[SPARK-17359][SQL][MLLIB] Use ArrayBuffer.+=(A) instead of ArrayBuffer.append(A) in performance critical paths

## What changes were proposed in this pull request?

We should generally use `ArrayBuffer.+=(A)` rather than `ArrayBuffer.append(A)`, because `append(A)` would involve extra boxing / unboxing.

## How was this patch tested?

N/A

Author: Liwei Lin <lwlin7@gmail.com>

Closes #14914 from lw-lin/append_to_plus_eq_v2.

4 files changed, 5 insertions, 6 deletions

diff --git a/core/src/test/scala/org/apache/spark/deploy/IvyTestUtils.scala b/core/src/test/scala/org/apache/spark/deploy/IvyTestUtils.scala
index 9ecf49b598..c9b3d657c2 100644
--- a/core/src/test/scala/org/apache/spark/deploy/IvyTestUtils.scala
+++ b/core/src/test/scala/org/apache/spark/deploy/IvyTestUtils.scala
@@ -305,7 +305,7 @@ private[deploy] object IvyTestUtils {
       val allFiles = ArrayBuffer[(String, File)](javaFile)
       if (withPython) {
         val pythonFile = createPythonFile(root)
-        allFiles.append((pythonFile.getName, pythonFile))
+        allFiles += Tuple2(pythonFile.getName, pythonFile)
       }
       if (withR) {
         val rFiles = createRFiles(root, className, artifact.groupId)
diff --git a/core/src/test/scala/org/apache/spark/memory/MemoryManagerSuite.scala b/core/src/test/scala/org/apache/spark/memory/MemoryManagerSuite.scala
index 38bf7e5e5a..eb2b3ffd15 100644
--- a/core/src/test/scala/org/apache/spark/memory/MemoryManagerSuite.scala
+++ b/core/src/test/scala/org/apache/spark/memory/MemoryManagerSuite.scala
@@ -118,8 +118,7 @@ private[memory] trait MemoryManagerSuite extends SparkFunSuite with BeforeAndAft
         if (numBytesToFree <= mm.storageMemoryUsed) {
           // We can evict enough blocks to fulfill the request for space
           mm.releaseStorageMemory(numBytesToFree, MemoryMode.ON_HEAP)
-          evictedBlocks.append(
-            (null, BlockStatus(StorageLevel.MEMORY_ONLY, numBytesToFree, 0L)))
+          evictedBlocks += Tuple2(null, BlockStatus(StorageLevel.MEMORY_ONLY, numBytesToFree, 0L))
           numBytesToFree
         } else {
           // No blocks were evicted because eviction would not free enough space.
diff --git a/core/src/test/scala/org/apache/spark/shuffle/sort/BypassMergeSortShuffleWriterSuite.scala b/core/src/test/scala/org/apache/spark/shuffle/sort/BypassMergeSortShuffleWriterSuite.scala
index ed9428820f..442941685f 100644
--- a/core/src/test/scala/org/apache/spark/shuffle/sort/BypassMergeSortShuffleWriterSuite.scala
+++ b/core/src/test/scala/org/apache/spark/shuffle/sort/BypassMergeSortShuffleWriterSuite.scala
@@ -107,7 +107,7 @@ class BypassMergeSortShuffleWriterSuite extends SparkFunSuite with BeforeAndAfte
           val blockId = new TempShuffleBlockId(UUID.randomUUID)
           val file = new File(tempDir, blockId.name)
           blockIdToFileMap.put(blockId, file)
-          temporaryFilesCreated.append(file)
+          temporaryFilesCreated += file
           (blockId, file)
         }
       })
diff --git a/core/src/test/scala/org/apache/spark/util/SizeEstimatorSuite.scala b/core/src/test/scala/org/apache/spark/util/SizeEstimatorSuite.scala
index c342b68f46..2695295d45 100644
--- a/core/src/test/scala/org/apache/spark/util/SizeEstimatorSuite.scala
+++ b/core/src/test/scala/org/apache/spark/util/SizeEstimatorSuite.scala
@@ -150,12 +150,12 @@ class SizeEstimatorSuite
 
     val buf = new ArrayBuffer[DummyString]()
     for (i <- 0 until 5000) {
-      buf.append(new DummyString(new Array[Char](10)))
+      buf += new DummyString(new Array[Char](10))
     }
     assertResult(340016)(SizeEstimator.estimate(buf.toArray))
 
     for (i <- 0 until 5000) {
-      buf.append(new DummyString(arr))
+      buf += new DummyString(arr)
     }
     assertResult(683912)(SizeEstimator.estimate(buf.toArray))