Add examples for reading HBase and Cassandra InputFormats from Python
b65606f [Nick Pentreath] Add converter interface
5757f6e [Nick Pentreath] Default key/value classes for sequenceFile asre None
085b55f [Nick Pentreath] Move input format tests to tests.py and clean up docs
43eb728 [Nick Pentreath] PySpark InputFormats docs into programming guide
94beedc [Nick Pentreath] Clean up args in PythonRDD. Set key/value converter defaults to None for PySpark context.py methods
1a4a1d6 [Nick Pentreath] Address @mateiz style comments
01e0813 [Nick Pentreath] Merge remote-tracking branch 'upstream/master' into pyspark-inputformats
15a7d07 [Nick Pentreath] Remove default args for key/value classes. Arg names to camelCase
9fe6bd5 [Nick Pentreath] Merge remote-tracking branch 'upstream/master' into pyspark-inputformats
84fe8e3 [Nick Pentreath] Python programming guide space formatting
d0f52b6 [Nick Pentreath] Python programming guide
7caa73a [Nick Pentreath] Merge remote-tracking branch 'upstream/master' into pyspark-inputformats
93ef995 [Nick Pentreath] Add back context.py changes
9ef1896 [Nick Pentreath] Recover earlier changes lost in previous merge for serializers.py
077ecb2 [Nick Pentreath] Recover earlier changes lost in previous merge for context.py
5af4770 [Nick Pentreath] Merge branch 'master' into pyspark-inputformats
35b8e3a [Nick Pentreath] Another fix for test ordering
bef3afb [Nick Pentreath] Merge remote-tracking branch 'upstream/master' into pyspark-inputformats
e001b94 [Nick Pentreath] Fix test failures due to ordering
78978d9 [Nick Pentreath] Add doc for SequenceFile and InputFormat support to Python programming guide
64eb051 [Nick Pentreath] Scalastyle fix
e7552fa [Nick Pentreath] Merge branch 'master' into pyspark-inputformats
44f2857 [Nick Pentreath] Remove msgpack dependency and switch serialization to Pyrolite, plus some clean up and refactoring
c0ebfb6 [Nick Pentreath] Change sequencefile test data generator to easily be called from PySpark tests
1d7c17c [Nick Pentreath] Amend tests to auto-generate sequencefile data in temp dir
17a656b [Nick Pentreath] remove binary sequencefile for tests
f60959e [Nick Pentreath] Remove msgpack dependency and serializer from PySpark
450e0a2 [Nick Pentreath] Merge branch 'master' into pyspark-inputformats
31a2fff [Nick Pentreath] Scalastyle fixes
fc5099e [Nick Pentreath] Add Apache license headers
4e08983 [Nick Pentreath] Clean up docs for PySpark context methods
b20ec7e [Nick Pentreath] Clean up merge duplicate dependencies
951c117 [Nick Pentreath] Merge branch 'master' into pyspark-inputformats
f6aac55 [Nick Pentreath] Bring back msgpack
9d2256e [Nick Pentreath] Merge branch 'master' into pyspark-inputformats
1bbbfb0 [Nick Pentreath] Clean up SparkBuild from merge
a67dfad [Nick Pentreath] Clean up Msgpack serialization and registering
7237263 [Nick Pentreath] Add back msgpack serializer and hadoop file code lost during merging
25da1ca [Nick Pentreath] Add generator for nulls, bools, bytes and maps
65360d5 [Nick Pentreath] Adding test SequenceFiles
0c612e5 [Nick Pentreath] Merge branch 'master' into pyspark-inputformats
d72bf18 [Nick Pentreath] msgpack
dd57922 [Nick Pentreath] Merge remote-tracking branch 'upstream/master' into pyspark-inputformats
e67212a [Nick Pentreath] Add back msgpack dependency
f2d76a0 [Nick Pentreath] Merge branch 'master' into pyspark-inputformats
41856a5 [Nick Pentreath] Merge branch 'master' into pyspark-inputformats
97ef708 [Nick Pentreath] Remove old writeToStream
2beeedb [Nick Pentreath] Merge remote-tracking branch 'upstream/master' into pyspark-inputformats
795a763 [Nick Pentreath] Change name to WriteInputFormatTestDataGenerator. Cleanup some var names. Use SPARK_HOME in path for writing test sequencefile data.
174f520 [Nick Pentreath] Add back graphx settings
703ee65 [Nick Pentreath] Add back msgpack
619c0fa [Nick Pentreath] Merge remote-tracking branch 'upstream/master' into pyspark-inputformats
1c8efbc [Nick Pentreath] Merge remote-tracking branch 'upstream/master' into pyspark-inputformats
eb40036 [Nick Pentreath] Remove unused comment lines
4d7ef2e [Nick Pentreath] Fix indentation
f1d73e3 [Nick Pentreath] mergeConfs returns a copy rather than mutating one of the input arguments
0f5cd84 [Nick Pentreath] Remove unused pair UTF8 class. Add comments to msgpack deserializer
4294cbb [Nick Pentreath] Add old Hadoop api methods. Clean up and expand comments. Clean up argument names
818a1e6 [Nick Pentreath] Add seqencefile and Hadoop InputFormat support to PythonRDD
4e7c9e3 [Nick Pentreath] Merge remote-tracking branch 'upstream/master' into pyspark-inputformats
c304cc8 [Nick Pentreath] Adding supporting sequncefiles for tests. Cleaning up
4b0a43f [Nick Pentreath] Refactoring utils into own objects. Cleaning up old commented-out code
d86325f [Nick Pentreath] Initial WIP of PySpark support for SequenceFile and arbitrary Hadoop InputFormat
Author: Kan Zhang <kzhang@apache.org>
Closes#755 from kanzhang/SPARK-1161 and squashes the following commits:
24ed8a2 [Kan Zhang] [SPARK-1161] Fixing doc tests
44e0615 [Kan Zhang] [SPARK-1161] Adding an optional batchSize with default value 10
d929429 [Kan Zhang] [SPARK-1161] Add saveAsObjectFile and SparkContext.objectFile in Python
This patch simply ports over the Scala implementation of RDD#take(), which reads the first partition at the driver, then decides how many more partitions it needs to read and will possibly start a real job if it's more than 1. (Note that SparkContext#runJob(allowLocal=true) only runs the job locally if there's 1 partition selected and no parent stages.)
Author: Aaron Davidson <aaron@databricks.com>
Closes#922 from aarondav/take and squashes the following commits:
fa06df9 [Aaron Davidson] SPARK-1839: PySpark RDD#take() shouldn't always read from driver
Added doctest for method textFile and description for methods _initialize_context and _ensure_initialized in context.py
Author: Jyotiska NK <jyotiska123@gmail.com>
Closes#187 from jyotiska/pyspark_context and squashes the following commits:
356f945 [Jyotiska NK] Added doctest for textFile method in context.py
5b23686 [Jyotiska NK] Updated context.py with method descriptions
If I run the following on a YARN cluster
```
bin/spark-submit sheep.py --master yarn-client
```
it fails because of a mismatch in paths: `spark-submit` thinks that `sheep.py` resides on HDFS, and balks when it can't find the file there. A natural workaround is to add the `file:` prefix to the file:
```
bin/spark-submit file:/path/to/sheep.py --master yarn-client
```
However, this also fails. This time it is because python does not understand URI schemes.
This PR fixes this by automatically resolving all paths passed as command line argument to `spark-submit` properly. This has the added benefit of keeping file and jar paths consistent across different cluster modes. For python, we strip the URI scheme before we actually try to run it.
Much of the code is originally written by @mengxr. Tested on YARN cluster. More tests pending.
Author: Andrew Or <andrewor14@gmail.com>
Closes#853 from andrewor14/submit-paths and squashes the following commits:
0bb097a [Andrew Or] Format path correctly before adding it to PYTHONPATH
323b45c [Andrew Or] Include --py-files on PYTHONPATH for pyspark shell
3c36587 [Andrew Or] Improve error messages (minor)
854aa6a [Andrew Or] Guard against NPE if user gives pathological paths
6638a6b [Andrew Or] Fix spark-shell jar paths after #849 went in
3bb0359 [Andrew Or] Update more comments (minor)
2a1f8a0 [Andrew Or] Update comments (minor)
6af2c77 [Andrew Or] Merge branch 'master' of github.com:apache/spark into submit-paths
a68c4d1 [Andrew Or] Handle Windows python file path correctly
427a250 [Andrew Or] Resolve paths properly for Windows
a591a4a [Andrew Or] Update tests for resolving URIs
6c8621c [Andrew Or] Move resolveURIs to Utils
db8255e [Andrew Or] Merge branch 'master' of github.com:apache/spark into submit-paths
f542dce [Andrew Or] Fix outdated tests
691c4ce [Andrew Or] Ignore special primary resource names
5342ac7 [Andrew Or] Add missing space in error message
02f77f3 [Andrew Or] Resolve command line arguments to spark-submit properly
Author: Kan Zhang <kzhang@apache.org>
Closes#697 from kanzhang/SPARK-1519 and squashes the following commits:
4f8d1ed [Kan Zhang] [SPARK-1519] Support minPartitions param of wholeTextFiles() in PySpark
This patch includes several cleanups to PythonRDD, focused around fixing [SPARK-1579](https://issues.apache.org/jira/browse/SPARK-1579) cleanly. Listed in order of approximate importance:
- The Python daemon waits for Spark to close the socket before exiting,
in order to avoid causing spurious IOExceptions in Spark's
`PythonRDD::WriterThread`.
- Removes the Python Monitor Thread, which polled for task cancellations
in order to kill the Python worker. Instead, we do this in the
onCompleteCallback, since this is guaranteed to be called during
cancellation.
- Adds a "completed" variable to TaskContext to avoid the issue noted in
[SPARK-1019](https://issues.apache.org/jira/browse/SPARK-1019), where onCompleteCallbacks may be execution-order dependent.
Along with this, I removed the "context.interrupted = true" flag in
the onCompleteCallback.
- Extracts PythonRDD::WriterThread to its own class.
Since this patch provides an alternative solution to [SPARK-1019](https://issues.apache.org/jira/browse/SPARK-1019), I did test it with
```
sc.textFile("latlon.tsv").take(5)
```
many times without error.
Additionally, in order to test the unswallowed exceptions, I performed
```
sc.textFile("s3n://<big file>").count()
```
and cut my internet during execution. Prior to this patch, we got the "stdin writer exited early" message, which was unhelpful. Now, we get the SocketExceptions propagated through Spark to the user and get proper (though unsuccessful) task retries.
Author: Aaron Davidson <aaron@databricks.com>
Closes#640 from aarondav/pyspark-io and squashes the following commits:
b391ff8 [Aaron Davidson] Detect "clean socket shutdowns" and stop waiting on the socket
c0c49da [Aaron Davidson] SPARK-1579: Clean up PythonRDD and avoid swallowing IOExceptions
This PR updates spark-submit to allow submitting Python scripts (currently only with deploy-mode=client, but that's all that was supported before) and updates the PySpark code to properly find various paths, etc. One significant change is that we assume we can always find the Python files either from the Spark assembly JAR (which will happen with the Maven assembly build in make-distribution.sh) or from SPARK_HOME (which will exist in local mode even if you use sbt assembly, and should be enough for testing). This means we no longer need a weird hack to modify the environment for YARN.
This patch also updates the Python worker manager to run python with -u, which means unbuffered output (send it to our logs right away instead of waiting a while after stuff was written); this should simplify debugging.
In addition, it fixes https://issues.apache.org/jira/browse/SPARK-1709, setting the main class from a JAR's Main-Class attribute if not specified by the user, and fixes a few help strings and style issues in spark-submit.
In the future we may want to make the `pyspark` shell use spark-submit as well, but it seems unnecessary for 1.0.
Author: Matei Zaharia <matei@databricks.com>
Closes#664 from mateiz/py-submit and squashes the following commits:
15e9669 [Matei Zaharia] Fix some uses of path.separator property
051278c [Matei Zaharia] Small style fixes
0afe886 [Matei Zaharia] Add license headers
4650412 [Matei Zaharia] Add pyFiles to PYTHONPATH in executors, remove old YARN stuff, add tests
15f8e1e [Matei Zaharia] Set PYTHONPATH in PythonWorkerFactory in case it wasn't set from outside
47c0655 [Matei Zaharia] More work to make spark-submit work with Python:
d4375bd [Matei Zaharia] Clean up description of spark-submit args a bit and add Python ones
* Additions to the PySpark API to cancel jobs
* Monitor Thread in PythonRDD to kill Python workers if a task is interrupted
Author: Ahir Reddy <ahirreddy@gmail.com>
Closes#541 from ahirreddy/python-cancel and squashes the following commits:
dfdf447 [Ahir Reddy] Changed success -> completed and made logging message clearer
6c860ab [Ahir Reddy] PR Comments
4b4100a [Ahir Reddy] Success flag
adba6ed [Ahir Reddy] Destroy python workers
27a2f8f [Ahir Reddy] Start the writer thread...
d422f7b [Ahir Reddy] Remove unnecesssary vals
adda337 [Ahir Reddy] Busy wait on the ocntext.interrupted flag, and then kill the python worker
d9e472f [Ahir Reddy] Revert "removed unnecessary vals"
5b9cae5 [Ahir Reddy] removed unnecessary vals
07b54d9 [Ahir Reddy] Fix canceling unit test
8ae9681 [Ahir Reddy] Don't interrupt worker
7722342 [Ahir Reddy] Monitor Thread for python workers
db04e16 [Ahir Reddy] Added canceling api to PySpark
https://issues.apache.org/jira/browse/SPARK-1483
From the original JIRA: " The parameter name is part of the public API in Scala and Python, since you can pass named parameters to a method, so we should name it to this more descriptive term. Everywhere else we refer to "splits" as partitions." - @mateiz
Author: CodingCat <zhunansjtu@gmail.com>
Closes#430 from CodingCat/SPARK-1483 and squashes the following commits:
4b60541 [CodingCat] deprecate defaultMinSplits
ba2c663 [CodingCat] Rename minSplits to minPartitions in public APIs
Move the PR#468 of apache-incubator-spark to the apache-spark
"Adding an option to persist Spark RDD blocks into Tachyon."
Author: Haoyuan Li <haoyuan@cs.berkeley.edu>
Author: RongGu <gurongwalker@gmail.com>
Closes#158 from RongGu/master and squashes the following commits:
72b7768 [Haoyuan Li] merge master
9f7fa1b [Haoyuan Li] fix code style
ae7834b [Haoyuan Li] minor cleanup
a8b3ec6 [Haoyuan Li] merge master branch
e0f4891 [Haoyuan Li] better check offheap.
55b5918 [RongGu] address matei's comment on the replication of offHeap storagelevel
7cd4600 [RongGu] remove some logic code for tachyonstore's replication
51149e7 [RongGu] address aaron's comment on returning value of the remove() function in tachyonstore
8adfcfa [RongGu] address arron's comment on inTachyonSize
120e48a [RongGu] changed the root-level dir name in Tachyon
5cc041c [Haoyuan Li] address aaron's comments
9b97935 [Haoyuan Li] address aaron's comments
d9a6438 [Haoyuan Li] fix for pspark
77d2703 [Haoyuan Li] change python api.git status
3dcace4 [Haoyuan Li] address matei's comments
91fa09d [Haoyuan Li] address patrick's comments
589eafe [Haoyuan Li] use TRY_CACHE instead of MUST_CACHE
64348b2 [Haoyuan Li] update conf docs.
ed73e19 [Haoyuan Li] Merge branch 'master' of github.com:RongGu/spark-1
619a9a8 [RongGu] set number of directories in TachyonStore back to 64; added a TODO tag for duplicated code from the DiskStore
be79d77 [RongGu] find a way to clean up some unnecessay metods and classed to make the code simpler
49cc724 [Haoyuan Li] update docs with off_headp option
4572f9f [RongGu] reserving the old apply function API of StorageLevel
04301d3 [RongGu] rename StorageLevel.TACHYON to Storage.OFF_HEAP
c9aeabf [RongGu] rename the StorgeLevel.TACHYON as StorageLevel.OFF_HEAP
76805aa [RongGu] unifies the config properties name prefix; add the configs into docs/configuration.md
e700d9c [RongGu] add the SparkTachyonHdfsLR example and some comments
fd84156 [RongGu] use randomUUID to generate sparkapp directory name on tachyon;minor code style fix
939e467 [Haoyuan Li] 0.4.1-thrift from maven central
86a2eab [Haoyuan Li] tachyon 0.4.1-thrift is in the staging repo. but jenkins failed to download it. temporarily revert it back to 0.4.1
16c5798 [RongGu] make the dependency on tachyon as tachyon-0.4.1-thrift
eacb2e8 [RongGu] Merge branch 'master' of https://github.com/RongGu/spark-1
bbeb4de [RongGu] fix the JsonProtocolSuite test failure problem
6adb58f [RongGu] Merge branch 'master' of https://github.com/RongGu/spark-1
d827250 [RongGu] fix JsonProtocolSuie test failure
716e93b [Haoyuan Li] revert the version
ca14469 [Haoyuan Li] bump tachyon version to 0.4.1-thrift
2825a13 [RongGu] up-merging to the current master branch of the apache spark
6a22c1a [Haoyuan Li] fix scalastyle
8968b67 [Haoyuan Li] exclude more libraries from tachyon dependency to be the same as referencing tachyon-client.
77be7e8 [RongGu] address mateiz's comment about the temp folder name problem. The implementation followed mateiz's advice.
1dcadf9 [Haoyuan Li] typo
bf278fa [Haoyuan Li] fix python tests
e82909c [Haoyuan Li] minor cleanup
776a56c [Haoyuan Li] address patrick's and ali's comments from the previous PR
8859371 [Haoyuan Li] various minor fixes and clean up
e3ddbba [Haoyuan Li] add doc to use Tachyon cache mode.
fcaeab2 [Haoyuan Li] address Aaron's comment
e554b1e [Haoyuan Li] add python code
47304b3 [Haoyuan Li] make tachyonStore in BlockMananger lazy val; add more comments StorageLevels.
dc8ef24 [Haoyuan Li] add old storelevel constructor
e01a271 [Haoyuan Li] update tachyon 0.4.1
8011a96 [RongGu] fix a brought-in mistake in StorageLevel
70ca182 [RongGu] a bit change in comment
556978b [RongGu] fix the scalastyle errors
791189b [RongGu] "Adding an option to persist Spark RDD blocks into Tachyon." move the PR#468 of apache-incubator-spark to the apache-spark
Also clarified comment on each file having to fit in memory
Author: Matei Zaharia <matei@databricks.com>
Closes#327 from mateiz/py-whole-files and squashes the following commits:
9ad64a5 [Matei Zaharia] SPARK-1414. Python API for SparkContext.wholeTextFiles
Author: jyotiska <jyotiska123@gmail.com>
Closes#34 from jyotiska/pyspark_code and squashes the following commits:
c9439be [jyotiska] replaced dict with namedtuple
a6bf4cd [jyotiska] added callsite info for context.py
The following Python APIs are added,
RDD.id()
SparkContext.setJobGroup()
SparkContext.setLocalProperty()
SparkContext.getLocalProperty()
SparkContext.sparkUser()
was raised earlier as a part of apache/incubator-spark#486
Author: Prabin Banka <prabin.banka@imaginea.com>
Closes#75 from prabinb/python-api-backup and squashes the following commits:
cc3c6cd [Prabin Banka] Added missing Python APIs
Patch to allow PySpark to use existing JVM and Gateway. Changes to PySpark implementation of SparkConf to take existing SparkConf JVM handle. Change to PySpark SparkContext to allow subclass specific context initialization.
Author: Ahir Reddy <ahirreddy@gmail.com>
Closes#622 from ahirreddy/pyspark-existing-jvm and squashes the following commits:
a86f457 [Ahir Reddy] Patch to allow PySpark to use existing JVM and Gateway. Changes to PySpark implementation of SparkConf to take existing SparkConf JVM handle. Change to PySpark SparkContext to allow subclass specific context initialization.
This fixes SPARK-1043, a bug introduced in 0.9.0
where PySpark couldn't serialize strings > 64kB.
This fix was written by @tyro89 and @bouk in #512.
This commit squashes and rebases their pull request
in order to fix some merge conflicts.
The test in context.py created two different instances of the
SparkContext class by copying "globals", so that some tests can have a
global "sc" object and others can try initializing their own contexts.
This led to two JVM gateways being created since SparkConf also looked
at pyspark.context.SparkContext to get the JVM.
For now, this only adds MarshalSerializer, but it lays the groundwork
for other supporting custom serializers. Many of these mechanisms
can also be used to support deserialization of different data formats
sent by Java, such as data encoded by MsgPack.
This also fixes a bug in SparkContext.union().
If we support custom serializers, the Python
worker will know what type of input to expect,
so we won't need to wrap Tuple2 and Strings into
pickled tuples and strings.
The constructor for SparkContext should pass in self so that we track
the current context and produce errors if another one is created. Add
a doctest to make sure creating multiple contexts triggers the
exception.
Add a new classmethod to SparkContext to set system properties like is
possible in Scala/Java. Unlike the Java/Scala implementations, there's
no access to System until the JVM bridge is created. Since
SparkContext handles that, move the initialization of the JVM
connection to a separate classmethod that can safely be called
repeatedly as long as the same instance (or no instance) is provided.
The sc.StorageLevel -> StorageLevel pathway is a bit janky, but otherwise
the shell would have to call a private method of SparkContext. Having
StorageLevel available in sc also doesn't seem like the end of the world.
There may be a better solution, though.
As for creating the StorageLevel object itself, this seems to be the best
way in Python 2 for creating singleton, enum-like objects:
http://stackoverflow.com/questions/36932/how-can-i-represent-an-enum-in-python
One unfortunate consequence of this fix is that we materialize any
collections that are given to us as generators, but this seems necessary
to get reasonable behavior on small collections. We could add a
batchSize parameter later to bypass auto-computation of batch size if
this becomes a problem (e.g. if users really want to parallelize big
generators nicely)
The problem was that the gateway was being initialized whenever the
pyspark.context module was loaded. The fix uses lazy initialization
that occurs only when SparkContext instances are actually constructed.
I also made the gateway and jvm variables private.
This change results in ~3-4x performance improvement when running the
PySpark unit tests.
