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https://issues.apache.org/jira/browse/SPARK-21176?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Apache Spark reassigned SPARK-21176:
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Assignee: (was: Apache Spark)
> Master UI hangs with spark.ui.reverseProxy=true if the master node has many
> CPUs
> --------------------------------------------------------------------------------
>
> Key: SPARK-21176
> URL: https://issues.apache.org/jira/browse/SPARK-21176
> Project: Spark
> Issue Type: Bug
> Components: Web UI
> Affects Versions: 2.1.0, 2.1.1, 2.2.0, 2.2.1
> Environment: ppc64le GNU/Linux, POWER8, only master node is reachable
> externally other nodes are in an internal network
> Reporter: Ingo Schuster
> Labels: network, web-ui
>
> In reverse proxy mode, Sparks exhausts the Jetty thread pool if the master
> node has too many cpus or the cluster has too many executers:
> For each ProxyServlet, Jetty creates Selector threads: minimum 4, maximum
> half the number of available CPUs:
> {{this(Math.max(1, Runtime.getRuntime().availableProcessors() / 2));}}
> (see
> https://github.com/eclipse/jetty.project/blob/0c8273f2ca1f9bf2064cd9c4c939d2546443f759/jetty-client/src/main/java/org/eclipse/jetty/client/http/HttpClientTransportOverHTTP.java)
> In reverse proxy mode, a proxy servlet is set up for each executor.
> I have a system with 7 executors and 88 CPUs on the master node. Jetty tries
> to instantiate 7*44 = 309 selector threads just for the reverse proxy
> servlets, but since the QueuedThreadPool is initialized with 200 threads by
> default, the UI gets stuck.
> I have patched JettyUtils.scala to extend the thread pool ( {{val pool = new
> QueuedThreadPool(400)}}). With this hack, the UI works.
> Obviously, the Jetty defaults are meant for a real web server. If that has 88
> CPUs, you do certainly expect a lot of traffic.
> For the Spark admin UI however, there will rarely be concurrent accesses for
> the same application or the same executor.
> I therefore propose to dramatically reduce the number of selector threads
> that get instantiated - at least by default.
> I will propose a fix in a pull request.
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