[Core] Upgrading ScalaStyle version to 0.5 and removing SparkSpaceAfterCommentStartChecker.

Author: prudhvi <prudhvi953@gmail.com>

Closes #2799 from prudhvije/ScalaStyle/space-after-comment-start and squashes the following commits:

fc263a1 [prudhvi] [Core] Using scalastyle to check the space after comment start
[SPARK-3944][Core] Code re-factored as suggested

Author: Shiti <ssaxena.ece@gmail.com>

Closes #2810 from Shiti/master and squashes the following commits:

051d82f [Shiti] setting the default value of uri scheme to "file"  where matching "file" or None yields the same result
[SPARK-3971] [MLLib] [PySpark] hotfix: Customized pickler should work in cluster mode

Customized pickler should be registered before unpickling, but in executor, there is no way to register the picklers before run the tasks.

So, we need to register the picklers in the tasks itself, duplicate the javaToPython() and pythonToJava() in MLlib, call SerDe.initialize() before pickling or unpickling.

Author: Davies Liu <davies.liu@gmail.com>

Closes #2830 from davies/fix_pickle and squashes the following commits:

0c85fb9 [Davies Liu] revert the privacy change
6b94e15 [Davies Liu] use JavaConverters instead of JavaConversions
0f02050 [Davies Liu] hotfix: Customized pickler does not work in cluster
[SQL] Fixes the race condition that may cause test failure

The removed `Future` was used to end the test case as soon as the Spark SQL CLI process exits. When the process exits prematurely, this mechanism prevents the test case to wait until timeout. But it also creates a race condition: when `foundAllExpectedAnswers.tryFailure` is called, there are chances that the last expected output line of the CLI process hasn't been caught by the main logics of the test code, thus fails the test case.

Removing this `Future` doesn't affect correctness.

Author: Cheng Lian <lian.cs.zju@gmail.com>

Closes #2823 from liancheng/clean-clisuite and squashes the following commits:

489a97c [Cheng Lian] Fixes the race condition that may cause test failure
SPARK-3874: Provide stable TaskContext API

This is a small number of clean-up changes on top of #2782. Closes #2782.

Author: Prashant Sharma <prashant.s@imaginea.com>
Author: Patrick Wendell <pwendell@gmail.com>

Closes #2803 from pwendell/pr-2782 and squashes the following commits:

56d5b7a [Patrick Wendell] Minor clean-up
44089ec [Patrick Wendell] Clean-up the TaskContext API.
ed551ce [Prashant Sharma] Fixed a typo
df261d0 [Prashant Sharma] Josh's suggestion
facf3b1 [Prashant Sharma] Fixed the mima issue.
7ecc2fe [Prashant Sharma] CR, Moved implementations to TaskContextImpl
bbd9e05 [Prashant Sharma] adding missed out files to git.
ef633f5 [Prashant Sharma] SPARK-3874, Provide stable TaskContext API
[SPARK-3923] Increase Akka heartbeat pause above heartbeat interval

Something about the 2.3.4 upgrade seems to have made the issue manifest where all the services disconnect from each other after exactly 1000 seconds (which is the heartbeat interval). [This post](https://groups.google.com/forum/#!topic/akka-user/X3xzpTCbEFs) suggests that heartbeat pause should be greater than heartbeat interval, and increasing the pause from 600s to 6000s seems to have rectified the issue. My current cluster has now exceeded 1400s of uptime without failure!

I do not know why this fixed it, because the threshold we have set for the failure detector is the exponent of a timeout, and 300 is extremely large. Perhaps the default failure detector changed in 2.3.4 and now ignores threshold.

Author: Aaron Davidson <aaron@databricks.com>

Closes #2784 from aarondav/fix-timeout and squashes the following commits:

bd1151a [Aaron Davidson] Increase pause, don't decrease interval
9cb0372 [Aaron Davidson] [SPARK-3923] Decrease Akka heartbeat interval below heartbeat pause
[SQL]typo in HiveFromSpark

Author: Kun Li <jacky.likun@gmail.com>

Closes #2809 from jackylk/patch-1 and squashes the following commits:

46c926b [Kun Li] typo in HiveFromSpark
[SPARK-3941][CORE] _remainingmem should not increase twice when updateBlockInfo

In BlockManagermasterActor, _remainingMem would increase memSize for twice when updateBlockInfo if new storageLevel is invalid and old storageLevel is "useMemory". Also, _remainingMem should increase with original memory size instead of new memSize.

Author: Zhang, Liye <liye.zhang@intel.com>

Closes #2792 from liyezhang556520/spark-3941-remainMem and squashes the following commits:

3d487cc [Zhang, Liye] make the code concise
0380a32 [Zhang, Liye] [SPARK-3941][CORE] _remainingmem should not increase twice when updateBlockInfo
[SPARK-3890][Docs]remove redundant spark.executor.memory in doc

Introduced in https://github.com/pwendell/spark/commit/f7e79bc42c1635686c3af01eef147dae92de2529, I'm not sure why we need two spark.executor.memory here.

Author: WangTaoTheTonic <barneystinson@aliyun.com>
Author: WangTao <barneystinson@aliyun.com>

Closes #2745 from WangTaoTheTonic/redundantconfig and squashes the following commits:

e7564dc [WangTao] too long line
fdbdb1f [WangTaoTheTonic] trivial workaround
d06b6e5 [WangTaoTheTonic] remove redundant spark.executor.memory in doc
[SPARK-3741] Add afterExecute for handleConnectExecutor

Sorry. I found that I forgot to add `afterExecute` for `handleConnectExecutor` in #2593.

Author: zsxwing <zsxwing@gmail.com>

Closes #2794 from zsxwing/SPARK-3741 and squashes the following commits:

a0bc4dd [zsxwing] Add afterExecute for handleConnectExecutor
[SPARK-3067] JobProgressPage could not show Fair Scheduler Pools section sometimes

JobProgressPage could not show Fair Scheduler Pools section sometimes.
SparkContext starts webui and then postEnvironmentUpdate. Sometimes JobProgressPage is accessed between webui starting and postEnvironmentUpdate, then the lazy val isFairScheduler will be false. The Fair Scheduler Pools section will not display any more.

Author: yantangzhai <tyz0303@163.com>
Author: YanTangZhai <hakeemzhai@tencent.com>

Closes #1966 from YanTangZhai/SPARK-3067 and squashes the following commits:

d4323f8 [yantangzhai] update [SPARK-3067] JobProgressPage could not show Fair Scheduler Pools section sometimes
8a00106 [YanTangZhai] Merge pull request #6 from apache/master
b6391cc [yantangzhai] revert [SPARK-3067] JobProgressPage could not show Fair Scheduler Pools section sometimes
d2226cd [yantangzhai] [SPARK-3067] JobProgressPage could not show Fair Scheduler Pools section sometimes
cbcba66 [YanTangZhai] Merge pull request #3 from apache/master
aac7f7b [yantangzhai] [SPARK-3067] JobProgressPage could not show Fair Scheduler Pools section sometimes
cdef539 [YanTangZhai] Merge pull request #1 from apache/master
[SPARK-3973] Print call site information for broadcasts

Its hard to debug which broadcast variables refer to what in a big codebase. Printing call site information helps in debugging.

Author: Shivaram Venkataraman <shivaram@cs.berkeley.edu>

Closes #2829 from shivaram/spark-broadcast-print and squashes the following commits:

cd6dbdf [Shivaram Venkataraman] Print call site information for broadcasts
[SPARK-3935][Core] log the number of records that has been written

There is a unused variable(count) in saveAsHadoopDataset in PairRDDFunctions.scala. The initial idea of this variable seems to count the number of records, so I am adding a log statement to log the number of records that has been written to the writer.

Author: likun <jacky.likun@huawei.com>
Author: jackylk <jacky.likun@huawei.com>

Closes #2791 from jackylk/SPARK-3935 and squashes the following commits:

a874047 [jackylk] removing the unused variable in PairRddFunctions.scala
3bf43c7 [likun] log the number of records has been written
[SPARK-3979] [yarn] Use fs's default replication.

This avoids issues when HDFS is configured in a way that would not
allow the hardcoded default replication of "3".

Note: getDefaultReplication(Path) was added in 0.23.3, and the oldest
one available on Maven Central is 0.23.7, so I chose to not add code
to access that method via reflection.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #2831 from vanzin/SPARK-3979 and squashes the following commits:

b0e3a97 [Marcelo Vanzin] [SPARK-3979] [yarn] Use fs's default replication.
[SPARK-3855][SQL] Preserve the result attribute of python UDFs though transformations

In the current implementation it was possible for the reference to change after analysis.

Author: Michael Armbrust <michael@databricks.com>

Closes #2717 from marmbrus/pythonUdfResults and squashes the following commits:

da14879 [Michael Armbrust] Fix test
6343bcb [Michael Armbrust] add test
9533286 [Michael Armbrust] Correctly preserve the result attribute of python UDFs though transformations
[SPARK-3985] [Examples] fix file path using os.path.join

Author: Daoyuan Wang <daoyuan.wang@intel.com>

Closes #2834 from adrian-wang/sqlpypath and squashes the following commits:

da7aa95 [Daoyuan Wang] fix file path using path.join
[SPARK-3934] [SPARK-3918] [mllib]  Bug fixes for RandomForest, DecisionTree

SPARK-3934: When run with a mix of unordered categorical and continuous features, on multiclass classification, RandomForest fails. The bug is in the sanity checks in getFeatureOffset and getLeftRightFeatureOffsets, which use the wrong indices for checking whether features are unordered.
Fix: Remove the sanity checks since they are not really needed, and since they would require DTStatsAggregator to keep track of an extra set of indices (for the feature subset).

Added test to RandomForestSuite which failed with old version but now works.

SPARK-3918: Added baggedInput.unpersist at end of training.

Also:
* I removed DTStatsAggregator.isUnordered since it is no longer used.
* DecisionTreeMetadata: Added logWarning when maxBins is automatically reduced.
* Updated DecisionTreeRunner to explicitly fix the test data to have the same number of features as the training data.  This is a temporary fix which should eventually be replaced by pre-indexing both datasets.
* RandomForestModel: Updated toString to print total number of nodes in forest.
* Changed Predict class to be public DeveloperApi.  This was necessary to allow users to create their own trees by hand (for testing).

CC: mengxr  manishamde chouqin codedeft  Just notifying you of these small bug fixes.

Author: Joseph K. Bradley <joseph.kurata.bradley@gmail.com>

Closes #2785 from jkbradley/dtrunner-update and squashes the following commits:

9132321 [Joseph K. Bradley] merged with master, fixed imports
9dbd000 [Joseph K. Bradley] Merge remote-tracking branch 'upstream/master' into dtrunner-update
e116473 [Joseph K. Bradley] Changed Predict class to be public DeveloperApi.
f502e65 [Joseph K. Bradley] bug fix for SPARK-3934
7f3d60f [Joseph K. Bradley] Merge remote-tracking branch 'upstream/master' into dtrunner-update
ba567ab [Joseph K. Bradley] Changed DTRunner to load test data using same number of features as in training data.
4e88c1f [Joseph K. Bradley] changed RF toString to print total number of nodes
SPARK-3926 [CORE] Result of JavaRDD.collectAsMap() is not Serializable

Make JavaPairRDD.collectAsMap result Serializable since Java Maps generally are

Author: Sean Owen <sowen@cloudera.com>

Closes #2805 from srowen/SPARK-3926 and squashes the following commits:

ecb78ee [Sean Owen] Fix conflict between java.io.Serializable and use of Scala's Serializable
f4717f9 [Sean Owen] Oops, fix compile problem
ae1b36f [Sean Owen] Expand to cover Maps returned from other Java API methods as well
51c26c2 [Sean Owen] Make JavaPairRDD.collectAsMap result Serializable since Java Maps generally are
[SPARK-3952] [Streaming] [PySpark] add Python examples in Streaming Programming Guide

Having Python examples in Streaming Programming Guide.

Also add RecoverableNetworkWordCount example.

Author: Davies Liu <davies.liu@gmail.com>
Author: Davies Liu <davies@databricks.com>

Closes #2808 from davies/pyguide and squashes the following commits:

8d4bec4 [Davies Liu] update readme
26a7e37 [Davies Liu] fix format
3821c4d [Davies Liu] address comments, add missing file
7e4bb8a [Davies Liu] add Python examples in Streaming Programming Guide
[SPARK-2546] Clone JobConf for each task (branch-1.0 / 1.1 backport)

This patch attempts to fix SPARK-2546 in `branch-1.0` and `branch-1.1`.  The underlying problem is that thread-safety issues in Hadoop Configuration objects may cause Spark tasks to get stuck in infinite loops.  The approach taken here is to clone a new copy of the JobConf for each task rather than sharing a single copy between tasks.  Note that there are still Configuration thread-safety issues that may affect the driver, but these seem much less likely to occur in practice and will be more complex to fix (see discussion on the SPARK-2546 ticket).

This cloning is guarded by a new configuration option (`spark.hadoop.cloneConf`) and is disabled by default in order to avoid unexpected performance regressions for workloads that are unaffected by the Configuration thread-safety issues.

Author: Josh Rosen <joshrosen@apache.org>

Closes #2684 from JoshRosen/jobconf-fix-backport and squashes the following commits:

f14f259 [Josh Rosen] Add configuration option to control cloning of Hadoop JobConf.
b562451 [Josh Rosen] Remove unused jobConfCacheKey field.
dd25697 [Josh Rosen] [SPARK-2546] [1.0 / 1.1 backport] Clone JobConf for each task.

(cherry picked from commit 2cd40db2b3ab5ddcb323fd05c171dbd9025f9e71)
Signed-off-by: Josh Rosen <joshrosen@databricks.com>

Conflicts:
	core/src/main/scala/org/apache/spark/rdd/HadoopRDD.scala