[GitHub] [spark] otterc commented on a change in pull request #29855: [SPARK-32915][CORE] Network-layer and shuffle RPC layer changes to support push shuffle blocks

[GitBox <gi...@apache.org>]

otterc commented on a change in pull request #29855:
URL: https://github.com/apache/spark/pull/29855#discussion_r499976196



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File path: common/network-common/src/main/java/org/apache/spark/network/server/TransportRequestHandler.java
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@@ -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:
       @attilapiros 
   Why do you think that caching the metadata on the client is a better approach than sending this metadata back with the response?




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