Unit test is still in Scala.

Author: Reynold Xin <rxin@databricks.com>

Closes #6738 from rxin/utf8string-java and squashes the following commits:

562dc6e [Reynold Xin] Flag...
98e600b [Reynold Xin] Another try with encoding setting ..
cfa6bdf [Reynold Xin] Merge branch 'master' into utf8string-java
a3b124d [Reynold Xin] Try different UTF-8 encoded characters.
1ff7c82 [Reynold Xin] Enable UTF-8 encoding.
82d58cc [Reynold Xin] Reset run-tests.
2cb3c69 [Reynold Xin] Use utf-8 encoding in set bytes.
53f8ef4 [Reynold Xin] Hack Jenkins to run one test.
9a48e8d [Reynold Xin] Fixed runtime compilation error.
911c450 [Reynold Xin] Moved unit test also to Java.
4eff7bd [Reynold Xin] Improved unit test coverage.
8e89a3c [Reynold Xin] Fixed tests.
77c64bd [Reynold Xin] Fixed string type codegen.
ffedb62 [Reynold Xin] Code review feedback.
0967ce6 [Reynold Xin] Fixed import ordering.
45a123d [Reynold Xin] [SPARK-8286] Rewrite UTF8String in Java and move it into unsafe package.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #6766 from vanzin/SPARK-6511 and squashes the following commits:

49f0f67 [Marcelo Vanzin] [SPARK-6511] [docs] Fix example command in hadoop-provided docs.

Eliminate the following noisy logs for `UISeleniumSuite`:
```
15/05/07 10:09:50.196 pool-1-thread-1-ScalaTest-running-UISeleniumSuite WARN DefaultCssErrorHandler: CSS error: 'http://192.168.0.170:4040/static/bootstrap.min.css' [793:167] Error in style rule. (Invalid token "*". Was expecting one of: <EOF>, <S>, <IDENT>, "}", ";".)
15/05/07 10:09:50.196 pool-1-thread-1-ScalaTest-running-UISeleniumSuite WARN DefaultCssErrorHandler: CSS warning: 'http://192.168.0.170:4040/static/bootstrap.min.css' [793:167] Ignoring the following declarations in this rule.
15/05/07 10:09:50.197 pool-1-thread-1-ScalaTest-running-UISeleniumSuite WARN DefaultCssErrorHandler: CSS error: 'http://192.168.0.170:4040/static/bootstrap.min.css' [799:325] Error in style rule. (Invalid token "*". Was expecting one of: <EOF>, <S>, <IDENT>, "}", ";".)
15/05/07 10:09:50.197 pool-1-thread-1-ScalaTest-running-UISeleniumSuite WARN DefaultCssErrorHandler: CSS warning: 'http://192.168.0.170:4040/static/bootstrap.min.css' [799:325] Ignoring the following declarations in this rule.
15/05/07 10:09:50.198 pool-1-thread-1-ScalaTest-running-UISeleniumSuite WARN DefaultCssErrorHandler: CSS error: 'http://192.168.0.170:4040/static/bootstrap.min.css' [805:18] Error in style rule. (Invalid token "*". Was expecting one of: <EOF>, <S>, <IDENT>, "}", ";".)
15/05/07 10:09:50.198 pool-1-thread-1-ScalaTest-running-UISeleniumSuite WARN DefaultCssErrorHandler: CSS warning: 'http://192.168.0.170:4040/static/bootstrap.min.css' [805:18] Ignoring the following declarations in this rule.
```

Author: zsxwing <zsxwing@gmail.com>

Closes #5983 from zsxwing/SPARK-7444 and squashes the following commits:

4202728 [zsxwing] Add SparkUICssErrorHandler for all tests
d1398ad [zsxwing] Merge remote-tracking branch 'origin/master' into SPARK-7444
7bb7f11 [zsxwing] Merge branch 'master' into SPARK-7444
a59f40e [zsxwing] Eliminate noisy css warn/error logs for UISeleniumSuite

```
create table t1 (a int, b string) as select key, value from src;

desc t1;
key	int	NULL
value	string	NULL
```

Thus Hive doesn't support specifying the column list for target table in CTAS, however, we should either throwing exception explicity, or supporting the this feature, we just pick up the later one, which seems useful and straightforward.

Author: Cheng Hao <hao.cheng@intel.com>

Closes #6458 from chenghao-intel/ctas_column and squashes the following commits:

d1fa9b6 [Cheng Hao] bug in unittest
4e701aa [Cheng Hao] update as feedback
f305ec1 [Cheng Hao] support specifying the column list for target table in CTAS

Will send another PR for `branch-1.4`

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

Closes #6764 from shivaram/SPARK-8310 and squashes the following commits:

d8cd3b3 [Shivaram Venkataraman] This updates the master branch EC2 versions

This PR fix a few small issues about codgen:

1. cast decimal to boolean
2. do not inline literal with null
3. improve SpecificRow.equals()
4. test expressions with optimized express
5. fix compare with BinaryType

cc rxin chenghao-intel

Author: Davies Liu <davies@databricks.com>

Closes #6755 from davies/fix_codegen and squashes the following commits:

ef27343 [Davies Liu] address comments
6617ea6 [Davies Liu] fix scala tyle
70b7dda [Davies Liu] improve codegen

Spark SQL does not support timezone, and Pyrolite does not support timezone well. This patch will convert datetime into POSIX timestamp (without confusing of timezone), which is used by SQL. If the datetime object does not have timezone, it's treated as local time.

The timezone in RDD will be lost after one round trip, all the datetime from SQL will be local time.

Because of Pyrolite, datetime from SQL only has precision as 1 millisecond.

This PR also drop the timezone in date, convert it to number of days since epoch (used in SQL).

Author: Davies Liu <davies@databricks.com>

Closes #6250 from davies/tzone and squashes the following commits:

44d8497 [Davies Liu] add timezone support for DateType
99d9d9c [Davies Liu] use int for timestamp
10aa7ca [Davies Liu] Merge branch 'master' of github.com:apache/spark into tzone
6a29aa4 [Davies Liu] support datetime with timezone

This change is a simple one and specifies a stack size of 4096k instead of the vendor default for Java tests (the defaults vary between Java vendors). This remedies test failures observed with JavaALSSuite with IBM and Oracle Java owing to a lower default size in comparison to the size with OpenJDK. 4096k is a suitable default where the tests pass with each Java vendor tested. The alternative is to reduce the number of iterations in the test (no observed failures with 5 iterations instead of 15).

-Xss works with Oracle's HotSpot VM, IBM's J9 VM and OpenJDK (IcedTea).

I have ensured this does not have any negative implications for other tests.

Author: Adam Roberts <aroberts@uk.ibm.com>
Author: a-roberts <aroberts@uk.ibm.com>

Closes #6727 from a-roberts/IncJavaStackSize and squashes the following commits:

ab40aea [Adam Roberts] Specify stack size for SBT builds
5032d8d [a-roberts] Update pom.xml

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

This patch had conflicts when merged, resolved by
Committer: Reynold Xin <rxin@databricks.com>

Closes #6718 from adrian-wang/udflog2 and squashes the following commits:

3909f48 [Daoyuan Wang] math function: log2

Author: Cheng Hao <hao.cheng@intel.com>

Closes #6724 from chenghao-intel/length and squashes the following commits:

aaa3c31 [Cheng Hao] revert the additional change
97148a9 [Cheng Hao] remove the codegen testing temporally
ae08003 [Cheng Hao] update the comments
1eb1fd1 [Cheng Hao] simplify the code as commented
3e92d32 [Cheng Hao] use the selectExpr in unit test intead of SQLQuery
3c729aa [Cheng Hao] fix bug for constant null value in codegen
3641f06 [Cheng Hao] keep the length() method for registered function
8e30171 [Cheng Hao] update the code as comment
db604ae [Cheng Hao] Add code gen support
548d2ef [Cheng Hao] register the length()
09a0738 [Cheng Hao] add length support

Currently we only support `Seq[Expression]`, we should handle cases like `Seq[Seq[Expression]]` so that we can remove the unnecessary `GroupExpression`.

Author: Wenchen Fan <cloud0fan@outlook.com>

Closes #6706 from cloud-fan/clean and squashes the following commits:

60a1193 [Wenchen Fan] support nested expression sequence and remove GroupExpression

    case cs  CombineSum(expr) =>
        val calcType = expr.dataType
          expr.dataType match {
            case DecimalType.Fixed(_, _) =>
              DecimalType.Unlimited
            case _ =>
              expr.dataType
          }
calcType is always expr.dataType. credits are all belong to IntelliJ

Author: navis.ryu <navis@apache.org>

Closes #6736 from navis/SPARK-8285 and squashes the following commits:

20382c1 [navis.ryu] [SPARK-8285] [SQL] CombineSum should be calculated as unlimited decimal first

This PR change to use Long as internal type for TimestampType for efficiency, which means it will the precision below 100ns.

Author: Davies Liu <davies@databricks.com>

Closes #6733 from davies/timestamp and squashes the following commits:

d9565fa [Davies Liu] remove print
65cf2f1 [Davies Liu] fix Timestamp in SparkR
86fecfb [Davies Liu] disable two timestamp tests
8f77ee0 [Davies Liu] fix scala style
246ee74 [Davies Liu] address comments
309d2e1 [Davies Liu] use Long for TimestampType in SQL

Test cases for both StreamingLinearRegression and StreamingLogisticRegression, and code fix.

Edit:
This contribution is my original work and I license the work to the project under the project's open source license.

Author: Paavo <pparkkin@gmail.com>

Closes #6713 from pparkkin/streamingmodel-empty-rdd and squashes the following commits:

ff5cd78 [Paavo] Update strings to use interpolation.
db234cf [Paavo] Use !rdd.isEmpty.
54ad89e [Paavo] Test case for empty stream.
393e36f [Paavo] Ignore empty RDDs.
0bfc365 [Paavo] Test case for empty stream.

Set preferred locations for reduce tasks.
The basic design is that we maintain a map from reducerId to a list of (sizes, locations) for each
shuffle. We then set the preferred locations to be any machines that have 20% of more of the output
that needs to be read by the reduce task.  This will result in at most 5 preferred locations for
each reduce task.

Selecting the preferred locations involves O(# map tasks * # reduce tasks) computation, so we
restrict this feature to cases where we have fewer than 1000 map tasks and 1000 reduce tasks.

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

Closes #6652 from shivaram/reduce-locations and squashes the following commits:

492e25e [Shivaram Venkataraman] Remove unused import
2ef2d39 [Shivaram Venkataraman] Address code review comments
897a914 [Shivaram Venkataraman] Remove unused hash map
f5be578 [Shivaram Venkataraman] Use fraction of map outputs to determine locations Also removes caching of preferred locations to make the API cleaner
68bc29e [Shivaram Venkataraman] Fix line length
1090b58 [Shivaram Venkataraman] Change flag name
77ce7d8 [Shivaram Venkataraman] Merge branch 'master' of https://github.com/apache/spark into reduce-locations
e5d56bd [Shivaram Venkataraman] Add flag to turn off locality for shuffle deps
6cfae98 [Shivaram Venkataraman] Filter out zero blocks, rename variables
9d5831a [Shivaram Venkataraman] Address some more comments
8e31266 [Shivaram Venkataraman] Fix style
0df3180 [Shivaram Venkataraman] Address code review comments
e7d5449 [Shivaram Venkataraman] Fix merge issues
ad7cb53 [Shivaram Venkataraman] Merge branch 'master' of https://github.com/apache/spark into reduce-locations
df14cee [Shivaram Venkataraman] Merge branch 'master' of https://github.com/apache/spark into reduce-locations
5093aea [Shivaram Venkataraman] Merge branch 'master' of https://github.com/apache/spark into reduce-locations
0171d3c [Shivaram Venkataraman] Merge branch 'master' of https://github.com/apache/spark into reduce-locations
bc4dfd6 [Shivaram Venkataraman] Merge branch 'master' of https://github.com/apache/spark into reduce-locations
774751b [Shivaram Venkataraman] Fix bug introduced by line length adjustment
34d0283 [Shivaram Venkataraman] Fix style issues
3b464b7 [Shivaram Venkataraman] Set preferred locations for reduce tasks This is another attempt at #1697 addressing some of the earlier concerns. This adds a couple of thresholds based on number map and reduce tasks beyond which we don't use preferred locations for reduce tasks.

In client mode, if yarn was shut down with spark application running, the application will hang up after several retries(default: 30) because the exception throwed by YarnClientImpl could not be caught by upper level, we should exit in case that user can not be aware that.

The exception we wanna catch is [here](https://github.com/apache/hadoop/blob/branch-2.7.0/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/retry/RetryInvocationHandler.java#L122), and I try to fix it refer to [MR](https://github.com/apache/hadoop/blob/branch-2.7.0/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient/src/main/java/org/apache/hadoop/mapred/ClientServiceDelegate.java#L320).

Author: WangTaoTheTonic <wangtao111@huawei.com>

Closes #6717 from WangTaoTheTonic/SPARK-8273 and squashes the following commits:

28752d6 [WangTaoTheTonic] catch the throwed exception

SPARK_JAVA_OPTS was missed in reconstructing the launcher part, we should add it back so process launched by spark-class could read it properly. And so does `SPARK_DRIVER_MEMORY`.

The missing part is [here](https://github.com/apache/spark/blob/1c30afdf94b27e1ad65df0735575306e65d148a1/bin/spark-class#L97).

Author: WangTaoTheTonic <wangtao111@huawei.com>
Author: Tao Wang <wangtao111@huawei.com>

Closes #6741 from WangTaoTheTonic/SPARK-8290 and squashes the following commits:

bd89f0f [Tao Wang] make sure the memory setting is right too
e313520 [WangTaoTheTonic] spark class command builder need read SPARK_JAVA_OPTS

1. Add `log4j-defaults-repl.properties` that has log level WARN.
2. When logging is initialized, check whether inside the REPL. If so, use `log4j-defaults-repl.properties`.
3. Print the following information if using `log4j-defaults-repl.properties`:
```
Using Spark's repl log4j profile: org/apache/spark/log4j-defaults-repl.properties
To adjust logging level use sc.setLogLevel("INFO")
```

Author: zsxwing <zsxwing@gmail.com>

Closes #6734 from zsxwing/log4j-repl and squashes the following commits:

3835eff [zsxwing] Change default log level to WARN in the REPL

The root cause of SPARK-7527 is `createNullValue` returns an incompatible value `Byte(0)` for `char` and `boolean`.

This PR fixes it and corrects the class name of the main class, and also adds an unit test to demonstrate it.

Author: zsxwing <zsxwing@gmail.com>

Closes #6735 from zsxwing/SPARK-7527 and squashes the following commits:

bbdb271 [zsxwing] Use pattern match in createNullValue
b0a0e7e [zsxwing] Remove the noisy in the test output
903e269 [zsxwing] Remove the code for Utils.isInInterpreter == false
5f92dc1 [zsxwing] Fix createNullValue to return the correct null values and REPL mode detection

IBM Java has an extra method when we do getStackTrace(): this is "getStackTraceImpl", a native method. This causes two tests to fail within "DStreamScopeSuite" when running with IBM Java. Instead of "map" or "filter" being the method names found, "getStackTrace" is returned. This commit addresses such an issue by using dropWhile. Given that our current method is withScope, we look for the next method that isn't ours: we don't care about methods that come before us in the stack trace: e.g. getStackTrace (regardless of how many levels this might go).

IBM:
java.lang.Thread.getStackTraceImpl(Native Method)
java.lang.Thread.getStackTrace(Thread.java:1117)
org.apache.spark.rdd.RDDOperationScope$.withScope(RDDOperationScope.scala:104)

Oracle:
PRINTING STACKTRACE!!!
java.lang.Thread.getStackTrace(Thread.java:1552)
org.apache.spark.rdd.RDDOperationScope$.withScope(RDDOperationScope.scala:106)

I've tested this with Oracle and IBM Java, no side effects for other tests introduced.

Author: Adam Roberts <aroberts@uk.ibm.com>
Author: a-roberts <aroberts@uk.ibm.com>

Closes #6740 from a-roberts/RDDScopeStackCrawlFix and squashes the following commits:

13ce390 [Adam Roberts] Ensure consistency with String equality checking
a4fc0e0 [a-roberts] Update RDDOperationScope.scala

Read number of threads for RBackend from configuration.

[SPARK-8282] #comment Linking with JIRA

Author: Hossein <hossein@databricks.com>

Closes #6730 from falaki/SPARK-8282 and squashes the following commits:

33b3d98 [Hossein] Documented new config parameter
70f2a9c [Hossein] Fixing import
ec44225 [Hossein] Read number of threads for RBackend from configuration

The bug description is a little misleading: the actual issue is that
.py files are not handled correctly when distributed by YARN. They're
added to "spark.submit.pyFiles", which, when processed by context.py,
explicitly whitelists certain extensions (see PACKAGE_EXTENSIONS),
and that does not include .py files.

On top of that, archives were not handled at all! They made it to the
driver's python path, but never made it to executors, since the mechanism
used to propagate their location (spark.submit.pyFiles) only works on
the driver side.

So, instead, ignore "spark.submit.pyFiles" and just build PYTHONPATH
correctly for both driver and executors. Individual .py files are
placed in a subdirectory of the container's local dir in the cluster,
which is then added to the python path. Archives are added directly.

The change, as a side effect, ends up solving the symptom described
in the bug. The issue was not that the files were not being distributed,
but that they were never made visible to the python application
running under Spark.

Also included is a proper unit test for running python on YARN, which
broke in several different ways with the previous code.

A short walk around of the changes:
- SparkSubmit does not try to be smart about how YARN handles python
  files anymore. It just passes down the configs to the YARN client
  code.
- The YARN client distributes python files and archives differently,
  placing the files in a subdirectory.
- The YARN client now sets PYTHONPATH for the processes it launches;
  to properly handle different locations, it uses YARN's support for
  embedding env variables, so to avoid YARN expanding those at the
  wrong time, SparkConf is now propagated to the AM using a conf file
  instead of command line options.
- Because the Client initialization code is a maze of implicit
  dependencies, some code needed to be moved around to make sure
  all needed state was available when the code ran.
- The pyspark tests in YarnClusterSuite now actually distribute and try
  to use both a python file and an archive containing a different python
  module. Also added a yarn-client tests for completeness.
- I cleaned up some of the code around distributing files to YARN, to
  avoid adding more copied & pasted code to handle the new files being
  distributed.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #6360 from vanzin/SPARK-5479 and squashes the following commits:

bcaf7e6 [Marcelo Vanzin] Feedback.
c47501f [Marcelo Vanzin] Fix yarn-client mode.
46b1d0c [Marcelo Vanzin] Merge branch 'master' into SPARK-5479
c743778 [Marcelo Vanzin] Only pyspark cares about python archives.
c8e5a82 [Marcelo Vanzin] Actually run pyspark in client mode.
705571d [Marcelo Vanzin] Move some code to the YARN module.
1dd4d0c [Marcelo Vanzin] Review feedback.
71ee736 [Marcelo Vanzin] Merge branch 'master' into SPARK-5479
220358b [Marcelo Vanzin] Scalastyle.
cdbb990 [Marcelo Vanzin] Merge branch 'master' into SPARK-5479
7fe3cd4 [Marcelo Vanzin] No need to distribute primary file to executors.
09045f1 [Marcelo Vanzin] Style.
943cbf4 [Marcelo Vanzin] [SPARK-5479] [yarn] Handle --py-files correctly in YARN.

Author: Cheng Lian <lian@databricks.com>

Closes #6749 from liancheng/java-sample-fix and squashes the following commits:

5b44585 [Cheng Lian] Fixes a minor Java example error in SQL programming guide

Changed ```SparkEnv.actorSystem``` to be a function such that we can use the deprecated flag with it and added a deprecated message.

Author: Ilya Ganelin <ilya.ganelin@capitalone.com>

Closes #6731 from ilganeli/SPARK-7996 and squashes the following commits:

be43817 [Ilya Ganelin] Restored to val
9ed89e7 [Ilya Ganelin] Added a version info for deprecation
9610b08 [Ilya Ganelin] Converted actorSystem to function and added deprecated flag

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

Closes #6716 from adrian-wang/epi and squashes the following commits:

e2e8dbd [Daoyuan Wang] move tests
11b351c [Daoyuan Wang] add tests and remove pu
db331c9 [Daoyuan Wang] py style
599ddd8 [Daoyuan Wang] add py
e6783ef [Daoyuan Wang] register function
82d426e [Daoyuan Wang] add function entry
dbf3ab5 [Daoyuan Wang] add PI and E

This is a followup to #6712.

Author: Reynold Xin <rxin@databricks.com>

Closes #6739 from rxin/6712-followup and squashes the following commits:

fd9acfb [Reynold Xin] [SPARK-7886] Added unit test for HAVING aggregate pushdown.

This builds on #6710 and also uses FunctionRegistry for function lookup in HiveContext.

Author: Reynold Xin <rxin@databricks.com>

Closes #6712 from rxin/udf-registry-hive and squashes the following commits:

f4c2df0 [Reynold Xin] Fixed style violation.
0bd4127 [Reynold Xin] Fixed Python UDFs.
f9a0378 [Reynold Xin] Disable one more test.
5609494 [Reynold Xin] Disable some failing tests.
4efea20 [Reynold Xin] Don't check children resolved for UDF resolution.
2ebe549 [Reynold Xin] Removed more hardcoded functions.
aadce78 [Reynold Xin] [SPARK-7886] Use FunctionRegistry for built-in expressions in HiveContext.

Just replaced mutable.HashMap to ConcurrentHashMap

Author: navis.ryu <navis@apache.org>

Closes #6699 from navis/SPARK-7792 and squashes the following commits:

f03654a [navis.ryu] [SPARK-7792] [SQL] HiveContext registerTempTable not thread safe

This provides preliminary documentation pointing out how to use the
Hadoop free builds. I am hoping over time this list can grow to
include most of the popular Hadoop distributions.

Getting more people using these builds will help us long term reduce
the number of binaries we build.

Author: Patrick Wendell <patrick@databricks.com>

Closes #6729 from pwendell/hadoop-provided and squashes the following commits:

1113b76 [Patrick Wendell] [SPARK-6511] [Documentation] Explain how to use Hadoop provided builds

Just as a safeguard against DOM rewriting.

Author: Andrew Or <andrew@databricks.com>

Closes #6732 from andrewor14/dag-viz-trim and squashes the following commits:

7e9bacb [Andrew Or] [MINOR] [UI] DAG visualization: trim whitespace from input

There is a mistake in the URLs of the Scala section of FP-Growth in the MLlib Frequent Pattern Mining documentation. The URL points to https://spark.apache.org/docs/latest/api/java/org/apache/spark/mllib/fpm/FPGrowth.html which is the Java's API, the link should point to the Scala API https://spark.apache.org/docs/latest/api/scala/index.html#org.apache.spark.mllib.fpm.FPGrowth

There's another mistake in the FP-GrowthModel in the same section, the link points, again, to the Java's API https://spark.apache.org/docs/latest/api/java/org/apache/spark/mllib/fpm/FPGrowthModel.html, the link should point to the Scala API https://spark.apache.org/docs/latest/api/scala/index.html#org.apache.spark.mllib.fpm.FPGrowthModel

Author: FavioVazquez <favio.vazquezp@gmail.com>

Closes #6722 from FavioVazquez/fix-wrog-urls-mllib-fpgrowth and squashes the following commits:

e1ca54d [FavioVazquez] - Fixed wrong URLs in MLlib Frequent Pattern Mining, FP-Growth Scala section
ad882a3 [FavioVazquez] Merge remote-tracking branch 'upstream/master'
f27a20b [FavioVazquez] Merge remote-tracking branch 'upstream/master'
9af7074 [FavioVazquez] Merge remote-tracking branch 'upstream/master'
edab1ef [FavioVazquez] Merge remote-tracking branch 'upstream/master'
b2e2f8c [FavioVazquez] Merge remote-tracking branch 'upstream/master'

Author: MechCoder <manojkumarsivaraj334@gmail.com>

Closes #6720 from MechCoder/empty_model_check and squashes the following commits:

3a07de5 [MechCoder] Remove construct to get weights in StreamingLinearAlgorithm

I noticed there is a duplicated description about WAL.

```
To ensure zero-data loss, you have to additionally enable Write Ahead Logs in Spark Streaming. To ensure zero data loss, enable the Write Ahead Logs (introduced in Spark 1.2).
```

Let's remove the duplication.

I don't file this issue in JIRA because it's minor.

Author: Kousuke Saruta <sarutak@oss.nttdata.co.jp>

Closes #6719 from sarutak/remove-multiple-description and squashes the following commits:

cc9bb21 [Kousuke Saruta] Removed duplicated description about WAL

This patch switches to using FunctionRegistry for built-in expressions. It is based on #6463, but with some work to simplify it along with unit tests.

TODOs for future pull requests:
- Use static registration so we don't need to register all functions every time we start a new SQLContext
- Switch to using this in HiveContext

Author: Reynold Xin <rxin@databricks.com>
Author: Santiago M. Mola <santi@mola.io>

Closes #6710 from rxin/udf-registry and squashes the following commits:

6930822 [Reynold Xin] Fixed Python test.
b802c9a [Reynold Xin] Made UDF case insensitive.
e60d815 [Reynold Xin] Made UDF case insensitive.
852f9c0 [Reynold Xin] Fixed style violation.
e76a3c1 [Reynold Xin] Fixed parser.
52ddaba [Reynold Xin] Fixed compilation.
ee7854f [Reynold Xin] Improved error reporting.
ff906f2 [Reynold Xin] More robust constructor calling.
77b46f1 [Reynold Xin] Simplified the code.
2a2a149 [Reynold Xin] Merge pull request #6463 from smola/SPARK-7886
8616924 [Santiago M. Mola] [SPARK-7886] Add built-in expressions to FunctionRegistry.

Update to Netty 4.0.28-Final

Author: Sean Owen <sowen@cloudera.com>

Closes #6701 from srowen/SPARK-8101 and squashes the following commits:

f3b6369 [Sean Owen] Update to Netty 4.0.28-Final

JIRA: https://issues.apache.org/jira/browse/SPARK-7990

Author: Liang-Chi Hsieh <viirya@gmail.com>

Closes #6616 from viirya/multi_keys_equi_join and squashes the following commits:

cd5c888 [Liang-Chi Hsieh] Import reduce in python3.
c43722c [Liang-Chi Hsieh] For comments.
0400e89 [Liang-Chi Hsieh] Fix scala style.
cc90015 [Liang-Chi Hsieh] Add methods to facilitate equi-join on multiple joining keys.

Author: hqzizania <qian.huang@intel.com>

Closes #6190 from hqzizania/R and squashes the following commits:

1641f9e [hqzizania] fixes and add test units
bb3411a [hqzizania] Convert NAs to null type in SparkR DataFrames

This makes the constructor callable in Python. dbtsai

Author: Xiangrui Meng <meng@databricks.com>

Closes #6709 from mengxr/SPARK-8168 and squashes the following commits:

f871de4 [Xiangrui Meng] Add Python friendly constructor to PipelineModel