attilapiros commented on a change in pull request #29855:
URL: https://github.com/apache/spark/pull/29855#discussion_r500152653



##########
File path: 
common/network-common/src/main/java/org/apache/spark/network/server/TransportRequestHandler.java
##########
@@ -181,6 +182,17 @@ public void onFailure(Throwable e) {
   private void processStreamUpload(final UploadStream req) {
     assert (req.body() == null);
     try {
+      // Retain the original metadata buffer, since it will be used during the 
invocation of
+      // this method. Will be released later.
+      req.meta.retain();
+      // Make a copy of the original metadata buffer. In benchmark, we noticed 
that
+      // we cannot respond the original metadata buffer back to the client, 
otherwise
+      // in cases where multiple concurrent shuffles are present, a wrong 
metadata might
+      // be sent back to client. This is related to the eager release of the 
metadata buffer,
+      // i.e., we always release the original buffer by the time the 
invocation of this
+      // method ends, instead of by the time we respond it to the client. This 
is necessary,
+      // otherwise we start seeing memory issues very quickly in benchmarks.
+      ByteBuffer meta = cloneBuffer(req.meta.nioByteBuffer());

Review comment:
       @otterc 
   https://github.com/apache/spark/pull/29855#discussion_r498985394
   
   > It's cleaner than the current approach.
   
   https://github.com/apache/spark/pull/29855#discussion_r498714105
   
   > This way you can get rid not only the metadata send back but the 
cloneBuffer and JavaUtils.encodeHeaderIntoErrorString and 
BlockPushException#decodeException methods too.
   
   For me `JavaUtils.encodeHeaderIntoErrorString` and 
`BlockPushException#decodeException` is quite painful as they are bit too 
hacky: sending back the meta data within a String along with the the exceptions 
stack. I understand the reason behind. This way such a generic and basic class 
as `RpcFailure` could be kept simple and still reused. But we have a cleaner 
solution at hand. 
   




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