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https://issues.apache.org/jira/browse/RATIS-1176?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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runzhiwang updated RATIS-1176:
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Attachment: screenshot-7.png
> Benchmark various ways to stream data
> -------------------------------------
>
> Key: RATIS-1176
> URL: https://issues.apache.org/jira/browse/RATIS-1176
> Project: Ratis
> Issue Type: Sub-task
> Components: client, Streaming
> Reporter: Tsz-wo Sze
> Priority: Major
> Attachments: image-2020-11-25-07-40-50-383.png, screenshot-5.png,
> screenshot-6.png, screenshot-7.png, screenshot-8.png, screenshot-9.png
>
>
> In RATIS-1175, we provided a WritableByteChannel view of DataStreamOutput in
> order to support FileChannel.transferTo. However, [~runzhiwang] pointed out
> that sun.nio.ch.FileChannelImpl.transferTo has three submethods
> - transferToDirectly (fastest)
> - transferToTrustedChannel
> - transferToArbitraryChannel (slowest, requires buffer copying)
> Unfortunately, our current implementation only able to use
> transferToArbitraryChannel.
> There are several ideas below to improve the performance. We should
> benchmark them.
> # Improve the current implementation of WritableByteChannel so that it may be
> able to use a faster transferTo method.
> # Use
> [FileChannel.map(..)|https://docs.oracle.com/javase/8/docs/api/java/nio/channels/FileChannel.html#map-java.nio.channels.FileChannel.MapMode-long-long-]
> and pass MappedByteBuffer to our DataStreamOutput.writeAsync method.
> # Add a new API
> {code}
> //DataStreamOutput
> CompletableFuture<DataStreamReply> writeAsync(File);
> {code}
> Internally, use Netty DefaultFileRegion for zero-copy file transfer:
> https://github.com/netty/netty/blob/4.1/example/src/main/java/io/netty/example/file/FileServerHandler.java#L53
> The data flow of client -> primary -> peer as follows
> If stream file and do not calculate checksum, we use transferTo. In client,
> there are 1 DMA copy and 1 DMA gather copy, no CPU copy.
> !screenshot-1.png!
> If stream file and calculate checksum, we use MapByteBuffer. In client, there
> are 2 DMA copy and 1 CPU copy.
> !screenshot-2.png!
> If stream data not in file and calculate checksum, we use DirectByteBuffer.
> In client, there are 2 DMA copy and 2 CPU copy.
> !screenshot-3.png!
> we should avoid reading data into heap such as HeapByteBuffer. In client
> there are 2 DMA copy and 4 CPU copy.
> !screenshot-4.png!
> The following is flow before ratis streaming and use ProtoBuf to send data.
> In client there are 2 DMA copy and 4 CPU copy. In leader, there are 3 DMA
> copy and 7 CPU copy. In follower, there are 2 DMA copy and 5 CPU copy.
> !screenshot-5.png!
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