## What changes were proposed in this pull request?
Remove deprecated methods for ML.

## How was this patch tested?
Existing tests.

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #15913 from yanboliang/spark-18481.

## What changes were proposed in this pull request?

The nullability of `InputFileName` should be `false`.

## How was this patch tested?

Existing tests.

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

Closes #16007 from ueshin/issues/SPARK-18583.

## What changes were proposed in this pull request?

The expression `in(empty seq)` is invalid in some data source. Since `in(empty seq)` is always false, we should generate `in(empty seq)` to false literal in optimizer.
The sql `SELECT * FROM t WHERE a IN ()` throws a `ParseException` which is consistent with Hive, don't need to change that behavior.

## How was this patch tested?
Add new test case in `OptimizeInSuite`.

Author: jiangxingbo <jiangxb1987@gmail.com>

Closes #15977 from jiangxb1987/isin-empty.

## What changes were proposed in this pull request?

This is a follow-up PR of #15868 to merge `maxConnections` option into `numPartitions` options.

## How was this patch tested?

Pass the existing tests.

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #15966 from dongjoon-hyun/SPARK-18413-2.

## What changes were proposed in this pull request?

Spark Kmeans fit() doesn't cache the RDD which generates a lot of warnings :
 WARN KMeans: The input data is not directly cached, which may hurt performance if its parent RDDs are also uncached.
So, Kmeans should cache the internal rdd before calling the Mllib.Kmeans algo, this helped to improve spark kmeans performance by 14%

https://github.com/ZakariaHili/spark/commit/a9cf905cf7dbd50eeb9a8b4f891f2f41ea672472

hhbyyh
## How was this patch tested?
Pass Kmeans tests and existing tests

Author: Zakaria_Hili <zakahili@gmail.com>
Author: HILI Zakaria <zakahili@gmail.com>

Closes #15965 from ZakariaHili/zakbranch.

## What changes were proposed in this pull request?

In `HyperLogLogPlusPlus`, if the relative error is so small that p >= 19, it will cause ArrayIndexOutOfBoundsException in `THRESHOLDS(p-4)` . We should check `p` and when p >= 19, regress to the original HLL result and use the small range correction they use.

The pr also fixes the upper bound in the log info in `require()`.
The upper bound is computed by:
```
val relativeSD = 1.106d / Math.pow(Math.E, p * Math.log(2.0d) / 2.0d)
```
which is derived from the equation for computing `p`:
```
val p = 2.0d * Math.log(1.106d / relativeSD) / Math.log(2.0d)
```

## How was this patch tested?

add test cases for:
1. checking validity of parameter relatvieSD
2. estimation with smaller relative error so that p >= 19

Author: Zhenhua Wang <wzh_zju@163.com>
Author: wangzhenhua <wangzhenhua@huawei.com>

Closes #15990 from wzhfy/hllppRsd.

[SPARK-3359][BUILD][DOCS] More changes to resolve javadoc 8 errors that will help unidoc/genjavadoc compatibility

## What changes were proposed in this pull request?

This PR only tries to fix things that looks pretty straightforward and were fixed in other previous PRs before.

This PR roughly fixes several things as below:

- Fix unrecognisable class and method links in javadoc by changing it from `[[..]]` to `` `...` ``

  ```
  [error] .../spark/sql/core/target/java/org/apache/spark/sql/streaming/DataStreamReader.java:226: error: reference not found
  [error]    * Loads text files and returns a {link DataFrame} whose schema starts with a string column named
  ```

- Fix an exception annotation and remove code backticks in `throws` annotation

  Currently, sbt unidoc with Java 8 complains as below:

  ```
  [error] .../java/org/apache/spark/sql/streaming/StreamingQuery.java:72: error: unexpected text
  [error]    * throws StreamingQueryException, if <code>this</code> query has terminated with an exception.
  ```

  `throws` should specify the correct class name from `StreamingQueryException,` to `StreamingQueryException` without backticks. (see [JDK-8007644](https://bugs.openjdk.java.net/browse/JDK-8007644)).

- Fix `[[http..]]` to `<a href="http..."></a>`.

  ```diff
  -   * [[https://blogs.oracle.com/java-platform-group/entry/diagnosing_tls_ssl_and_https Oracle
  -   * blog page]].
  +   * <a href="https://blogs.oracle.com/java-platform-group/entry/diagnosing_tls_ssl_and_https">
  +   * Oracle blog page</a>.
  ```

   `[[http...]]` link markdown in scaladoc is unrecognisable in javadoc.

- It seems class can't have `return` annotation. So, two cases of this were removed.

  ```
  [error] .../java/org/apache/spark/mllib/regression/IsotonicRegression.java:27: error: invalid use of return
  [error]    * return New instance of IsotonicRegression.
  ```

- Fix < to `&lt;` and > to `&gt;` according to HTML rules.

- Fix `</p>` complaint

- Exclude unrecognisable in javadoc, `constructor`, `todo` and `groupname`.

## How was this patch tested?

Manually tested by `jekyll build` with Java 7 and 8

```
java version "1.7.0_80"
Java(TM) SE Runtime Environment (build 1.7.0_80-b15)
Java HotSpot(TM) 64-Bit Server VM (build 24.80-b11, mixed mode)
```

```
java version "1.8.0_45"
Java(TM) SE Runtime Environment (build 1.8.0_45-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.45-b02, mixed mode)
```

Note: this does not yet make sbt unidoc suceed with Java 8 yet but it reduces the number of errors with Java 8.

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #15999 from HyukjinKwon/SPARK-3359-errors.

[SPARK-18119][SPARK-CORE] Namenode safemode check is only performed on one namenode which can stuck the startup of SparkHistory server

## What changes were proposed in this pull request?

Instead of using the setSafeMode method that check the first namenode used the one which permitts to check only for active NNs
## How was this patch tested?

manual tests

Please review https://cwiki.apache.org/confluence/display/SPARK/Contributing+to+Spark before opening a pull request.

This commit is contributed by Criteo SA under the Apache v2 licence.

Author: n.fraison <n.fraison@criteo.com>

Closes #15648 from ashangit/SPARK-18119.

## What changes were proposed in this pull request?

NOT BUG, just adjust the position of driver log link to keep the same style with other executors log link.

![image](https://cloud.githubusercontent.com/assets/7402327/20590092/f8bddbb8-b25b-11e6-9aaf-3b5b3073df10.png)

## How was this patch tested?
 no

Author: uncleGen <hustyugm@gmail.com>

Closes #16001 from uncleGen/SPARK-18575.

## What changes were proposed in this pull request?

- Raise Analysis exception when correlated predicates exist in the descendant operators of either operand of a Full outer join in a subquery as well as in a FOJ operator itself
- Raise Analysis exception when correlated predicates exists in a Window operator (a side effect inadvertently introduced by SPARK-17348)

## How was this patch tested?

Run sql/test catalyst/test and new test cases, added to SubquerySuite, showing the reported incorrect results.

Author: Nattavut Sutyanyong <nsy.can@gmail.com>

Closes #16005 from nsyca/FOJ-incorrect.1.

## What changes were proposed in this pull request?
add `setFeaturesCol` and `setPredictionCol` for BiKModel and GMModel
add `setProbabilityCol` for GMModel
## How was this patch tested?
existing tests

Author: Zheng RuiFeng <ruifengz@foxmail.com>

Closes #15957 from zhengruifeng/bikm_set.

## What changes were proposed in this pull request?

This PR addressed the rest comments in #15951.

## How was this patch tested?

Jenkins

Author: Shixiong Zhu <shixiong@databricks.com>

Closes #15997 from zsxwing/SPARK-18510-follow-up.

## What changes were proposed in this pull request?

### The Issue

If I specify my schema when doing
```scala
spark.read
  .schema(someSchemaWherePartitionColumnsAreStrings)
```
but if the partition inference can infer it as IntegerType or I assume LongType or DoubleType (basically fixed size types), then once UnsafeRows are generated, your data will be corrupted.

### Proposed solution

The partition handling code path is kind of a mess. In my fix I'm probably adding to the mess, but at least trying to standardize the code path.

The real issue is that a user that uses the `spark.read` code path can never clearly specify what the partition columns are. If you try to specify the fields in `schema`, we practically ignore what the user provides, and fall back to our inferred data types. What happens in the end is data corruption.

My solution tries to fix this by always trying to infer partition columns the first time you specify the table. Once we find what the partition columns are, we try to find them in the user specified schema and use the dataType provided there, or fall back to the smallest common data type.

We will ALWAYS append partition columns to the user's schema, even if they didn't ask for it. We will only use the data type they provided if they specified it. While this is confusing, this has been the behavior since Spark 1.6, and I didn't want to change this behavior in the QA period of Spark 2.1. We may revisit this decision later.

A side effect of this PR is that we won't need https://github.com/apache/spark/pull/15942 if this PR goes in.

## How was this patch tested?

Regression tests

Author: Burak Yavuz <brkyvz@gmail.com>

Closes #15951 from brkyvz/partition-corruption.

## What changes were proposed in this pull request?

When we try to create the default database, we ask hive to do nothing if it already exists. However, Hive will log an error message instead of doing nothing, and the error message is quite annoying and confusing.

In this PR, we only create default database if it doesn't exist.

## How was this patch tested?

N/A

Author: Wenchen Fan <wenchen@databricks.com>

Closes #15993 from cloud-fan/default-db.

## What changes were proposed in this pull request?
The current implementation of column stats uses the base64 encoding of the internal UnsafeRow format to persist statistics (in table properties in Hive metastore). This is an internal format that is not stable across different versions of Spark and should NOT be used for persistence. In addition, it would be better if statistics stored in the catalog is human readable.

This pull request introduces the following changes:

1. Created a single ColumnStat class to for all data types. All data types track the same set of statistics.
2. Updated the implementation for stats collection to get rid of the dependency on internal data structures (e.g. InternalRow, or storing DateType as an int32). For example, previously dates were stored as a single integer, but are now stored as java.sql.Date. When we implement the next steps of CBO, we can add code to convert those back into internal types again.
3. Documented clearly what JVM data types are being used to store what data.
4. Defined a simple Map[String, String] interface for serializing and deserializing column stats into/from the catalog.
5. Rearranged the method/function structure so it is more clear what the supported data types are, and also moved how stats are generated into ColumnStat class so they are easy to find.

## How was this patch tested?
Removed most of the original test cases created for column statistics, and added three very simple ones to cover all the cases. The three test cases validate:
1. Roundtrip serialization works.
2. Behavior when analyzing non-existent column or unsupported data type column.
3. Result for stats collection for all valid data types.

Also moved parser related tests into a parser test suite and added an explicit serialization test for the Hive external catalog.

Author: Reynold Xin <rxin@databricks.com>

Closes #15959 from rxin/SPARK-18522.

## What changes were proposed in this pull request?
TaskMemoryManager has a memory leak detector that gets called at task completion callback and checks whether any memory has not been released. If they are not released by the time the callback is invoked, TaskMemoryManager releases them.

The current error message says something like the following:
```
WARN  [Executor task launch worker-0]
org.apache.spark.memory.TaskMemoryManager - leak 16.3 MB memory from
org.apache.spark.unsafe.map.BytesToBytesMap33fb6a15
In practice, there are multiple reasons why these can be triggered in the normal code path (e.g. limit, or task failures), and the fact that these messages are log means the "leak" is fixed by TaskMemoryManager.
```

To not confuse users, this patch downgrade the message from warning to debug level, and avoids using the word "leak" since it is not actually a leak.

## How was this patch tested?
N/A - this is a simple logging improvement.

Author: Reynold Xin <rxin@databricks.com>

Closes #15989 from rxin/SPARK-18557.

## What changes were proposed in this pull request?

In Spark SQL, some expression may output safe format values, e.g. `CreateArray`, `CreateStruct`, `Cast`, etc. When we compare 2 values, we should be able to compare safe and unsafe formats.

The `GreaterThan`, `LessThan`, etc. in Spark SQL already handles it, but the `EqualTo` doesn't. This PR fixes it.

## How was this patch tested?

new unit test and regression test

Author: Wenchen Fan <wenchen@databricks.com>

Closes #15929 from cloud-fan/type-aware.

## What changes were proposed in this pull request?

This would help catch accidental O(n) calls to the hive client as in https://issues.apache.org/jira/browse/SPARK-18507

## How was this patch tested?

Checked that the test fails before https://issues.apache.org/jira/browse/SPARK-18507 was patched. cc cloud-fan

Author: Eric Liang <ekl@databricks.com>

Closes #15985 from ericl/spark-18545.

## What changes were proposed in this pull request?

Updates links to the wiki to links to the new location of content on spark.apache.org.

## How was this patch tested?

Doc builds

Author: Sean Owen <sowen@cloudera.com>

Closes #15967 from srowen/SPARK-18073.1.

[SPARK-18179][SQL] Throws analysis exception with a proper message for unsupported argument types in reflect/java_method function

## What changes were proposed in this pull request?

This PR proposes throwing an `AnalysisException` with a proper message rather than `NoSuchElementException` with the message ` key not found: TimestampType` when unsupported types are given to `reflect` and `java_method` functions.

```scala
spark.range(1).selectExpr("reflect('java.lang.String', 'valueOf', cast('1990-01-01' as timestamp))")
```

produces

**Before**

```
java.util.NoSuchElementException: key not found: TimestampType
  at scala.collection.MapLike$class.default(MapLike.scala:228)
  at scala.collection.AbstractMap.default(Map.scala:59)
  at scala.collection.MapLike$class.apply(MapLike.scala:141)
  at scala.collection.AbstractMap.apply(Map.scala:59)
  at org.apache.spark.sql.catalyst.expressions.CallMethodViaReflection$$anonfun$findMethod$1$$anonfun$apply$1.apply(CallMethodViaReflection.scala:159)
...
```

**After**

```
cannot resolve 'reflect('java.lang.String', 'valueOf', CAST('1990-01-01' AS TIMESTAMP))' due to data type mismatch: arguments from the third require boolean, byte, short, integer, long, float, double or string expressions; line 1 pos 0;
'Project [unresolvedalias(reflect(java.lang.String, valueOf, cast(1990-01-01 as timestamp)), Some(<function1>))]
+- Range (0, 1, step=1, splits=Some(2))
...
```

Added message is,

```
arguments from the third require boolean, byte, short, integer, long, float, double or string expressions
```

## How was this patch tested?

Tests added in `CallMethodViaReflection`.

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #15694 from HyukjinKwon/SPARK-18179.

## What changes were proposed in this pull request?
* Fix SparkR ```spark.glm``` errors when fitting on collinear data, since ```standard error of coefficients, t value and p value``` are not available in this condition.
* Scala/Python GLM summary should throw exception if users get ```standard error of coefficients, t value and p value``` but the underlying WLS was solved by local "l-bfgs".

## How was this patch tested?
Add unit tests.

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #15930 from yanboliang/spark-18501.

## What changes were proposed in this pull request?

Changed Kafka timestamp column type to TimestampType.

## How was this patch tested?

`test("Kafka column types")`.

Author: Shixiong Zhu <shixiong@databricks.com>

Closes #15969 from zsxwing/SPARK-18530.

[SPARK-18533] Raise correct error upon specification of schema for datasource tables created using CTAS

## What changes were proposed in this pull request?
Fixes the inconsistency of error raised between data source and hive serde
tables when schema is specified in CTAS scenario. In the process the grammar for
create table (datasource) is simplified.

**before:**
``` SQL
spark-sql> create table t2 (c1 int, c2 int) using parquet as select * from t1;
Error in query:
mismatched input 'as' expecting {<EOF>, '.', 'OPTIONS', 'CLUSTERED', 'PARTITIONED'}(line 1, pos 64)

== SQL ==
create table t2 (c1 int, c2 int) using parquet as select * from t1
----------------------------------------------------------------^^^
```

**After:**
```SQL
spark-sql> create table t2 (c1 int, c2 int) using parquet as select * from t1
         > ;
Error in query:
Operation not allowed: Schema may not be specified in a Create Table As Select (CTAS) statement(line 1, pos 0)

== SQL ==
create table t2 (c1 int, c2 int) using parquet as select * from t1
^^^
```
## How was this patch tested?
Added a new test in CreateTableAsSelectSuite

Author: Dilip Biswal <dbiswal@us.ibm.com>

Closes #15968 from dilipbiswal/ctas.

### What changes were proposed in this pull request?

In Spark 2.0, `SaveAsTable` does not work when the target table is a Hive serde table, but Spark 1.6 works.

**Spark 1.6**

``` Scala
scala> sql("create table sample.sample stored as SEQUENCEFILE as select 1 as key, 'abc' as value")
res2: org.apache.spark.sql.DataFrame = []

scala> val df = sql("select key, value as value from sample.sample")
df: org.apache.spark.sql.DataFrame = [key: int, value: string]

scala> df.write.mode("append").saveAsTable("sample.sample")

scala> sql("select * from sample.sample").show()
+---+-----+
|key|value|
+---+-----+
|  1|  abc|
|  1|  abc|
+---+-----+
```

**Spark 2.0**

``` Scala
scala> df.write.mode("append").saveAsTable("sample.sample")
org.apache.spark.sql.AnalysisException: Saving data in MetastoreRelation sample, sample
 is not supported.;
```

So far, we do not plan to support it in Spark 2.1 due to the risk. Spark 1.6 works because it internally uses insertInto. But, if we change it back it will break the semantic of saveAsTable (this method uses by-name resolution instead of using by-position resolution used by insertInto). More extra changes are needed to support `hive` as a `format` in DataFrameWriter.

Instead, users should use insertInto API. This PR corrects the error messages. Users can understand how to bypass it before we support it in a separate PR.
### How was this patch tested?

Test cases are added

Author: gatorsmile <gatorsmile@gmail.com>

Closes #15926 from gatorsmile/saveAsTableFix5.

## What changes were proposed in this pull request?

This PR adds `CachedKafkaConsumer.getAndIgnoreLostData` to handle corner cases of `failOnDataLoss=false`.

It also resolves [SPARK-18529](https://issues.apache.org/jira/browse/SPARK-18529) after refactoring codes: Timeout will throw a TimeoutException.

## How was this patch tested?

Because I cannot find any way to manually control the Kafka server to clean up logs, it's impossible to write unit tests for each corner case. Therefore, I just created `test("stress test for failOnDataLoss=false")` which should cover most of corner cases.

I also modified some existing tests to test for both `failOnDataLoss=false` and `failOnDataLoss=true` to make sure it doesn't break existing logic.

Author: Shixiong Zhu <shixiong@databricks.com>

Closes #15820 from zsxwing/failOnDataLoss.

## What changes were proposed in this pull request?

While this behavior is debatable, consider the following use case:
```sql
UNCACHE TABLE foo;
CACHE TABLE foo AS
SELECT * FROM bar
```
The command above fails the first time you run it. But I want to run the command above over and over again, and I don't want to change my code just for the first run of it.
The issue is that subsequent `CACHE TABLE` commands do not overwrite the existing table.

Now we can do:
```sql
UNCACHE TABLE IF EXISTS foo;
CACHE TABLE foo AS
SELECT * FROM bar
```

## How was this patch tested?

Unit tests

Author: Burak Yavuz <brkyvz@gmail.com>

Closes #15896 from brkyvz/uncache.

## What changes were proposed in this pull request?

HiveExternalCatalog.listPartitions should only call `getTable` once, instead of calling it for every partitions.

## How was this patch tested?

N/A

Author: Wenchen Fan <wenchen@databricks.com>

Closes #15978 from cloud-fan/perf.

## What changes were proposed in this pull request?

This PR blocks an incorrect result scenario in scalar subquery where there are GROUP BY column(s)
that are not part of the correlated predicate(s).

Example:
// Incorrect result
Seq(1).toDF("c1").createOrReplaceTempView("t1")
Seq((1,1),(1,2)).toDF("c1","c2").createOrReplaceTempView("t2")
sql("select (select sum(-1) from t2 where t1.c1=t2.c1 group by t2.c2) from t1").show

// How can selecting a scalar subquery from a 1-row table return 2 rows?

## How was this patch tested?
sql/test, catalyst/test
new test case covering the reported problem is added to SubquerySuite.scala

Author: Nattavut Sutyanyong <nsy.can@gmail.com>

Closes #15936 from nsyca/scalarSubqueryIncorrect-1.

## What changes were proposed in this pull request?

Technically map type is not orderable, but can be used in equality comparison. However, due to the limitation of the current implementation, map type can't be used in equality comparison so that it can't be join key or grouping key.

This PR makes this limitation explicit, to avoid wrong result.

## How was this patch tested?

updated tests.

Author: Wenchen Fan <wenchen@databricks.com>

Closes #15956 from cloud-fan/map-type.

[SPARK-18447][DOCS] Fix the markdown for `Note:`/`NOTE:`/`Note that` across Python API documentation

## What changes were proposed in this pull request?

It seems in Python, there are

- `Note:`
- `NOTE:`
- `Note that`
- `.. note::`

This PR proposes to fix those to `.. note::` to be consistent.

**Before**

<img width="567" alt="2016-11-21 1 18 49" src="https://cloud.githubusercontent.com/assets/6477701/20464305/85144c86-af88-11e6-8ee9-90f584dd856c.png">

<img width="617" alt="2016-11-21 12 42 43" src="https://cloud.githubusercontent.com/assets/6477701/20464263/27be5022-af88-11e6-8577-4bbca7cdf36c.png">

**After**

<img width="554" alt="2016-11-21 1 18 42" src="https://cloud.githubusercontent.com/assets/6477701/20464306/8fe48932-af88-11e6-83e1-fc3cbf74407d.png">

<img width="628" alt="2016-11-21 12 42 51" src="https://cloud.githubusercontent.com/assets/6477701/20464264/2d3e156e-af88-11e6-93f3-cab8d8d02983.png">

## How was this patch tested?

The notes were found via

```bash
grep -r "Note: " .
grep -r "NOTE: " .
grep -r "Note that " .
```

And then fixed one by one comparing with API documentation.

After that, manually tested via `make html` under `./python/docs`.

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #15947 from HyukjinKwon/SPARK-18447.

## What changes were proposed in this pull request?

It seems in R, there are

- `Note:`
- `NOTE:`
- `Note that`

This PR proposes to fix those to `Note:` to be consistent.

**Before**

![2016-11-21 11 30 07](https://cloud.githubusercontent.com/assets/6477701/20468848/2f27b0fa-afde-11e6-89e3-993701269dbe.png)

**After**

![2016-11-21 11 29 44](https://cloud.githubusercontent.com/assets/6477701/20468851/39469664-afde-11e6-9929-ad80be7fc405.png)

## How was this patch tested?

The notes were found via

```bash
grep -r "NOTE: " .
grep -r "Note that " .
```

And then fixed one by one comparing with API documentation.

After that, manually tested via `sh create-docs.sh` under `./R`.

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #15952 from HyukjinKwon/SPARK-18514.

## What changes were proposed in this pull request?
When running SparkR job in yarn-cluster mode, it will download Spark package from apache website which is not necessary.
```
./bin/spark-submit --master yarn-cluster ./examples/src/main/r/dataframe.R
```
The following is output:
```
Attaching package: ‘SparkR’

The following objects are masked from ‘package:stats’:

    cov, filter, lag, na.omit, predict, sd, var, window

The following objects are masked from ‘package:base’:

    as.data.frame, colnames, colnames<-, drop, endsWith, intersect,
    rank, rbind, sample, startsWith, subset, summary, transform, union

Spark not found in SPARK_HOME:
Spark not found in the cache directory. Installation will start.
MirrorUrl not provided.
Looking for preferred site from apache website...
......
```
There's no ```SPARK_HOME``` in yarn-cluster mode since the R process is in a remote host of the yarn cluster rather than in the client host. The JVM comes up first and the R process then connects to it. So in such cases we should never have to download Spark as Spark is already running.

## How was this patch tested?
Offline test.

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #15888 from yanboliang/spark-18444.

## What changes were proposed in this pull request?

Right now we are testing the most of `CompactibleFileStreamLog` in `FileStreamSinkLogSuite` (because `FileStreamSinkLog` once was the only subclass of `CompactibleFileStreamLog`, but now it's not the case any more).

Let's refactor the tests so that `CompactibleFileStreamLog` is directly tested, making future changes (like https://github.com/apache/spark/pull/15828, https://github.com/apache/spark/pull/15827) to `CompactibleFileStreamLog` much easier to test and much easier to review.

## How was this patch tested?

the PR itself is about tests

Author: Liwei Lin <lwlin7@gmail.com>

Closes #15870 from lw-lin/test-compact-1113.

## What changes were proposed in this pull request?

This PR adds two of the newly added methods of `Dataset`s to Python:
`withWatermark` and `checkpoint`

## How was this patch tested?

Doc tests

Author: Burak Yavuz <brkyvz@gmail.com>

Closes #15921 from brkyvz/py-watermark.

## What changes were proposed in this pull request?

This PR adds the support for `UserDefinedType` when writing out instead of throwing `ClassCastException` in ORC data source.

In more details, `OrcStruct` is being created based on string from`DataType.catalogString`. For user-defined type, it seems it returns `sqlType.simpleString` for `catalogString` by default[1]. However, during type-dispatching to match the output with the schema, it tries to cast to, for example, `StructType`[2].

So, running the codes below (`MyDenseVector` was borrowed[3]) :

``` scala
val data = Seq((1, new UDT.MyDenseVector(Array(0.25, 2.25, 4.25))))
val udtDF = data.toDF("id", "vectors")
udtDF.write.orc("/tmp/test.orc")
```

ends up throwing an exception as below:

```
java.lang.ClassCastException: org.apache.spark.sql.UDT$MyDenseVectorUDT cannot be cast to org.apache.spark.sql.types.ArrayType
    at org.apache.spark.sql.hive.HiveInspectors$class.wrapperFor(HiveInspectors.scala:381)
    at org.apache.spark.sql.hive.orc.OrcSerializer.wrapperFor(OrcFileFormat.scala:164)
...
```

So, this PR uses `UserDefinedType.sqlType` during finding the correct converter when writing out in ORC data source.

[1]https://github.com/apache/spark/blob/dfdcab00c7b6200c22883baa3ebc5818be09556f/sql/catalyst/src/main/scala/org/apache/spark/sql/types/UserDefinedType.scala#L95
[2]https://github.com/apache/spark/blob/d2dc8c4a162834818190ffd82894522c524ca3e5/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveInspectors.scala#L326
[3]https://github.com/apache/spark/blob/2bfed1a0c5be7d0718fd574a4dad90f4f6b44be7/sql/core/src/test/scala/org/apache/spark/sql/UserDefinedTypeSuite.scala#L38-L70
## How was this patch tested?

Unit tests in `OrcQuerySuite`.

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #15361 from HyukjinKwon/SPARK-17765.

## What changes were proposed in this pull request?

Currently, `DROP TABLE IF EXISTS` shows warning for non-existing tables. However, it had better be quiet for this case by definition of the command.

**BEFORE**
```scala
scala> sql("DROP TABLE IF EXISTS nonexist")
16/11/20 20:48:26 WARN DropTableCommand: org.apache.spark.sql.catalyst.analysis.NoSuchTableException: Table or view 'nonexist' not found in database 'default';
```

**AFTER**
```scala
scala> sql("DROP TABLE IF EXISTS nonexist")
res0: org.apache.spark.sql.DataFrame = []
```

## How was this patch tested?

Manual because this is related to the warning messages instead of exceptions.

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #15953 from dongjoon-hyun/SPARK-18517.

## What changes were proposed in this pull request?

Expose RDD's localCheckpoint() and associated functions in PySpark.

## How was this patch tested?

I added a UnitTest in python/pyspark/tests.py which passes.

I certify that this is my original work, and I license it to the project under the project's open source license.

Gabriel HUANG
Developer at Cardabel (http://cardabel.com/)

Author: Gabriel Huang <gabi.xiaohuang@gmail.com>

Closes #15811 from gabrielhuang/pyspark-localcheckpoint.

## What changes were proposed in this pull request?

This PR adds a new JDBCOption `maxConnections` which means the maximum number of simultaneous JDBC connections allowed. This option applies only to writing with coalesce operation if needed. It defaults to the number of partitions of RDD. Previously, SQL users cannot cannot control this while Scala/Java/Python users can use `coalesce` (or `repartition`) API.

**Reported Scenario**

For the following cases, the number of connections becomes 200 and database cannot handle all of them.

```sql
CREATE OR REPLACE TEMPORARY VIEW resultview
USING org.apache.spark.sql.jdbc
OPTIONS (
  url "jdbc:oracle:thin:10.129.10.111:1521:BKDB",
  dbtable "result",
  user "HIVE",
  password "HIVE"
);
-- set spark.sql.shuffle.partitions=200
INSERT OVERWRITE TABLE resultview SELECT g, count(1) AS COUNT FROM tnet.DT_LIVE_INFO GROUP BY g
```

## How was this patch tested?

Manual. Do the followings and see Spark UI.

**Step 1 (MySQL)**
```
CREATE TABLE t1 (a INT);
CREATE TABLE data (a INT);
INSERT INTO data VALUES (1);
INSERT INTO data VALUES (2);
INSERT INTO data VALUES (3);
```

**Step 2 (Spark)**
```scala
SPARK_HOME=$PWD bin/spark-shell --driver-memory 4G --driver-class-path mysql-connector-java-5.1.40-bin.jar
scala> sql("SET spark.sql.shuffle.partitions=3")
scala> sql("CREATE OR REPLACE TEMPORARY VIEW data USING org.apache.spark.sql.jdbc OPTIONS (url 'jdbc:mysql://localhost:3306/t', dbtable 'data', user 'root', password '')")
scala> sql("CREATE OR REPLACE TEMPORARY VIEW t1 USING org.apache.spark.sql.jdbc OPTIONS (url 'jdbc:mysql://localhost:3306/t', dbtable 't1', user 'root', password '', maxConnections '1')")
scala> sql("INSERT OVERWRITE TABLE t1 SELECT a FROM data GROUP BY a")
scala> sql("CREATE OR REPLACE TEMPORARY VIEW t1 USING org.apache.spark.sql.jdbc OPTIONS (url 'jdbc:mysql://localhost:3306/t', dbtable 't1', user 'root', password '', maxConnections '2')")
scala> sql("INSERT OVERWRITE TABLE t1 SELECT a FROM data GROUP BY a")
scala> sql("CREATE OR REPLACE TEMPORARY VIEW t1 USING org.apache.spark.sql.jdbc OPTIONS (url 'jdbc:mysql://localhost:3306/t', dbtable 't1', user 'root', password '', maxConnections '3')")
scala> sql("INSERT OVERWRITE TABLE t1 SELECT a FROM data GROUP BY a")
scala> sql("CREATE OR REPLACE TEMPORARY VIEW t1 USING org.apache.spark.sql.jdbc OPTIONS (url 'jdbc:mysql://localhost:3306/t', dbtable 't1', user 'root', password '', maxConnections '4')")
scala> sql("INSERT OVERWRITE TABLE t1 SELECT a FROM data GROUP BY a")
```

![maxconnections](https://cloud.githubusercontent.com/assets/9700541/20287987/ed8409c2-aa84-11e6-8aab-ae28e63fe54d.png)

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #15868 from dongjoon-hyun/SPARK-18413.

## What changes were proposed in this pull request?

The nullabilities of `MapObject` can be made more strict by relying on `inputObject.nullable` and `lambdaFunction.nullable`.

Also `ExternalMapToCatalyst.dataType` can be made more strict by relying on `valueConverter.nullable`.

## How was this patch tested?

Existing tests.

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

Closes #15840 from ueshin/issues/SPARK-18398.

## What changes were proposed in this pull request?

Add model summary APIs for `GaussianMixtureModel` and `BisectingKMeansModel` in pyspark.

## How was this patch tested?

Unit tests.

Author: sethah <seth.hendrickson16@gmail.com>

Closes #15777 from sethah/pyspark_cluster_summaries.