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https://issues.apache.org/jira/browse/FLINK-19056?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17186380#comment-17186380
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Till Rohrmann commented on FLINK-19056:
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[~chesnay] is this a blocker if we decide to upgrade to Netty 4.1.49 for the
{{1.12.0}} release?
> Investigate multipart upload performance regression
> ---------------------------------------------------
>
> Key: FLINK-19056
> URL: https://issues.apache.org/jira/browse/FLINK-19056
> Project: Flink
> Issue Type: Task
> Components: Runtime / REST
> Affects Versions: 1.12.0
> Reporter: Chesnay Schepler
> Priority: Blocker
> Fix For: 1.12.0
>
>
> When using Netty 4.1.50 the multipart upload of files is more than a 100
> times slower in the {{FileUploadHandlerTest}}.
> This test has traditionally been somewhat heavy, since it repeatedly tests
> the upload of 60mb files.
> On my machine this test currently finishes in 2-3 seconds, but with the
> upgraded Netty version it runs for several _minutes_ instead. I have not
> verified yet whether this is purely an issue of the test, but I would
> consider it unlikely.
> This would make Flink effectively unusable when uploading larger jars or
> JobGraphs.
>
> My theore is that is due to [this|https://github.com/netty/netty/pull/10226]
> change in Netty.
> Before this change, the {{HttpPostMultipartRequestDecoder}} was always
> creating unpooled heap buffers for _something_; after the change the buffer
> type is dependent on the input buffer. The input buffer is a direct one, so
> my conclusion is that with the upgrade we ended up allocating more direct
> buffers than we did previously.
>
> One solution I found was to explicitly create an {{UnpooledByteBufAllocator}}
> for the {{RestServerEndpoint}} that prefers heap buffers, which results in
> the input buffer to be a heap buffer, and thus we are never allocating direct
> ones.
> However, this should also imply that we are creating more heap buffers than
> we did in the previously; I don't know how much of a problem that is. Maybe
> this is even a good thing if it means less copies from direct to heap memory,
> but
> [this|https://github.com/netty/netty/blob/8f7ca2b4ef53b94607992494adf17a6237df7356/codec-http/src/main/java/io/netty/handler/codec/http/multipart/HttpPostMultipartRequestDecoder.java#L332]
> comment seems to indicate otherwise.
> {code:java}
> +final ByteBufAllocator byteBufAllocator = new
> UnpooledByteBufAllocator(false);
> +
> bootstrap = new ServerBootstrap();
> bootstrap
> .group(bossGroup, workerGroup)
> .channel(NioServerSocketChannel.class)
> - .childHandler(initializer);
> + .childHandler(initializer)
> + .option(ChannelOption.ALLOCATOR, byteBufAllocator)
> + .childOption(ChannelOption.ALLOCATOR, byteBufAllocator);
> {code}
>
> On a somewhat related note, we could think about increasing the chunkSize
> from 8kb to 64kb to reduce the GC pressure a bit, along with some arenas for
> the REST API.
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