Previously, we use 64MB as the default page size, which was way too big for a lot of Spark applications (especially for single node).

This patch changes it so that the default page size, if unset by the user, is determined by the number of cores available and the total execution memory available.

Author: Reynold Xin <rxin@databricks.com>

Closes #8012 from rxin/pagesize and squashes the following commits:

16f4756 [Reynold Xin] Fixed failing test.
5afd570 [Reynold Xin] private...
0d5fb98 [Reynold Xin] Update default value.
674a6cd [Reynold Xin] Address review feedback.
dc00e05 [Reynold Xin] Merge with master.
73ebdb6 [Reynold Xin] [SPARK-9700] Pick default page size more intelligently.

This is a follow-up PR to solve the UI issue when there are multiple SQLContexts. Each SQLContext has a separate tab and contains queries which are executed by this SQLContext.

<img width="1366" alt="multiple sqlcontexts" src="https://cloud.githubusercontent.com/assets/1000778/9088391/54584434-3bc2-11e5-9caf-94c2b0da528e.png">

Author: zsxwing <zsxwing@gmail.com>

Closes #7962 from zsxwing/multi-sqlcontext-ui and squashes the following commits:

cf661e1 [zsxwing] sql -> SQL
39b0c97 [zsxwing] Support multiple SQLContexts in Web UI

Author: Cheng Lian <lian@databricks.com>

Closes #8021 from liancheng/spark-7550/fix-logs and squashes the following commits:

b7bd0ed [Cheng Lian] Fixes logs

Someone may use the Spark core jar in the maven repo with hadoop 1. SPARK-2075 has already resolved the compatibility issue to support it. But `SparkHadoopMapRedUtil.commitTask` broke it recently.

This PR uses Reflection to call `TaskAttemptContext.getTaskAttemptID` to fix the compatibility issue.

Author: zsxwing <zsxwing@gmail.com>

Closes #6599 from zsxwing/SPARK-8057 and squashes the following commits:

f7a343c [zsxwing] Remove the redundant import
6b7f1af [zsxwing] Call TaskAttemptContext.getTaskAttemptID using Reflection

Straightforward fix on doc typo

Author: Jeff Zhang <zjffdu@apache.org>

Closes #8019 from zjffdu/master and squashes the following commits:

aed6e64 [Jeff Zhang] Fix doc typo

spark.sql.tungsten.enabled will be the default value for both codegen and unsafe, they are kept internally for debug/testing.

cc marmbrus rxin

Author: Davies Liu <davies@databricks.com>

Closes #7998 from davies/tungsten and squashes the following commits:

c1c16da [Davies Liu] update doc
1a47be1 [Davies Liu] use tungsten.enabled for both of codegen/unsafe

(cherry picked from commit 4e70e825)
Signed-off-by: Reynold Xin <rxin@databricks.com>

The issue is that a task may run multiple sorts, and the sorts run by the child operator (i.e. parent RDD) may acquire all available memory such that other sorts in the same task do not have enough to proceed. This manifests itself in an `IOException("Unable to acquire X bytes of memory")` thrown by `UnsafeExternalSorter`.

The solution is to reserve a page in each sorter in the chain before computing the child operator's (parent RDD's) partitions. This requires us to use a new special RDD that does some preparation before computing the parent's partitions.

Author: Andrew Or <andrew@databricks.com>

Closes #8011 from andrewor14/unsafe-starve-memory and squashes the following commits:

35b69a4 [Andrew Or] Simplify test
0b07782 [Andrew Or] Minor: update comments
5d5afdf [Andrew Or] Merge branch 'master' of github.com:apache/spark into unsafe-starve-memory
254032e [Andrew Or] Add tests
234acbd [Andrew Or] Reserve a page in sorter when preparing each partition
b889e08 [Andrew Or] MapPartitionsWithPreparationRDD

A small performance optimization – we don't need to generate a Tuple2 and then immediately discard the key. We also don't need an extra wrapper from InterruptibleIterator.

Author: Reynold Xin <rxin@databricks.com>

Closes #8000 from rxin/SPARK-9692 and squashes the following commits:

1d4d0b3 [Reynold Xin] [SPARK-9692] Remove SqlNewHadoopRDD's generated Tuple2 and InterruptibleIterator.

This reverts commit 4e70e825.

Make sure that `$"column"` is consistent with other methods with respect to backticks.  Adds a bunch of tests for various ways of constructing columns.

Author: Michael Armbrust <michael@databricks.com>

Closes #7969 from marmbrus/namesWithDots and squashes the following commits:

53ef3d7 [Michael Armbrust] [SPARK-9650][SQL] Fix quoting behavior on interpolated column names
2bf7a92 [Michael Armbrust] WIP

spark.sql.tungsten.enabled will be the default value for both codegen and unsafe, they are kept internally for debug/testing.

cc marmbrus rxin

Author: Davies Liu <davies@databricks.com>

Closes #7998 from davies/tungsten and squashes the following commits:

c1c16da [Davies Liu] update doc
1a47be1 [Davies Liu] use tungsten.enabled for both of codegen/unsafe

https://issues.apache.org/jira/browse/SPARK-9691

jkbradley rxin

Author: Yin Huai <yhuai@databricks.com>

Closes #7999 from yhuai/pythonRand and squashes the following commits:

4187e0c [Yin Huai] Regression test.
a985ef9 [Yin Huai] Use "if seed is not None" instead "if seed" because "if seed" returns false when seed is 0.

Remove 2 defunct SBT download URLs and replace with the 1 known download URL. Also, use https.
Follow up on https://github.com/apache/spark/pull/7792

Author: Sean Owen <sowen@cloudera.com>

Closes #7956 from srowen/SPARK-9633 and squashes the following commits:

caa40bd [Sean Owen] Remove 2 defunct SBT download URLs and replace with the 1 known download URL. Also, use https.

Spark should not mess with the permissions of directories created
by the cluster manager. Here, by setting the block manager dir
permissions to 700, the shuffle service (running as the YARN user)
wouldn't be able to serve shuffle files created by applications.

Also, the code to protect the local app dir was missing in standalone's
Worker; that has been now added. Since all processes run as the same
user in standalone, `chmod 700` should not cause problems.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #7966 from vanzin/SPARK-9645 and squashes the following commits:

6e07b31 [Marcelo Vanzin] Protect the app dir in standalone mode.
384ba6a [Marcelo Vanzin] [SPARK-9645] [yarn] [core] Allow shuffle service to read shuffle files.

This is the followup of https://github.com/apache/spark/pull/7813. It renames `HybridUnsafeAggregationIterator` to `TungstenAggregationIterator` and makes it only work with `UnsafeRow`. Also, I add a `TungstenAggregate` that uses `TungstenAggregationIterator` and make `SortBasedAggregate` (renamed from `SortBasedAggregate`) only works with `SafeRow`.

Author: Yin Huai <yhuai@databricks.com>

Closes #7954 from yhuai/agg-followUp and squashes the following commits:

4d2f4fc [Yin Huai] Add comments and free map.
0d7ddb9 [Yin Huai] Add TungstenAggregationQueryWithControlledFallbackSuite to test fall back process.
91d69c2 [Yin Huai] Rename UnsafeHybridAggregationIterator to  TungstenAggregateIteraotr and make it only work with UnsafeRow.

Because `JobScheduler.stop(false)` may set `eventLoop` to null when `JobHandler` is running, then it's possible that when `post` is called, `eventLoop` happens to null.

This PR fixed this bug and also set threads in `jobExecutor` to `daemon`.

Author: zsxwing <zsxwing@gmail.com>

Closes #7960 from zsxwing/fix-npe and squashes the following commits:

b0864c4 [zsxwing] Fix a potential NPE in Streaming JobScheduler

…tually visible

Author: cody koeninger <cody@koeninger.org>

Closes #7995 from koeninger/doc-fixes and squashes the following commits:

87af9ea [cody koeninger] [Docs][Streaming] make the existing parameter docs for OffsetRange actually visible

[SPARK-9556] [SPARK-9619] [SPARK-9624] [STREAMING] Make BlockGenerator more robust and make all BlockGenerators subscribe to rate limit updates

In some receivers, instead of using the default `BlockGenerator` in `ReceiverSupervisorImpl`, custom generator with their custom listeners are used for reliability (see [`ReliableKafkaReceiver`](https://github.com/apache/spark/blob/master/external/kafka/src/main/scala/org/apache/spark/streaming/kafka/ReliableKafkaReceiver.scala#L99) and [updated `KinesisReceiver`](https://github.com/apache/spark/pull/7825/files)). These custom generators do not receive rate updates. This PR modifies the code to allow custom `BlockGenerator`s to be created through the `ReceiverSupervisorImpl` so that they can be kept track and rate updates can be applied.

In the process, I did some simplification, and de-flaki-fication of some rate controller related tests. In particular.
- Renamed `Receiver.executor` to `Receiver.supervisor` (to match `ReceiverSupervisor`)
- Made `RateControllerSuite` faster (by increasing batch interval) and less flaky
- Changed a few internal API to return the current rate of block generators as Long instead of Option\[Long\] (was inconsistent at places).
- Updated existing `ReceiverTrackerSuite` to test that custom block generators get rate updates as well.

Author: Tathagata Das <tathagata.das1565@gmail.com>

Closes #7913 from tdas/SPARK-9556 and squashes the following commits:

41d4461 [Tathagata Das] fix scala style
eb9fd59 [Tathagata Das] Updated kinesis receiver
d24994d [Tathagata Das] Updated BlockGeneratorSuite to use manual clock in BlockGenerator
d70608b [Tathagata Das] Updated BlockGenerator with states and proper synchronization
f6bd47e [Tathagata Das] Merge remote-tracking branch 'apache-github/master' into SPARK-9556
31da173 [Tathagata Das] Fix bug
12116df [Tathagata Das] Add BlockGeneratorSuite
74bd069 [Tathagata Das] Fix style
989bb5c [Tathagata Das] Made BlockGenerator fail is used after stop, and added better unit tests for it
3ff618c [Tathagata Das] Fix test
b40eff8 [Tathagata Das] slight refactoring
f0df0f1 [Tathagata Das] Scala style fixes
51759cb [Tathagata Das] Refactored rate controller tests and added the ability to update rate of any custom block generator

This pull request adds a destructive iterator to BytesToBytesMap. When used, the iterator frees pages as it traverses them. This is part of the effort to avoid starving when we have more than one operators that can exhaust memory.

This is based on #7924, but fixes a bug there (Don't use destructive iterator in UnsafeKVExternalSorter).

Closes #7924.

Author: Liang-Chi Hsieh <viirya@appier.com>
Author: Reynold Xin <rxin@databricks.com>

Closes #8003 from rxin/map-destructive-iterator and squashes the following commits:

6b618c3 [Reynold Xin] Don't use destructive iterator in UnsafeKVExternalSorter.
a7bd8ec [Reynold Xin] Merge remote-tracking branch 'viirya/destructive_iter' into map-destructive-iterator
7652083 [Liang-Chi Hsieh] For comments: add destructiveIterator(), modify unit test, remove code block.
4a3e9de [Liang-Chi Hsieh] Merge remote-tracking branch 'upstream/master' into destructive_iter
581e9e3 [Liang-Chi Hsieh] Merge remote-tracking branch 'upstream/master' into destructive_iter
f0ff783 [Liang-Chi Hsieh] No need to free last page.
9e9d2a3 [Liang-Chi Hsieh] Add a destructive iterator for BytesToBytesMap.

The golden answer file names for the existing Hive comparison tests were generated using a MD5 hash of the query text which uses Unix-style line separator characters `\n` (LF).
This PR ensures that all occurrences of the Windows-style line separator `\r\n` (CR) are replaced with `\n` (LF) before generating the MD5 hash to produce an identical MD5 hash for golden answer file names generated on Windows.

Author: Christian Kadner <ckadner@us.ibm.com>

Closes #7563 from ckadner/SPARK-9211_working and squashes the following commits:

d541db0 [Christian Kadner] [SPARK-9211][SQL] normalize line separators before MD5 hash

This PR contains the following changes:
* add `featureIndex` to handle vector features (in order to chain isotonic regression easily with output from logistic regression
* make getter/setter names consistent with params
* remove inheritance from Regressor because it is tricky to handle both `DoubleType` and `VectorType`
* simplify test data generation

jkbradley zapletal-martin

Author: Xiangrui Meng <meng@databricks.com>

Closes #7952 from mengxr/SPARK-9493 and squashes the following commits:

8818ac3 [Xiangrui Meng] address comments
05e2216 [Xiangrui Meng] address comments
8d08090 [Xiangrui Meng] add featureIndex to handle vector features make getter/setter names consistent with params remove inheritance from Regressor

This re-applies #7955, which was reverted due to a race condition to fix build breaking.

Author: Wenchen Fan <cloud0fan@outlook.com>
Author: Reynold Xin <rxin@databricks.com>

Closes #8002 from rxin/InternalRow-toSeq and squashes the following commits:

332416a [Reynold Xin] Merge pull request #7955 from cloud-fan/toSeq
21665e2 [Wenchen Fan] fix hive again...
4addf29 [Wenchen Fan] fix hive
bc16c59 [Wenchen Fan] minor fix
33d802c [Wenchen Fan] pass data type info to InternalRow.toSeq
3dd033e [Wenchen Fan] move the default special getters implementation from InternalRow to BaseGenericInternalRow

Author: Dean Wampler <dean@concurrentthought.com>
Author: Nilanjan Raychaudhuri <nraychaudhuri@gmail.com>
Author: François Garillot <francois@garillot.net>

Closes #7796 from dragos/topic/streaming-bp/kafka-direct and squashes the following commits:

50d1f21 [Nilanjan Raychaudhuri] Taking care of the remaining nits
648c8b1 [Dean Wampler] Refactored rate controller test to be more predictable and run faster.
e43f678 [Nilanjan Raychaudhuri] fixing doc and nits
ce19d2a [Dean Wampler] Removing an unreliable assertion.
9615320 [Dean Wampler] Give me a break...
6372478 [Dean Wampler] Found a few ways to make this test more robust...
9e69e37 [Dean Wampler] Attempt to fix flakey test that fails in CI, but not locally :(
d3db1ea [Dean Wampler] Fixing stylecheck errors.
d04a288 [Nilanjan Raychaudhuri] adding test to make sure rate controller is used to calculate maxMessagesPerPartition
b6ecb67 [Nilanjan Raychaudhuri] Fixed styling issue
3110267 [Nilanjan Raychaudhuri] [SPARK-8978][Streaming] Implements the DirectKafkaRateController
393c580 [François Garillot] [SPARK-8978][Streaming] Implements the DirectKafkaRateController
51e78c6 [Nilanjan Raychaudhuri] Rename and fix build failure
2795509 [Nilanjan Raychaudhuri] Added missing RateController
19200f5 [Dean Wampler] Removed usage of infix notation. Changed a private variable name to be more consistent with usage.
aa4a70b [François Garillot] [SPARK-8978][Streaming] Implements the DirectKafkaController

Document spark.shuffle.service.{enabled,port}

CC sryza tgravescs
This is pretty minimal; is there more to say here about the service?

Author: Sean Owen <sowen@cloudera.com>

Closes #7991 from srowen/SPARK-9641 and squashes the following commits:

3bb946e [Sean Owen] Add link to docs for setup and config of external shuffle service
2302e01 [Sean Owen] Document spark.shuffle.service.{enabled,port}

seems https://github.com/apache/spark/pull/7955 breaks the build.

Author: Yin Huai <yhuai@databricks.com>

Closes #8001 from yhuai/SPARK-9632-fixBuild and squashes the following commits:

6c257dd [Yin Huai] Fix build.

This reverts commit 6e009cb9.

Author: Wenchen Fan <cloud0fan@outlook.com>

Closes #7955 from cloud-fan/toSeq and squashes the following commits:

21665e2 [Wenchen Fan] fix hive again...
4addf29 [Wenchen Fan] fix hive
bc16c59 [Wenchen Fan] minor fix
33d802c [Wenchen Fan] pass data type info to InternalRow.toSeq
3dd033e [Wenchen Fan] move the default special getters implementation from InternalRow to BaseGenericInternalRow

Inspiration drawn from this blog post: https://lab.getbase.com/pandarize-spark-dataframes/

Author: Reynold Xin <rxin@databricks.com>

Closes #7977 from rxin/isin and squashes the following commits:

9b1d3d6 [Reynold Xin] Added return.
2197d37 [Reynold Xin] Fixed test case.
7c1b6cf [Reynold Xin] Import warnings.
4f4a35d [Reynold Xin] [SPARK-9659][SQL] Rename inSet to isin to match Pandas function.

[SPARK-9615] [SPARK-9616] [SQL] [MLLIB] Bugs related to FrequentItems when merging and with Tungsten

In short:
1- FrequentItems should not use the InternalRow representation, because the keys in the map get messed up. For example, every key in the Map correspond to the very last element observed in the partition, when the elements are strings.

2- Merging two partitions had a bug:

**Existing behavior with size 3**
Partition A -> Map(1 -> 3, 2 -> 3, 3 -> 4)
Partition B -> Map(4 -> 25)
Result -> Map()

**Correct Behavior:**
Partition A -> Map(1 -> 3, 2 -> 3, 3 -> 4)
Partition B -> Map(4 -> 25)
Result -> Map(3 -> 1, 4 -> 22)

cc mengxr rxin JoshRosen

Author: Burak Yavuz <brkyvz@gmail.com>

Closes #7945 from brkyvz/freq-fix and squashes the following commits:

07fa001 [Burak Yavuz] address 2
1dc61a8 [Burak Yavuz] address 1
506753e [Burak Yavuz] fixed and added reg test
47bfd50 [Burak Yavuz] pushing

After https://github.com/apache/spark/pull/7263 it is pretty straightforward to Python wrappers.

Author: MechCoder <manojkumarsivaraj334@gmail.com>

Closes #7930 from MechCoder/spark-9533 and squashes the following commits:

1bea394 [MechCoder] make getVectors a lazy val
5522756 [MechCoder] [SPARK-9533] [PySpark] [ML] Add missing methods in Word2Vec ML

I have added support for stats in LogisticRegression. The API is similar to that of LinearRegression with LogisticRegressionTrainingSummary and LogisticRegressionSummary

I have some queries and asked them inline.

Author: MechCoder <manojkumarsivaraj334@gmail.com>

Closes #7538 from MechCoder/log_reg_stats and squashes the following commits:

2e9f7c7 [MechCoder] Change defs into lazy vals
d775371 [MechCoder] Clean up class inheritance
9586125 [MechCoder] Add abstraction to handle Multiclass Metrics
40ad8ef [MechCoder] minor
640376a [MechCoder] remove unnecessary dataframe stuff and add docs
80d9954 [MechCoder] Added tests
fbed861 [MechCoder] DataFrame support for metrics
70a0fc4 [MechCoder] [SPARK-9112] [ML] Implement Stats for LogisticRegression

This is a follow-up of #7929.

We found that Jenkins SBT master build still fails because of the Hadoop shims loading issue. But the failure doesn't appear to be deterministic. My suspect is that Hadoop `VersionInfo` class may fail to inspect Hadoop version, and the shims loading branch is skipped.

This PR tries to make the fix more robust:

1. When Hadoop version is available, we load `Hadoop20SShims` for versions <= 2.0.x as srowen suggested in PR #7929.
2. Otherwise, we use `Path.getPathWithoutSchemeAndAuthority` as a probe method, which doesn't exist in Hadoop 1.x or 2.0.x. If this method is not found, `Hadoop20SShims` is also loaded.

Author: Cheng Lian <lian@databricks.com>

Closes #7994 from liancheng/spark-9593/fix-hadoop-shims and squashes the following commits:

e1d3d70 [Cheng Lian] Fixes typo in comments
8d971da [Cheng Lian] Makes the Hadoop shims loading fix more robust

This PR also change to use `def` instead of `lazy val` for UnsafeProjection, because it's not thread safe.

TODO: cleanup the debug code once the flaky test passed 100 times.

Author: Davies Liu <davies@databricks.com>

Closes #7940 from davies/semijoin and squashes the following commits:

93baac7 [Davies Liu] fix outerjoin
5c40ded [Davies Liu] address comments
aa3de46 [Davies Liu] Merge branch 'master' of github.com:apache/spark into semijoin
7590a25 [Davies Liu] Merge branch 'master' of github.com:apache/spark into semijoin
2d4085b [Davies Liu] use def for resultProjection
0833407 [Davies Liu] Merge branch 'semijoin' of github.com:davies/spark into semijoin
e0d8c71 [Davies Liu] use lazy val
6a59e8f [Davies Liu] Update HashedRelation.scala
0fdacaf [Davies Liu] fix broadcast and thread-safety of UnsafeProjection
2fc3ef6 [Davies Liu] reproduce failure in semijoin

In order to support update a varlength (actually fixed length) object, the space should be preserved even  it's null. And, we can't call setNullAt(i) for it anymore, we because setNullAt(i) will remove the offset of the preserved space, should call setDecimal(i, null, precision) instead.

After this, we can do hash based aggregation on DecimalType with precision > 18. In a tests, this could decrease the end-to-end run time of aggregation query from 37 seconds (sort based) to 24 seconds (hash based).

cc rxin

Author: Davies Liu <davies@databricks.com>

Closes #7978 from davies/update_decimal and squashes the following commits:

bed8100 [Davies Liu] isSettable -> isMutable
923c9eb [Davies Liu] address comments and fix bug
385891d [Davies Liu] Merge branch 'master' of github.com:apache/spark into update_decimal
36a1872 [Davies Liu] fix tests
cd6c524 [Davies Liu] support set decimal with precision > 18

![translate](http://www.w3resource.com/PostgreSQL/postgresql-translate-function.png)

Author: zhichao.li <zhichao.li@intel.com>

Closes #7709 from zhichao-li/translate and squashes the following commits:

9418088 [zhichao.li] refine checking condition
f2ab77a [zhichao.li] clone string
9d88f2d [zhichao.li] fix indent
6aa2962 [zhichao.li] style
e575ead [zhichao.li] add python api
9d4bab0 [zhichao.li] add special case for fodable and refactor unittest
eda7ad6 [zhichao.li] update to use TernaryExpression
cdfd4be [zhichao.li] add function translate

https://issues.apache.org/jira/browse/SPARK-9664

Author: Yin Huai <yhuai@databricks.com>

Closes #7982 from yhuai/udafRegister and squashes the following commits:

0cc2287 [Yin Huai] Remove UDAFRegistration and add apply to UserDefinedAggregateFunction.

The new aggregate replaces the old GeneratedAggregate.

Author: Reynold Xin <rxin@databricks.com>

Closes #7983 from rxin/remove-generated-agg and squashes the following commits:

8334aae [Reynold Xin] [SPARK-9674][SQL] Remove GeneratedAggregate.

[SPARK-6923] [SPARK-7550] [SQL] Persists data source relations in Hive compatible format when possible

This PR is a fork of PR #5733 authored by chenghao-intel.  For committers who's going to merge this PR, please set the author to "Cheng Hao <hao.chengintel.com>".

----

When a data source relation meets the following requirements, we persist it in Hive compatible format, so that other systems like Hive can access it:

1. It's a `HadoopFsRelation`
2. It has only one input path
3. It's non-partitioned
4. It's data source provider can be naturally mapped to a Hive builtin SerDe (e.g. ORC and Parquet)

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

Closes #7967 from liancheng/spark-6923/refactoring-pr-5733 and squashes the following commits:

5175ee6 [Cheng Lian] Fixes an oudated comment
3870166 [Cheng Lian] Fixes build error and comments
864acee [Cheng Lian] Refactors PR #5733
3490cdc [Cheng Hao] update the scaladoc
6f57669 [Cheng Hao] write schema info to hivemetastore for data source

This PR has the following three small fixes.

1. UnsafeKVExternalSorter does not use 0 as the initialSize to create an UnsafeInMemorySorter if its BytesToBytesMap is empty.
2. We will not not spill a InMemorySorter if it is empty.
3. We will not add a SpillReader to a SpillMerger if this SpillReader is empty.

JIRA: https://issues.apache.org/jira/browse/SPARK-9611

Author: Yin Huai <yhuai@databricks.com>

Closes #7948 from yhuai/unsafeEmptyMap and squashes the following commits:

9727abe [Yin Huai] Address Josh's comments.
34b6f76 [Yin Huai] 1. UnsafeKVExternalSorter does not use 0 as the initialSize to create an UnsafeInMemorySorter if its BytesToBytesMap is empty. 2. Do not spill a InMemorySorter if it is empty. 3. Do not add spill to SpillMerger if this spill is empty.

First, it's probably a bad idea to call generated Scala methods
from Java. In this case, the method being called wasn't actually
"Utils.createTempDir()", but actually the method that returns the
first default argument to the actual createTempDir method, which
is just the location of java.io.tmpdir; meaning that all tests in
the class were using the same temp dir, and thus affecting each
other.

Second, spillingOccursInResponseToMemoryPressure was not writing
enough records to actually cause a spill.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #7970 from vanzin/SPARK-9651 and squashes the following commits:

74d357f [Marcelo Vanzin] Clean up temp dir on test tear down.
a64f36a [Marcelo Vanzin] [SPARK-9651] Fix UnsafeExternalSorterSuite.