[jira] [Commented] (SPARK-21829) Enable config to permanently blacklist a list of nodes

["Luca Canali (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-21829?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17649234#comment-17649234 ] 

Luca Canali commented on SPARK-21829:
-------------------------------------

Note: similar functionality was later implemented in https://issues.apache.org/jira/browse/SPARK-26688

> Enable config to permanently blacklist a list of nodes
> ------------------------------------------------------
>
>                 Key: SPARK-21829
>                 URL: https://issues.apache.org/jira/browse/SPARK-21829
>             Project: Spark
>          Issue Type: New Feature
>          Components: Scheduler, Spark Core
>    Affects Versions: 2.1.1, 2.2.0
>            Reporter: Luca Canali
>            Priority: Minor
>
> The idea for this proposal comes from a performance incident in a local cluster where a job was found very slow because of a log tail of stragglers due to 2 nodes in the cluster being slow to access a remote filesystem.
> The issue was limited to the 2 machines and was related to external configurations: the 2 machines that performed badly when accessing the remote file system were behaving normally for other jobs in the cluster (a shared YARN cluster).
> With this new feature I propose to introduce a mechanism to allow users to specify a list of nodes in the cluster where executors/tasks should not run for a specific job.
> The proposed implementation that I tested (see PR) uses the Spark blacklist mechanism. With the parameter spark.blacklist.alwaysBlacklistedNodes, a list of user-specified nodes is added to the blacklist at the start of the Spark Context and it is never expired. 
> I have tested this on a YARN cluster on a case taken from the original production problem and I confirm a performance improvement of about 5x for the specific test case I have. I imagine that there can be other cases where Spark users may want to blacklist a set of nodes. This can be used for troubleshooting, including cases where certain nodes/executors are slow for a given workload and this is caused by external agents, so the anomaly is not picked up by the cluster manager.



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