[SPARK-14342][CORE][DOCS][TESTS] Remove straggler references to Tachyon

## What changes were proposed in this pull request?

Straggler references to Tachyon were removed:
- for docs, `tachyon` has been generalized as `off-heap memory`;
- for Mesos test suits, the key-value `tachyon:true`/`tachyon:false` has been changed to `os:centos`/`os:ubuntu`, since `os` is an example constrain used by the [Mesos official docs](http://mesos.apache.org/documentation/attributes-resources/).

## How was this patch tested?

Existing test suites.

Author: Liwei Lin <lwlin7@gmail.com>

Closes #12129 from lw-lin/tachyon-cleanup.

3 files changed, 20 insertions, 20 deletions

diff --git a/core/src/main/java/org/apache/spark/api/java/StorageLevels.java b/core/src/main/java/org/apache/spark/api/java/StorageLevels.java
index 666c797738..23673d3e3d 100644
--- a/core/src/main/java/org/apache/spark/api/java/StorageLevels.java
+++ b/core/src/main/java/org/apache/spark/api/java/StorageLevels.java
@@ -39,8 +39,8 @@ public class StorageLevels {
   /**
    * Create a new StorageLevel object.
    * @param useDisk saved to disk, if true
-   * @param useMemory saved to memory, if true
-   * @param useOffHeap saved to Tachyon, if true
+   * @param useMemory saved to on-heap memory, if true
+   * @param useOffHeap saved to off-heap memory, if true
    * @param deserialized saved as deserialized objects, if true
    * @param replication replication factor
    */
diff --git a/core/src/main/scala/org/apache/spark/scheduler/cluster/mesos/MesosSchedulerUtils.scala b/core/src/main/scala/org/apache/spark/scheduler/cluster/mesos/MesosSchedulerUtils.scala
index 35f914355d..233bdc23e6 100644
--- a/core/src/main/scala/org/apache/spark/scheduler/cluster/mesos/MesosSchedulerUtils.scala
+++ b/core/src/main/scala/org/apache/spark/scheduler/cluster/mesos/MesosSchedulerUtils.scala
@@ -283,11 +283,11 @@ private[mesos] trait MesosSchedulerUtils extends Logging {
    *  are separated by ':'. The ':' implies equality (for singular values) and "is one of" for
    *  multiple values (comma separated). For example:
    *  {{{
-   *  parseConstraintString("tachyon:true;zone:us-east-1a,us-east-1b")
+   *  parseConstraintString("os:centos7;zone:us-east-1a,us-east-1b")
    *  // would result in
    *  <code>
    *  Map(
-   *    "tachyon" -> Set("true"),
+   *    "os" -> Set("centos7"),
    *    "zone":   -> Set("us-east-1a", "us-east-1b")
    *  )
    *  }}}
diff --git a/core/src/test/scala/org/apache/spark/scheduler/cluster/mesos/MesosSchedulerUtilsSuite.scala b/core/src/test/scala/org/apache/spark/scheduler/cluster/mesos/MesosSchedulerUtilsSuite.scala
index 85437b2f80..ceb3a52983 100644
--- a/core/src/test/scala/org/apache/spark/scheduler/cluster/mesos/MesosSchedulerUtilsSuite.scala
+++ b/core/src/test/scala/org/apache/spark/scheduler/cluster/mesos/MesosSchedulerUtilsSuite.scala
@@ -59,10 +59,10 @@ class MesosSchedulerUtilsSuite extends SparkFunSuite with Matchers with MockitoS
 
   test("parse a non-empty constraint string correctly") {
     val expectedMap = Map(
-      "tachyon" -> Set("true"),
+      "os" -> Set("centos7"),
       "zone" -> Set("us-east-1a", "us-east-1b")
     )
-    utils.parseConstraintString("tachyon:true;zone:us-east-1a,us-east-1b") should be (expectedMap)
+    utils.parseConstraintString("os:centos7;zone:us-east-1a,us-east-1b") should be (expectedMap)
   }
 
   test("parse an empty constraint string correctly") {
@@ -71,35 +71,35 @@ class MesosSchedulerUtilsSuite extends SparkFunSuite with Matchers with MockitoS
 
   test("throw an exception when the input is malformed") {
     an[IllegalArgumentException] should be thrownBy
-      utils.parseConstraintString("tachyon;zone:us-east")
+      utils.parseConstraintString("os;zone:us-east")
   }
 
   test("empty values for attributes' constraints matches all values") {
-    val constraintsStr = "tachyon:"
+    val constraintsStr = "os:"
     val parsedConstraints = utils.parseConstraintString(constraintsStr)
 
-    parsedConstraints shouldBe Map("tachyon" -> Set())
+    parsedConstraints shouldBe Map("os" -> Set())
 
     val zoneSet = Value.Set.newBuilder().addItem("us-east-1a").addItem("us-east-1b").build()
-    val noTachyonOffer = Map("zone" -> zoneSet)
-    val tachyonTrueOffer = Map("tachyon" -> Value.Text.newBuilder().setValue("true").build())
-    val tachyonFalseOffer = Map("tachyon" -> Value.Text.newBuilder().setValue("false").build())
+    val noOsOffer = Map("zone" -> zoneSet)
+    val centosOffer = Map("os" -> Value.Text.newBuilder().setValue("centos").build())
+    val ubuntuOffer = Map("os" -> Value.Text.newBuilder().setValue("ubuntu").build())
 
-    utils.matchesAttributeRequirements(parsedConstraints, noTachyonOffer) shouldBe false
-    utils.matchesAttributeRequirements(parsedConstraints, tachyonTrueOffer) shouldBe true
-    utils.matchesAttributeRequirements(parsedConstraints, tachyonFalseOffer) shouldBe true
+    utils.matchesAttributeRequirements(parsedConstraints, noOsOffer) shouldBe false
+    utils.matchesAttributeRequirements(parsedConstraints, centosOffer) shouldBe true
+    utils.matchesAttributeRequirements(parsedConstraints, ubuntuOffer) shouldBe true
   }
 
   test("subset match is performed for set attributes") {
     val supersetConstraint = Map(
-      "tachyon" -> Value.Text.newBuilder().setValue("true").build(),
+      "os" -> Value.Text.newBuilder().setValue("ubuntu").build(),
       "zone" -> Value.Set.newBuilder()
         .addItem("us-east-1a")
         .addItem("us-east-1b")
         .addItem("us-east-1c")
         .build())
 
-    val zoneConstraintStr = "tachyon:;zone:us-east-1a,us-east-1c"
+    val zoneConstraintStr = "os:;zone:us-east-1a,us-east-1c"
     val parsedConstraints = utils.parseConstraintString(zoneConstraintStr)
 
     utils.matchesAttributeRequirements(parsedConstraints, supersetConstraint) shouldBe true
@@ -131,10 +131,10 @@ class MesosSchedulerUtilsSuite extends SparkFunSuite with Matchers with MockitoS
   }
 
   test("equality match is performed for text attributes") {
-    val offerAttribs = Map("tachyon" -> Value.Text.newBuilder().setValue("true").build())
+    val offerAttribs = Map("os" -> Value.Text.newBuilder().setValue("centos7").build())
 
-    val trueConstraint = utils.parseConstraintString("tachyon:true")
-    val falseConstraint = utils.parseConstraintString("tachyon:false")
+    val trueConstraint = utils.parseConstraintString("os:centos7")
+    val falseConstraint = utils.parseConstraintString("os:ubuntu")
 
     utils.matchesAttributeRequirements(trueConstraint, offerAttribs) shouldBe true
     utils.matchesAttributeRequirements(falseConstraint, offerAttribs) shouldBe false