Victsm commented on a change in pull request #29855:
URL: https://github.com/apache/spark/pull/29855#discussion_r500443538
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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 this is the approach I mentioned above, along with the
concern about no longer able to reuse callback object.
Let me try code it that way and benchmark it to see if this concern is real
or not.
> One way to do this without incurring any potential protocol change would
be to make BlockPushCallback inside OneForOneBlockPusher stateful.
Currently, that callback is stateless, so multiple invocations to
TransportClient#uploadStream for the same batch of blocks would reuse the same
callback object.
If we make that callback object stateful, to keep track of the additional
metadata ManagedBuffer, then the callback object would have what we need built
into it during object creation.
My concern during the implementation was the potential JVM pressure this
approach might generate, since we will create one callback object per block to
be pushed.
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