Chesnay Schepler created FLINK-19056:
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Summary: 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
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. It would
seem a reasonable thing to do since we at least should be able to skip a bunch
of memory copies?
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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