[SPARK-23253][Core][Shuffle]Only write shuffle temporary index file when there is not an existing one

core/src/main/scala/org/apache/spark/shuffle/IndexShuffleBlockResolver.scala

@@ -141,19 +141,6 @@ private[spark] class IndexShuffleBlockResolver(
     val indexFile = getIndexFile(shuffleId, mapId)
     val indexTmp = Utils.tempFileWith(indexFile)
     try {
-      val out = new DataOutputStream(new BufferedOutputStream(new FileOutputStream(indexTmp)))
-      Utils.tryWithSafeFinally {
-        // We take in lengths of each block, need to convert it to offsets.
-        var offset = 0L
-        out.writeLong(offset)
-        for (length <- lengths) {
-          offset += length
-          out.writeLong(offset)
-        }
-      } {
-        out.close()
-      }
-
       val dataFile = getDataFile(shuffleId, mapId)
       // There is only one IndexShuffleBlockResolver per executor, this synchronization make sure
       // the following check and rename are atomic.
@@ -166,10 +153,22 @@ private[spark] class IndexShuffleBlockResolver(
           if (dataTmp != null && dataTmp.exists()) {
             dataTmp.delete()
           }
-          indexTmp.delete()
         } else {
           // This is the first successful attempt in writing the map outputs for this task,
           // so override any existing index and data files with the ones we wrote.
+          val out = new DataOutputStream(new BufferedOutputStream(new FileOutputStream(indexTmp)))
+          Utils.tryWithSafeFinally {
+            // We take in lengths of each block, need to convert it to offsets.
+            var offset = 0L
+            out.writeLong(offset)
+            for (length <- lengths) {
+              offset += length
+              out.writeLong(offset)
+            }
+          } {
+            out.close()
+          }
+
           if (indexFile.exists()) {
             indexFile.delete()
           }

core/src/test/scala/org/apache/spark/shuffle/sort/IndexShuffleBlockResolverSuite.scala

@@ -17,7 +17,7 @@
 
 package org.apache.spark.shuffle.sort
 
-import java.io.{File, FileInputStream, FileOutputStream}
+import java.io._
 
 import org.mockito.{Mock, MockitoAnnotations}
 import org.mockito.Answers.RETURNS_SMART_NULLS
@@ -64,6 +64,9 @@ class IndexShuffleBlockResolverSuite extends SparkFunSuite with BeforeAndAfterEa
   }
 
   test("commit shuffle files multiple times") {
+    val shuffleId = 1
+    val mapId = 2
+    val idxName = s"shuffle_${shuffleId}_${mapId}_0.index"
     val resolver = new IndexShuffleBlockResolver(conf, blockManager)
     val lengths = Array[Long](10, 0, 20)
     val dataTmp = File.createTempFile("shuffle", null, tempDir)
@@ -73,9 +76,13 @@ class IndexShuffleBlockResolverSuite extends SparkFunSuite with BeforeAndAfterEa
     } {
       out.close()
     }
-    resolver.writeIndexFileAndCommit(1, 2, lengths, dataTmp)
+    resolver.writeIndexFileAndCommit(shuffleId, mapId, lengths, dataTmp)
 
-    val dataFile = resolver.getDataFile(1, 2)
+    val indexFile = new File(tempDir.getAbsolutePath, idxName)
+    val dataFile = resolver.getDataFile(shuffleId, mapId)
+
+    assert(indexFile.exists())
+    assert(indexFile.length() === (lengths.length + 1) * 8)
     assert(dataFile.exists())
     assert(dataFile.length() === 30)
     assert(!dataTmp.exists())
@@ -89,26 +96,39 @@ class IndexShuffleBlockResolverSuite extends SparkFunSuite with BeforeAndAfterEa
     } {
       out2.close()
     }
-    resolver.writeIndexFileAndCommit(1, 2, lengths2, dataTmp2)
+    resolver.writeIndexFileAndCommit(shuffleId, mapId, lengths2, dataTmp2)
+
+    assert(indexFile.length() === (lengths.length + 1) * 8)
     assert(lengths2.toSeq === lengths.toSeq)
     assert(dataFile.exists())
     assert(dataFile.length() === 30)
     assert(!dataTmp2.exists())
 
     // The dataFile should be the previous one
     val firstByte = new Array[Byte](1)
-    val in = new FileInputStream(dataFile)
+    val dataIn = new FileInputStream(dataFile)
     Utils.tryWithSafeFinally {
-      in.read(firstByte)
+      dataIn.read(firstByte)
     } {
-      in.close()
+      dataIn.close()
     }
     assert(firstByte(0) === 0)
 
+    // The index file should not change
+    val secondBytes = new Array[Byte](8)
+    val indexIn = new FileInputStream(indexFile)
+    Utils.tryWithSafeFinally {
+      indexIn.read(secondBytes)
+      indexIn.read(secondBytes)
+    } {
+      indexIn.close()
+    }
+    assert(secondBytes(7) === 10, "The index file should not change")
+
     // remove data file
     dataFile.delete()
 
-    val lengths3 = Array[Long](10, 10, 15)
+    val lengths3 = Array[Long](7, 10, 15, 3)
     val dataTmp3 = File.createTempFile("shuffle", null, tempDir)
     val out3 = new FileOutputStream(dataTmp3)
     Utils.tryWithSafeFinally {
@@ -117,20 +137,30 @@ class IndexShuffleBlockResolverSuite extends SparkFunSuite with BeforeAndAfterEa
     } {
       out3.close()
     }
-    resolver.writeIndexFileAndCommit(1, 2, lengths3, dataTmp3)
+    resolver.writeIndexFileAndCommit(shuffleId, mapId, lengths3, dataTmp3)
+    assert(indexFile.length() === (lengths3.length + 1) * 8)
     assert(lengths3.toSeq != lengths.toSeq)
     assert(dataFile.exists())
     assert(dataFile.length() === 35)
-    assert(!dataTmp2.exists())
+    assert(!dataTmp3.exists())
 
-    // The dataFile should be the previous one
-    val firstByte2 = new Array[Byte](1)
-    val in2 = new FileInputStream(dataFile)
+    // The dataFile should be the new one, since we deleted the dataFile from the first attempt
+    val dataIn2 = new FileInputStream(dataFile)
+    Utils.tryWithSafeFinally {
+      dataIn2.read(firstByte)
+    } {
+      dataIn2.close()
+    }
+    assert(firstByte(0) === 2)
+
+    // The index file should be updated, since we deleted the dataFile from the first attempt
+    val indexIn2 = new FileInputStream(indexFile)
     Utils.tryWithSafeFinally {
-      in2.read(firstByte2)
+      indexIn2.read(secondBytes)
+      indexIn2.read(secondBytes)
     } {
-      in2.close()
+      indexIn2.close()
     }
-    assert(firstByte2(0) === 2)
+    assert(secondBytes(7) === 7, "The index file should be updated")
   }
 }