HDFS-13227. Add a method to calculate cumulative diff over multiple snapshots in DirectoryDiffList. Contributed by Shashikant Banerjee

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

@@ -235,6 +235,12 @@ abstract class AbstractINodeDiffList<N extends INode,
     return diff == null ? Snapshot.CURRENT_STATE_ID : diff.getSnapshotId();
   }
 
+  public final int getDiffIndexById(final int snapshotId) {
+    int diffIndex = diffs.binarySearch(snapshotId);
+    diffIndex = diffIndex < 0 ? (-diffIndex - 1) : diffIndex;
+    return diffIndex;
+  }
+
   final int[] changedBetweenSnapshots(Snapshot from, Snapshot to) {
     if (diffs == null) {
       return null;
@@ -247,10 +253,10 @@ abstract class AbstractINodeDiffList<N extends INode,
     }
 
     final int size = diffs.size();
-    int earlierDiffIndex = diffs.binarySearch(earlier.getId());
+    int earlierDiffIndex = getDiffIndexById(earlier.getId());
     int laterDiffIndex = later == null ? size
-        : diffs.binarySearch(later.getId());
-    if (-earlierDiffIndex - 1 == size) {
+        : getDiffIndexById(later.getId());
+    if (earlierDiffIndex == size) {
       // if the earlierSnapshot is after the latest SnapshotDiff stored in
       // diffs, no modification happened after the earlierSnapshot
       return null;
@@ -260,10 +266,6 @@ abstract class AbstractINodeDiffList<N extends INode,
       // before it, no modification happened before the laterSnapshot
       return null;
     }
-    earlierDiffIndex = earlierDiffIndex < 0 ? (-earlierDiffIndex - 1)
-        : earlierDiffIndex;
-    laterDiffIndex = laterDiffIndex < 0 ? (-laterDiffIndex - 1)
-        : laterDiffIndex;
     return new int[]{earlierDiffIndex, laterDiffIndex};
   }
 
@@ -304,7 +306,7 @@ abstract class AbstractINodeDiffList<N extends INode,
     }
     return diff;
   }
-  
+
   @Override
   public Iterator<D> iterator() {
     return diffs != null ? diffs.iterator() : Collections.emptyIterator();

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

@@ -228,12 +228,18 @@ public class DirectoryWithSnapshotFeature implements INode.Feature {
         private List<INode> initChildren() {
           if (children == null) {
             final ChildrenDiff combined = new ChildrenDiff();
-            for (DirectoryDiff d = DirectoryDiff.this; d != null;
-                d = d.getPosterior()) {
+            DirectoryDiffList directoryDiffList =
+                currentDir.getDirectoryWithSnapshotFeature().diffs;
+            final int diffIndex =
+                directoryDiffList.getDiffIndexById(getSnapshotId());
+            List<DirectoryDiff> diffList = directoryDiffList
+                .getDiffListBetweenSnapshots(diffIndex,
+                    directoryDiffList.asList().size(), currentDir);
+            for (DirectoryDiff d : diffList) {
               combined.combinePosterior(d.diff, null);
             }
-            children = combined.apply2Current(ReadOnlyList.Util.asList(
-                currentDir.getChildrenList(Snapshot.CURRENT_STATE_ID)));
+            children = combined.apply2Current(ReadOnlyList.Util
+                .asList(currentDir.getChildrenList(Snapshot.CURRENT_STATE_ID)));
           }
           return children;
         }
@@ -383,6 +389,19 @@ public class DirectoryWithSnapshotFeature implements INode.Feature {
       }
       return NO_SNAPSHOT_ID;
     }
+
+    /**
+     * Returns the list of diffs between two indexes corresponding to two
+     * snapshots.
+     * @param fromIndex Index of the diff corresponding to the earlier snapshot
+     * @param toIndex   Index of the diff corresponding to the later snapshot
+     * @param dir       The Directory to which the diffList belongs
+     * @return list of directory diffs
+     */
+    List<DirectoryDiff> getDiffListBetweenSnapshots(int fromIndex, int toIndex,
+        INodeDirectory dir) {
+      return asList().getMinListForRange(fromIndex, toIndex, dir);
+    }
   }
   
   private static Map<INode, INode> cloneDiffList(List<INode> diffList) {
@@ -597,7 +616,7 @@ public class DirectoryWithSnapshotFeature implements INode.Feature {
     return diff != null ? diff.getChild(name, true, currentINode)
         : currentINode.getChild(name, Snapshot.CURRENT_STATE_ID);
   }
-  
+
   /** Used to record the modification of a symlink node */
   public INode saveChild2Snapshot(INodeDirectory currentINode,
       final INode child, final int latestSnapshotId, final INode snapshotCopy) {
@@ -678,9 +697,10 @@ public class DirectoryWithSnapshotFeature implements INode.Feature {
 
     boolean dirMetadataChanged = false;
     INodeDirectoryAttributes dirCopy = null;
-    DiffList<DirectoryDiff> difflist = diffs.asList();
-    for (int i = earlierDiffIndex; i < laterDiffIndex; i++) {
-      DirectoryDiff sdiff = difflist.get(i);
+    List<DirectoryDiff> difflist = diffs
+        .getDiffListBetweenSnapshots(earlierDiffIndex, laterDiffIndex,
+            currentINode);
+    for (DirectoryDiff sdiff : difflist) {
       diff.combinePosterior(sdiff.diff, null);
       if (!dirMetadataChanged && sdiff.snapshotINode != null) {
         if (dirCopy == null) {