LiuGuH commented on code in PR #6784:
URL: https://github.com/apache/hadoop/pull/6784#discussion_r1595269674


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hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/RouterClientProtocol.java:
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@@ -667,39 +667,28 @@ public void rename2(final String src, final String dst,
   public void concat(String trg, String[] src) throws IOException {
     rpcServer.checkOperation(NameNode.OperationCategory.WRITE);
 
-    // See if the src and target files are all in the same namespace
-    LocatedBlocks targetBlocks = getBlockLocations(trg, 0, 1);
-    if (targetBlocks == null) {
-      throw new IOException("Cannot locate blocks for target file - " + trg);
-    }
-    LocatedBlock lastLocatedBlock = targetBlocks.getLastLocatedBlock();
-    String targetBlockPoolId = lastLocatedBlock.getBlock().getBlockPoolId();
-    for (String source : src) {
-      LocatedBlocks sourceBlocks = getBlockLocations(source, 0, 1);
-      if (sourceBlocks == null) {
-        throw new IOException(
-            "Cannot located blocks for source file " + source);
-      }
-      String sourceBlockPoolId =
-          sourceBlocks.getLastLocatedBlock().getBlock().getBlockPoolId();
-      if (!sourceBlockPoolId.equals(targetBlockPoolId)) {
-        throw new IOException("Cannot concatenate source file " + source
-            + " because it is located in a different namespace"
-            + " with block pool id " + sourceBlockPoolId
-            + " from the target file with block pool id "
-            + targetBlockPoolId);
-      }
-    }
+    // Concat only effects when all files in same namespace.
+    // And in router view, a file only exists in one RemoteLocation.

Review Comment:
   Thanks for review.
   
   > you can refer to this case:
   > 
   > * /path mounts to NS1, NS2 and NS3
   > * NS2 and NS3 contains /path
   > * `OrderedResolver` returns NS1, NS2 and NS3
   > 
   > for this case, we should proxy this `concat` to NS2 instead of NS1, right?
   
   This only happens when /path is a directory. And for a file ,it must only be 
from one exactly nameservice via dfsrouter.
   
   



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