[SPARK-9458] Avoid object allocation in prefix generation.

In our existing sort prefix generation code, we use expression's eval method to generate the prefix, which results in object allocation for every prefix. We can use the specialized getters available on InternalRow directly to avoid the object allocation.

I also removed the FLOAT prefix, opting for converting float directly to double.

Author: Reynold Xin <rxin@databricks.com>

Closes #7763 from rxin/sort-prefix and squashes the following commits:

5dc2f06 [Reynold Xin] [SPARK-9458] Avoid object allocation in prefix generation.

2 files changed, 0 insertions, 28 deletions

diff --git a/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/PrefixComparators.java b/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/PrefixComparators.java
index bf1bc5dffb..5624e067da 100644
--- a/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/PrefixComparators.java
+++ b/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/PrefixComparators.java
@@ -31,7 +31,6 @@ public class PrefixComparators {
 
   public static final StringPrefixComparator STRING = new StringPrefixComparator();
   public static final IntegralPrefixComparator INTEGRAL = new IntegralPrefixComparator();
-  public static final FloatPrefixComparator FLOAT = new FloatPrefixComparator();
   public static final DoublePrefixComparator DOUBLE = new DoublePrefixComparator();
 
   public static final class StringPrefixComparator extends PrefixComparator {
@@ -78,21 +77,6 @@ public class PrefixComparators {
     public final long NULL_PREFIX = Long.MIN_VALUE;
   }
 
-  public static final class FloatPrefixComparator extends PrefixComparator {
-    @Override
-    public int compare(long aPrefix, long bPrefix) {
-      float a = Float.intBitsToFloat((int) aPrefix);
-      float b = Float.intBitsToFloat((int) bPrefix);
-      return Utils.nanSafeCompareFloats(a, b);
-    }
-
-    public long computePrefix(float value) {
-      return Float.floatToIntBits(value) & 0xffffffffL;
-    }
-
-    public final long NULL_PREFIX = computePrefix(Float.NEGATIVE_INFINITY);
-  }
-
   public static final class DoublePrefixComparator extends PrefixComparator {
     @Override
     public int compare(long aPrefix, long bPrefix) {
diff --git a/core/src/test/scala/org/apache/spark/util/collection/unsafe/sort/PrefixComparatorsSuite.scala b/core/src/test/scala/org/apache/spark/util/collection/unsafe/sort/PrefixComparatorsSuite.scala
index dc03e374b5..28fe925945 100644
--- a/core/src/test/scala/org/apache/spark/util/collection/unsafe/sort/PrefixComparatorsSuite.scala
+++ b/core/src/test/scala/org/apache/spark/util/collection/unsafe/sort/PrefixComparatorsSuite.scala
@@ -48,18 +48,6 @@ class PrefixComparatorsSuite extends SparkFunSuite with PropertyChecks {
     forAll { (s1: String, s2: String) => testPrefixComparison(s1, s2) }
   }
 
-  test("float prefix comparator handles NaN properly") {
-    val nan1: Float = java.lang.Float.intBitsToFloat(0x7f800001)
-    val nan2: Float = java.lang.Float.intBitsToFloat(0x7fffffff)
-    assert(nan1.isNaN)
-    assert(nan2.isNaN)
-    val nan1Prefix = PrefixComparators.FLOAT.computePrefix(nan1)
-    val nan2Prefix = PrefixComparators.FLOAT.computePrefix(nan2)
-    assert(nan1Prefix === nan2Prefix)
-    val floatMaxPrefix = PrefixComparators.FLOAT.computePrefix(Float.MaxValue)
-    assert(PrefixComparators.FLOAT.compare(nan1Prefix, floatMaxPrefix) === 1)
-  }
-
   test("double prefix comparator handles NaNs properly") {
     val nan1: Double = java.lang.Double.longBitsToDouble(0x7ff0000000000001L)
     val nan2: Double = java.lang.Double.longBitsToDouble(0x7fffffffffffffffL)