[jira] [Commented] (SPARK-2962) Suboptimal scheduling in spark

["Nan Zhu (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-2962?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14167144#comment-14167144 ] 

Nan Zhu commented on SPARK-2962:
--------------------------------

Hi, [~mridulm@yahoo-inc.com]

I think this has been fixed in https://github.com/apache/spark/pull/1313/files,

{code:title=TaskSetManager.scala|borderStyle=solid}

if (tasks(index).preferredLocations == Nil) {
       addTo(pendingTasksWithNoPrefs)
     }
{code}

Now, only tasks without explicit preference is added to pendingTasksWithNoPrefs, and NO_PREF tasks are always scheduled after NODE_LOCAL




> Suboptimal scheduling in spark
> ------------------------------
>
>                 Key: SPARK-2962
>                 URL: https://issues.apache.org/jira/browse/SPARK-2962
>             Project: Spark
>          Issue Type: Bug
>          Components: Spark Core
>    Affects Versions: 1.1.0
>         Environment: All
>            Reporter: Mridul Muralidharan
>
> In findTask, irrespective of 'locality' specified, pendingTasksWithNoPrefs are always scheduled with PROCESS_LOCAL
> pendingTasksWithNoPrefs contains tasks which currently do not have any alive locations - but which could come in 'later' : particularly relevant when spark app is just coming up and containers are still being added.
> This causes a large number of non node local tasks to be scheduled incurring significant network transfers in the cluster when running with non trivial datasets.
> The comment "// Look for no-pref tasks after rack-local tasks since they can run anywhere." is misleading in the method code : locality levels start from process_local down to any, and so no prefs get scheduled much before rack.
> Also note that, currentLocalityIndex is reset to the taskLocality returned by this method - so returning PROCESS_LOCAL as the level will trigger wait times again. (Was relevant before recent change to scheduler, and might be again based on resolution of this issue).
> Found as part of writing test for SPARK-2931
>  



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