HDFS-9110. Use Files.walkFileTree in NNUpgradeUtil#doPreUpgrade for better efficiency. Contributed by Charlie Helin.

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -1503,6 +1503,9 @@ Release 2.8.0 - UNRELEASED
     HDFS-9181. Better handling of exceptions thrown during upgrade shutdown.
     (Wei-Chiu Chuang via Yongjun Zhang)
 
+    HDFS-9110. Use Files.walkFileTree in NNUpgradeUtil#doPreUpgrade for
+    better efficiency. (Charlie Helin via wang)
+
   OPTIMIZATIONS
 
     HDFS-8026. Trace FSOutputSummer#writeChecksumChunks rather than

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NNUpgradeUtil.java

@@ -18,10 +18,14 @@
 package org.apache.hadoop.hdfs.server.namenode;
 
 import java.io.File;
-import java.io.FilenameFilter;
 import java.io.IOException;
+import java.nio.file.FileVisitOption;
+import java.nio.file.FileVisitResult;
 import java.nio.file.Files;
-import java.util.List;
+import java.nio.file.Path;
+import java.nio.file.SimpleFileVisitor;
+import java.nio.file.attribute.BasicFileAttributes;
+import java.util.Collections;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -31,7 +35,6 @@ import org.apache.hadoop.hdfs.server.common.Storage.StorageDirectory;
 import org.apache.hadoop.hdfs.server.common.StorageInfo;
 
 import com.google.common.base.Preconditions;
-import org.apache.hadoop.io.IOUtils;
 
 public abstract class NNUpgradeUtil {
   
@@ -116,21 +119,30 @@ public abstract class NNUpgradeUtil {
     // rename current to tmp
     renameCurToTmp(sd);
 
-    final File curDir = sd.getCurrentDir();
-    final File tmpDir = sd.getPreviousTmp();
-    List<String> fileNameList = IOUtils.listDirectory(tmpDir, new FilenameFilter() {
-      @Override
-      public boolean accept(File dir, String name) {
-        return dir.equals(tmpDir)
-            && name.startsWith(NNStorage.NameNodeFile.EDITS.getName());
-      }
-    });
-
-    for (String s : fileNameList) {
-      File prevFile = new File(tmpDir, s);
-      File newFile = new File(curDir, prevFile.getName());
-      Files.createLink(newFile.toPath(), prevFile.toPath());
-    }
+    final Path curDir = sd.getCurrentDir().toPath();
+    final Path tmpDir = sd.getPreviousTmp().toPath();
+
+    Files.walkFileTree(tmpDir,
+      /* do not follow links */ Collections.<FileVisitOption>emptySet(),
+        1, new SimpleFileVisitor<Path>() {
+
+          @Override
+          public FileVisitResult visitFile(Path file, BasicFileAttributes attrs)
+              throws IOException {
+
+            String name = file.getFileName().toString();
+
+            if (Files.isRegularFile(file)
+                && name.startsWith(NNStorage.NameNodeFile.EDITS.getName())) {
+
+              Path newFile = curDir.resolve(name);
+              Files.createLink(newFile, file);
+            }
+
+            return super.visitFile(file, attrs);
+          }
+        }
+    );
   }
 
   /**