KeeProMise commented on code in PR #8072:
URL: https://github.com/apache/hadoop/pull/8072#discussion_r2655406821


##########
hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/RouterClientProtocol.java:
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@@ -1977,8 +1979,68 @@ public BatchedEntries<OpenFileEntry> listOpenFiles(long 
prevId)
   public BatchedEntries<OpenFileEntry> listOpenFiles(long prevId,
       EnumSet<OpenFilesIterator.OpenFilesType> openFilesTypes, String path)
           throws IOException {
-    rpcServer.checkOperation(NameNode.OperationCategory.READ, false);
-    return null;
+    rpcServer.checkOperation(NameNode.OperationCategory.READ, true);
+    List<RemoteLocation> locations = rpcServer.getLocationsForPath(path, 
false, false);
+    RemoteMethod method =
+        new RemoteMethod("listOpenFiles", new Class<?>[] {long.class, 
EnumSet.class, String.class},
+            prevId, openFilesTypes, new RemoteParam());
+    Map<RemoteLocation, BatchedEntries> results =
+        rpcClient.invokeConcurrent(locations, method, true, false, -1, 
BatchedEntries.class);
+
+    // Get the largest inodeIds for each namespace, and the smallest inodeId 
of them
+    // then ignore all entries above this id to keep a consistent prevId for 
the next listOpenFiles
+    long minOfMax = Long.MAX_VALUE;
+    for (BatchedEntries nsEntries : results.values()) {
+      // Only need to care about namespaces that still have more files to 
report
+      if (!nsEntries.hasMore()) {
+        continue;
+      }
+      long max = 0;
+      for (int i = 0; i < nsEntries.size(); i++) {
+        max = Math.max(max, ((OpenFileEntry) nsEntries.get(i)).getId());
+      }
+      minOfMax = Math.min(minOfMax, max);

Review Comment:
   Hi @kokonguyen191  Here's my question: If a router path `testpath` mounts 
two services, `ns1` and `ns2`, with `ns1` having two files and `ns2` having 
five files, then when `routerclient.listOpenFiles(testpath)` is called, does it 
first call `RouterClientProtocol.listOpenFiles(0, ALL_OPEN_FILES, testpath)`, 
returning four files (since `minOfMAX=2`, each `ns` returns two files)? Then, 
because four files are returned, does `routerclientProtocol.listOpenFiles(5, 
ALL_OPEN_FILES, testpath)` only return the fifth file from `ns2`? Would the 
third and fourth files from `ns2` then be missing? I'm unsure if 
`routerclient.listOpenFiles` is called this way internally.



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