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https://issues.apache.org/jira/browse/SPARK-30512?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Thomas Graves resolved SPARK-30512.
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Fix Version/s: 3.0.0
Resolution: Fixed
this could be pulled back into branch-2.X as well
> Use a dedicated boss event group loop in the netty pipeline for external
> shuffle service
> ----------------------------------------------------------------------------------------
>
> Key: SPARK-30512
> URL: https://issues.apache.org/jira/browse/SPARK-30512
> Project: Spark
> Issue Type: Bug
> Components: Shuffle
> Affects Versions: 3.0.0
> Reporter: Chandni Singh
> Priority: Major
> Fix For: 3.0.0
>
>
> We have been seeing a large number of SASL authentication (RPC requests)
> timing out with the external shuffle service.
> The issue and all the analysis we did is described here:
> [https://github.com/netty/netty/issues/9890]
> I added a {{LoggingHandler}} to netty pipeline and realized that even the
> channel registration is delayed by 30 seconds.
> In the Spark External Shuffle service, the boss event group and the worker
> event group are same which is causing this delay.
> {code:java}
> EventLoopGroup bossGroup =
> NettyUtils.createEventLoop(ioMode, conf.serverThreads(),
> conf.getModuleName() + "-server");
> EventLoopGroup workerGroup = bossGroup;
> bootstrap = new ServerBootstrap()
> .group(bossGroup, workerGroup)
> .channel(NettyUtils.getServerChannelClass(ioMode))
> .option(ChannelOption.ALLOCATOR, allocator)
> .childOption(ChannelOption.ALLOCATOR, allocator);
> {code}
> When the load at the shuffle service increases, since the worker threads are
> busy with existing channels, registering new channels gets delayed.
> The fix is simple. I created a dedicated boss thread event loop group with 1
> thread.
> {code:java}
> EventLoopGroup bossGroup = NettyUtils.createEventLoop(ioMode, 1,
> conf.getModuleName() + "-boss");
> EventLoopGroup workerGroup = NettyUtils.createEventLoop(ioMode,
> conf.serverThreads(),
> conf.getModuleName() + "-server");
> bootstrap = new ServerBootstrap()
> .group(bossGroup, workerGroup)
> .channel(NettyUtils.getServerChannelClass(ioMode))
> .option(ChannelOption.ALLOCATOR, allocator)
> {code}
> This fixed the issue.
> We just need 1 thread in the boss group because there is only a single
> server bootstrap.
>
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