HDFS-6690. Deduplicate xattr names in memory. (wang)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1611226 13f79535-47bb-0310-9956-ffa450edef68

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

@@ -294,6 +294,8 @@ Release 2.6.0 - UNRELEASED
 
   OPTIMIZATIONS
 
+    HDFS-6690. Deduplicate xattr names in memory. (wang)
+
   BUG FIXES
 
     HDFS-6617. Flake TestDFSZKFailoverController.testManualFailoverWithDFSHAAdmin

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

@@ -19,24 +19,30 @@
 package org.apache.hadoop.hdfs.server.namenode;
 
 import java.util.List;
+import java.util.Map;
 
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.Lists;
+import com.google.common.collect.Maps;
 import org.apache.hadoop.classification.InterfaceAudience;
 import org.apache.hadoop.fs.XAttr;
 import org.apache.hadoop.hdfs.protocol.QuotaExceededException;
-import org.apache.hadoop.hdfs.server.namenode.INode;
-
-import com.google.common.collect.ImmutableList;
 
 /**
  * XAttrStorage is used to read and set xattrs for an inode.
  */
 @InterfaceAudience.Private
 public class XAttrStorage {
-  
+
+  private static final Map<String, String> internedNames = Maps.newHashMap();
+
   /**
    * Reads the existing extended attributes of an inode. If the 
    * inode does not have an <code>XAttr</code>, then this method
    * returns an empty list.
+   * <p/>
+   * Must be called while holding the FSDirectory read lock.
+   *
    * @param inode INode to read
    * @param snapshotId
    * @return List<XAttr> <code>XAttr</code> list. 
@@ -48,6 +54,9 @@ public class XAttrStorage {
   
   /**
    * Reads the existing extended attributes of an inode.
+   * <p/>
+   * Must be called while holding the FSDirectory read lock.
+   *
    * @param inode INode to read.
    * @return List<XAttr> <code>XAttr</code> list.
    */
@@ -58,6 +67,9 @@ public class XAttrStorage {
   
   /**
    * Update xattrs of inode.
+   * <p/>
+   * Must be called while holding the FSDirectory write lock.
+   * 
    * @param inode INode to update
    * @param xAttrs to update xAttrs.
    * @param snapshotId id of the latest snapshot of the inode
@@ -70,8 +82,24 @@ public class XAttrStorage {
       }
       return;
     }
-    
-    ImmutableList<XAttr> newXAttrs = ImmutableList.copyOf(xAttrs);
+    // Dedupe the xAttr name and save them into a new interned list
+    List<XAttr> internedXAttrs = Lists.newArrayListWithCapacity(xAttrs.size());
+    for (XAttr xAttr : xAttrs) {
+      final String name = xAttr.getName();
+      String internedName = internedNames.get(name);
+      if (internedName == null) {
+        internedName = name;
+        internedNames.put(internedName, internedName);
+      }
+      XAttr internedXAttr = new XAttr.Builder()
+          .setName(internedName)
+          .setNameSpace(xAttr.getNameSpace())
+          .setValue(xAttr.getValue())
+          .build();
+      internedXAttrs.add(internedXAttr);
+    }
+    // Save the list of interned xattrs
+    ImmutableList<XAttr> newXAttrs = ImmutableList.copyOf(internedXAttrs);
     if (inode.getXAttrFeature() != null) {
       inode.removeXAttrFeature(snapshotId);
     }