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
[SPARK-3902] [SPARK-3590] Stabilize AsynRDDActions and add Java API

This PR adds a Java API for AsyncRDDActions and promotes the API from `Experimental` to stable.

Author: Josh Rosen <joshrosen@apache.org>
Author: Josh Rosen <joshrosen@databricks.com>

Closes #2760 from JoshRosen/async-rdd-actions-in-java and squashes the following commits:

0d45fbc [Josh Rosen] Whitespace fix.
ad3ae53 [Josh Rosen] Merge remote-tracking branch 'origin/master' into async-rdd-actions-in-java
c0153a5 [Josh Rosen] Remove unused variable.
e8e2867 [Josh Rosen] Updates based on Marcelo's review feedback
7a1417f [Josh Rosen] Removed unnecessary java.util import.
6f8f6ac [Josh Rosen] Fix import ordering.
ff28e49 [Josh Rosen] Add MiMa excludes and fix a scalastyle error.
346e46e [Josh Rosen] [SPARK-3902] Stabilize AsyncRDDActions; add Java API.
[SPARK-3948][Shuffle]Fix stream corruption bug in sort-based shuffle

Kernel 2.6.32 bug will lead to unexpected behavior of transferTo in copyStream, and this will corrupt the shuffle output file in sort-based shuffle, which will somehow introduce PARSING_ERROR(2), deserialization error or offset out of range. Here fix this by adding append flag, also add some position checking code. Details can be seen in [SPARK-3948](https://issues.apache.org/jira/browse/SPARK-3948).

Author: jerryshao <saisai.shao@intel.com>

Closes #2824 from jerryshao/SPARK-3948 and squashes the following commits:

be0533a [jerryshao] Address the comments
a82b184 [jerryshao] add configuration to control the NIO way of copying stream
e17ada2 [jerryshao] Fix kernel 2.6.32 bug led unexpected behavior of transferTo
[SPARK-4010][Web UI]Spark UI returns 500 in yarn-client mode

The problem caused by #1966
CC YanTangZhai andrewor14

Author: GuoQiang Li <witgo@qq.com>

Closes #2858 from witgo/SPARK-4010 and squashes the following commits:

9866fbf [GuoQiang Li] Spark UI returns 500 in yarn-client mode
[SPARK-3986][SQL] Fix package names to fit their directory names.

Package names of 2 test suites are different from their directory names.
- `GeneratedEvaluationSuite`
- `GeneratedMutableEvaluationSuite`

Author: Takuya UESHIN <ueshin@happy-camper.st>

Closes #2835 from ueshin/issues/SPARK-3986 and squashes the following commits:

fa2cc05 [Takuya UESHIN] Fix package names to fit their directory names.
[SPARK-3736] Workers reconnect when disassociated from the master.

Before, if the master node is killed and restarted, the worker nodes
would not attempt to reconnect to the Master. Therefore, when the Master
node was restarted, the worker nodes needed to be restarted as well.

Now, when the Master node is disconnected, the worker nodes will
continuously ping the master node in attempts to reconnect to it. Once
the master node restarts, it will detect one of the registration
requests from its former workers. The result is that the cluster
re-enters a healthy state.

In addition, when the master does not receive a heartbeat from the
worker, the worker was removed; however, when the worker sent a
heartbeat to the master, the master used to ignore the heartbeat. Now,
a master that receives a heartbeat from a worker that had been
disconnected will request the worker to re-attempt the registration
process, at which point the worker will send a RegisterWorker request
and be re-connected accordingly.

Re-connection attempts per worker are submitted every N seconds, where N
is configured by the property spark.worker.reconnect.interval - this has
a default of 60 seconds right now.

Author: mcheah <mcheah@palantir.com>

Closes #2828 from mccheah/reconnect-dead-workers and squashes the following commits:

83f8bc9 [mcheah] [SPARK-3736] More informative log message, and fixing some indentation.
fe0e02f [mcheah] [SPARK-3736] Moving reconnection logic to registerWithMaster().
94ddeca [mcheah] [SPARK-3736] Changing a log warning to a log info.
a698e35 [mcheah] [SPARK-3736] Addressing PR comment to make some defs private.
b9a3077 [mcheah] [SPARK-3736] Addressing PR comments related to reconnection.
2ad5ed5 [mcheah] [SPARK-3736] Cancel attempts to reconnect if the master changes.
b5b34af [mcheah] [SPARK-3736] Workers reconnect when disassociated from the master.
[SPARK-3207][MLLIB]Choose splits for continuous features in DecisionTree more adaptively

DecisionTree splits on continuous features by choosing an array of values from a subsample of the data.
Currently, it does not check for identical values in the subsample, so it could end up having multiple copies of the same split. In this PR, we choose splits for a continuous feature in 3 steps:

1. Sort sample values for this feature
2. Get number of occurrence of each distinct value
3. Iterate the value count array computed in step 2 to choose splits.

After find splits, `numSplits` and `numBins` in metadata will be updated.

CC: mengxr manishamde jkbradley, please help me review this, thanks.

Author: Qiping Li <liqiping1991@gmail.com>
Author: chouqin <liqiping1991@gmail.com>
Author: liqi <liqiping1991@gmail.com>
Author: qiping.lqp <qiping.lqp@alibaba-inc.com>

Closes #2780 from chouqin/dt-findsplits and squashes the following commits:

18d0301 [Qiping Li] check explicitly findsplits return distinct splits
8dc28ab [chouqin] remove blank lines
ffc920f [chouqin] adjust code based on comments and add more test cases
9857039 [chouqin] Merge branch 'master' of https://github.com/apache/spark into dt-findsplits
d353596 [qiping.lqp] fix pyspark doc test
9e64699 [Qiping Li] fix random forest unit test
3c72913 [Qiping Li] fix random forest unit test
092efcb [Qiping Li] fix bug
f69f47f [Qiping Li] fix bug
ab303a4 [Qiping Li] fix bug
af6dc97 [Qiping Li] fix bug
2a8267a [Qiping Li] fix bug
c339a61 [Qiping Li] fix bug
369f812 [Qiping Li] fix style
8f46af6 [Qiping Li] add comments and unit test
9e7138e [Qiping Li] Merge branch 'dt-findsplits' of https://github.com/chouqin/spark into dt-findsplits
1b25a35 [Qiping Li] Merge branch 'master' of https://github.com/apache/spark into dt-findsplits
0cd744a [liqi] fix bug
3652823 [Qiping Li] fix bug
af7cb79 [Qiping Li] Choose splits for continuous features in DecisionTree more adaptively
[SPARK-3906][SQL] Adds multiple join support for SQLContext

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

Closes #2767 from liancheng/multi-join and squashes the following commits:

9dc0d18 [Cheng Lian] Adds multiple join support for SQLContext
[SPARK-3800][SQL] Clean aliases from grouping expressions

Author: Michael Armbrust <michael@databricks.com>

Closes #2658 from marmbrus/nestedAggs and squashes the following commits:

862b763 [Michael Armbrust] Merge remote-tracking branch 'origin/master' into nestedAggs
3234521 [Michael Armbrust] Merge remote-tracking branch 'origin/master' into nestedAggs
8b06fdc [Michael Armbrust] possible fix for grouping on nested fields