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https://issues.apache.org/jira/browse/HADOOP-11552?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14312783#comment-14312783
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Colin Patrick McCabe commented on HADOOP-11552:
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Hi [~sseth], can you explain the approach you're planning to take in more
detail? Are you proposing to keep the TCP session open, but reuse the handler
thread for something else, while the RPC is progressing? It seems like this
approach would alleviate the handler thread bottleneck, but potentially run
into another bottleneck by keeping open a lot of open TCP sockets (file
descriptors). Given that we've had problems with hitting max file descriptors
in the past, couldn't this be problematic?
Heartbeats are fundamental to how YARN works. If we move to an offer-based
system like Mesos, it seems like the way to do it would be to have the resource
manager make outgoing connections to the executors, rather than keeping TCP
sessions open a long time.
> Allow handoff on the server side for RPC requests
> -------------------------------------------------
>
> Key: HADOOP-11552
> URL: https://issues.apache.org/jira/browse/HADOOP-11552
> Project: Hadoop Common
> Issue Type: Improvement
> Components: ipc
> Reporter: Siddharth Seth
> Assignee: Siddharth Seth
> Attachments: HADOOP-11552.1.wip.txt
>
>
> An RPC server handler thread is tied up for each incoming RPC request. This
> isn't ideal, since this essentially implies that RPC operations should be
> short lived, and most operations which could take time end up falling back to
> a polling mechanism.
> Some use cases where this is useful.
> - YARN submitApplication - which currently submits, followed by a poll to
> check if the application is accepted while the submit operation is written
> out to storage. This can be collapsed into a single call.
> - YARN allocate - requests and allocations use the same protocol. New
> allocations are received via polling.
> The allocate protocol could be split into a request/heartbeat along with a
> 'awaitResponse'. The request/heartbeat is sent only when there's a request or
> on a much longer heartbeat interval. awaitResponse is always left active with
> the RM - and returns the moment something is available.
> MapReduce/Tez task to AM communication is another example of this pattern.
> The same pattern of splitting calls can be used for other protocols as well.
> This should serve to improve latency, as well as reduce network traffic since
> the keep-alive heartbeat can be sent less frequently.
> I believe there's some cases in HDFS as well, where the DN gets told to
> perform some operations when they heartbeat into the NN.
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