[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.

8 files changed, 13 insertions, 14 deletions

diff --git a/core/src/main/scala/org/apache/spark/api/python/PythonRDD.scala b/core/src/main/scala/org/apache/spark/api/python/PythonRDD.scala
index 2822eb5d60..d841091a31 100644
--- a/core/src/main/scala/org/apache/spark/api/python/PythonRDD.scala
+++ b/core/src/main/scala/org/apache/spark/api/python/PythonRDD.scala
@@ -467,7 +467,7 @@ private[spark] object PythonRDD extends Logging {
           val length = file.readInt()
           val obj = new Array[Byte](length)
           file.readFully(obj)
-          objs.append(obj)
+          objs += obj
         }
       } catch {
         case eof: EOFException => // No-op
diff --git a/core/src/main/scala/org/apache/spark/ui/WebUI.scala b/core/src/main/scala/org/apache/spark/ui/WebUI.scala
index 2c40e72699..38363800ec 100644
--- a/core/src/main/scala/org/apache/spark/ui/WebUI.scala
+++ b/core/src/main/scala/org/apache/spark/ui/WebUI.scala
@@ -83,8 +83,8 @@ private[spark] abstract class WebUI(
       (request: HttpServletRequest) => page.renderJson(request), securityManager, conf, basePath)
     attachHandler(renderHandler)
     attachHandler(renderJsonHandler)
-    pageToHandlers.getOrElseUpdate(page, ArrayBuffer[ServletContextHandler]())
-      .append(renderHandler)
+    val handlers = pageToHandlers.getOrElseUpdate(page, ArrayBuffer[ServletContextHandler]())
+    handlers += renderHandler
   }
 
   /** Attach a handler to this UI. */
diff --git a/core/src/main/scala/org/apache/spark/util/collection/ExternalAppendOnlyMap.scala b/core/src/main/scala/org/apache/spark/util/collection/ExternalAppendOnlyMap.scala
index 0943528119..948cc3b099 100644
--- a/core/src/main/scala/org/apache/spark/util/collection/ExternalAppendOnlyMap.scala
+++ b/core/src/main/scala/org/apache/spark/util/collection/ExternalAppendOnlyMap.scala
@@ -184,7 +184,7 @@ class ExternalAppendOnlyMap[K, V, C](
   override protected[this] def spill(collection: SizeTracker): Unit = {
     val inMemoryIterator = currentMap.destructiveSortedIterator(keyComparator)
     val diskMapIterator = spillMemoryIteratorToDisk(inMemoryIterator)
-    spilledMaps.append(diskMapIterator)
+    spilledMaps += diskMapIterator
   }
 
   /**
@@ -215,7 +215,7 @@ class ExternalAppendOnlyMap[K, V, C](
     // Flush the disk writer's contents to disk, and update relevant variables
     def flush(): Unit = {
       val segment = writer.commitAndGet()
-      batchSizes.append(segment.length)
+      batchSizes += segment.length
       _diskBytesSpilled += segment.length
       objectsWritten = 0
     }
diff --git a/core/src/main/scala/org/apache/spark/util/collection/ExternalSorter.scala b/core/src/main/scala/org/apache/spark/util/collection/ExternalSorter.scala
index 3579918fac..176f84fa2a 100644
--- a/core/src/main/scala/org/apache/spark/util/collection/ExternalSorter.scala
+++ b/core/src/main/scala/org/apache/spark/util/collection/ExternalSorter.scala
@@ -238,7 +238,7 @@ private[spark] class ExternalSorter[K, V, C](
   override protected[this] def spill(collection: WritablePartitionedPairCollection[K, C]): Unit = {
     val inMemoryIterator = collection.destructiveSortedWritablePartitionedIterator(comparator)
     val spillFile = spillMemoryIteratorToDisk(inMemoryIterator)
-    spills.append(spillFile)
+    spills += spillFile
   }
 
   /**
@@ -285,7 +285,7 @@ private[spark] class ExternalSorter[K, V, C](
     // The writer is committed at the end of this process.
     def flush(): Unit = {
       val segment = writer.commitAndGet()
-      batchSizes.append(segment.length)
+      batchSizes += segment.length
       _diskBytesSpilled += segment.length
       objectsWritten = 0
     }
@@ -796,7 +796,7 @@ private[spark] class ExternalSorter[K, V, C](
         logInfo(s"Task ${context.taskAttemptId} force spilling in-memory map to disk and " +
           s" it will release ${org.apache.spark.util.Utils.bytesToString(getUsed())} memory")
         val spillFile = spillMemoryIteratorToDisk(inMemoryIterator)
-        forceSpillFiles.append(spillFile)
+        forceSpillFiles += spillFile
         val spillReader = new SpillReader(spillFile)
         nextUpstream = (0 until numPartitions).iterator.flatMap { p =>
           val iterator = spillReader.readNextPartition()
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))