[SPARK-1968][SQL] SQL/HiveQL command for caching/uncaching tables

JIRA issue: [SPARK-1968](https://issues.apache.org/jira/browse/SPARK-1968)

This PR added support for SQL/HiveQL command for caching/uncaching tables:

```
scala> sql("CACHE TABLE src")
...
res0: org.apache.spark.sql.SchemaRDD =
SchemaRDD[0] at RDD at SchemaRDD.scala:98
== Query Plan ==
CacheCommandPhysical src, true

scala> table("src")
...
res1: org.apache.spark.sql.SchemaRDD =
SchemaRDD[3] at RDD at SchemaRDD.scala:98
== Query Plan ==
InMemoryColumnarTableScan [key#0,value#1], (HiveTableScan [key#0,value#1], (MetastoreRelation default, src, None), None), false

scala> isCached("src")
res2: Boolean = true

scala> sql("CACHE TABLE src")
...
res3: org.apache.spark.sql.SchemaRDD =
SchemaRDD[4] at RDD at SchemaRDD.scala:98
== Query Plan ==
CacheCommandPhysical src, false

scala> table("src")
...
res4: org.apache.spark.sql.SchemaRDD =
SchemaRDD[11] at RDD at SchemaRDD.scala:98
== Query Plan ==
HiveTableScan [key#2,value#3], (MetastoreRelation default, src, None), None

scala> isCached("src")
res5: Boolean = false
```

Things also work for `hql`.

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

Closes #1038 from liancheng/sqlCacheTable and squashes the following commits:

ecb7194 [Cheng Lian] Trimmed the SQL string before parsing special commands
6f4ce42 [Cheng Lian] Moved logical command classes to a separate file
3458a24 [Cheng Lian] Added comment for public API
f0ffacc [Cheng Lian] Added isCached() predicate
15ec6d2 [Cheng Lian] Added "(UN)CACHE TABLE" SQL/HiveQL statements

(cherry picked from commit 0266a0c8a70e0fbaeb0df63031f7a750ffc31a80)
Signed-off-by: Michael Armbrust <michael@databricks.com>

3 files changed, 70 insertions, 35 deletions

diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/SqlParser.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/SqlParser.scala
index 36758f3114..46fcfbb9e2 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/SqlParser.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/SqlParser.scala
@@ -111,6 +111,7 @@ class SqlParser extends StandardTokenParsers with PackratParsers {
   protected val APPROXIMATE = Keyword("APPROXIMATE")
   protected val AVG = Keyword("AVG")
   protected val BY = Keyword("BY")
+  protected val CACHE = Keyword("CACHE")
   protected val CAST = Keyword("CAST")
   protected val COUNT = Keyword("COUNT")
   protected val DESC = Keyword("DESC")
@@ -149,7 +150,9 @@ class SqlParser extends StandardTokenParsers with PackratParsers {
   protected val SEMI = Keyword("SEMI")
   protected val STRING = Keyword("STRING")
   protected val SUM = Keyword("SUM")
+  protected val TABLE = Keyword("TABLE")
   protected val TRUE = Keyword("TRUE")
+  protected val UNCACHE = Keyword("UNCACHE")
   protected val UNION = Keyword("UNION")
   protected val WHERE = Keyword("WHERE")
 
@@ -189,7 +192,7 @@ class SqlParser extends StandardTokenParsers with PackratParsers {
         UNION ~ ALL ^^^ { (q1: LogicalPlan, q2: LogicalPlan) => Union(q1, q2) } |
         UNION ~ opt(DISTINCT) ^^^ { (q1: LogicalPlan, q2: LogicalPlan) => Distinct(Union(q1, q2)) }
       )
-    | insert
+    | insert | cache
   )
 
   protected lazy val select: Parser[LogicalPlan] =
@@ -220,6 +223,11 @@ class SqlParser extends StandardTokenParsers with PackratParsers {
         InsertIntoTable(r, Map[String, Option[String]](), s, overwrite)
     }
 
+  protected lazy val cache: Parser[LogicalPlan] =
+    (CACHE ^^^ true | UNCACHE ^^^ false) ~ TABLE ~ ident ^^ {
+      case doCache ~ _ ~ tableName => CacheCommand(tableName, doCache)
+    }
+
   protected lazy val projections: Parser[Seq[Expression]] = repsep(projection, ",")
 
   protected lazy val projection: Parser[Expression] =
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/LogicalPlan.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/LogicalPlan.scala
index 7eeb98aea6..0933a31c36 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/LogicalPlan.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/LogicalPlan.scala
@@ -20,7 +20,7 @@ package org.apache.spark.sql.catalyst.plans.logical
 import org.apache.spark.sql.catalyst.errors.TreeNodeException
 import org.apache.spark.sql.catalyst.expressions._
 import org.apache.spark.sql.catalyst.plans.QueryPlan
-import org.apache.spark.sql.catalyst.types.{StringType, StructType}
+import org.apache.spark.sql.catalyst.types.StructType
 import org.apache.spark.sql.catalyst.trees
 
 abstract class LogicalPlan extends QueryPlan[LogicalPlan] {
@@ -97,39 +97,6 @@ abstract class LeafNode extends LogicalPlan with trees.LeafNode[LogicalPlan] {
 }
 
 /**
- * A logical node that represents a non-query command to be executed by the system.  For example,
- * commands can be used by parsers to represent DDL operations.
- */
-abstract class Command extends LeafNode {
-  self: Product =>
-  def output: Seq[Attribute] = Seq.empty  // TODO: SPARK-2081 should fix this
-}
-
-/**
- * Returned for commands supported by a given parser, but not catalyst.  In general these are DDL
- * commands that are passed directly to another system.
- */
-case class NativeCommand(cmd: String) extends Command
-
-/**
- * Commands of the form "SET (key) (= value)".
- */
-case class SetCommand(key: Option[String], value: Option[String]) extends Command {
-  override def output = Seq(
-    AttributeReference("key", StringType, nullable = false)(),
-    AttributeReference("value", StringType, nullable = false)()
-  )
-}
-
-/**
- * Returned by a parser when the users only wants to see what query plan would be executed, without
- * actually performing the execution.
- */
-case class ExplainCommand(plan: LogicalPlan) extends Command {
-  override def output = Seq(AttributeReference("plan", StringType, nullable = false)())
-}
-
-/**
  * A logical plan node with single child.
  */
 abstract class UnaryNode extends LogicalPlan with trees.UnaryNode[LogicalPlan] {
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/commands.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/commands.scala
new file mode 100644
index 0000000000..d05c965275
--- /dev/null
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/commands.scala
@@ -0,0 +1,60 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.catalyst.plans.logical
+
+import org.apache.spark.sql.catalyst.expressions.{AttributeReference, Attribute}
+import org.apache.spark.sql.catalyst.types.StringType
+
+/**
+ * A logical node that represents a non-query command to be executed by the system.  For example,
+ * commands can be used by parsers to represent DDL operations.
+ */
+abstract class Command extends LeafNode {
+  self: Product =>
+  def output: Seq[Attribute] = Seq.empty  // TODO: SPARK-2081 should fix this
+}
+
+/**
+ * Returned for commands supported by a given parser, but not catalyst.  In general these are DDL
+ * commands that are passed directly to another system.
+ */
+case class NativeCommand(cmd: String) extends Command
+
+/**
+ * Commands of the form "SET (key) (= value)".
+ */
+case class SetCommand(key: Option[String], value: Option[String]) extends Command {
+  override def output = Seq(
+    AttributeReference("key", StringType, nullable = false)(),
+    AttributeReference("value", StringType, nullable = false)()
+  )
+}
+
+/**
+ * Returned by a parser when the users only wants to see what query plan would be executed, without
+ * actually performing the execution.
+ */
+case class ExplainCommand(plan: LogicalPlan) extends Command {
+  override def output = Seq(AttributeReference("plan", StringType, nullable = false)())
+}
+
+/**
+ * Returned for the "CACHE TABLE tableName" and "UNCACHE TABLE tableName" command.
+ */
+case class CacheCommand(tableName: String, doCache: Boolean) extends Command
+