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https://issues.apache.org/jira/browse/HIVE-23443?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17105809#comment-17105809
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Gopal Vijayaraghavan commented on HIVE-23443:
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bq. 1) If guaranteed or finishable, the task should not be in pre-emption queue
This is very suspiciously like the pre-WLM model (which we know works without
deadlocks), but there's no way to fix pool based preemption if a speculative
finishable takes over a whole cluster.
> LLAP speculative task pre-emption seems to be not working
> ---------------------------------------------------------
>
> Key: HIVE-23443
> URL: https://issues.apache.org/jira/browse/HIVE-23443
> Project: Hive
> Issue Type: Bug
> Reporter: Prasanth Jayachandran
> Assignee: Prasanth Jayachandran
> Priority: Major
> Attachments: HIVE-23443.1.patch
>
>
> I think after HIVE-23210 we are getting a stable sort order and it is causing
> pre-emption to not work in certain cases.
> {code:java}
> "attempt_1589167813851_0000_119_01_000008_0
> (hive_20200511055921_89598f09-19f1-4969-ab7a-82e2dd796273-119/Map 1, started
> at 2020-05-11 05:59:22, in preemption queue, can finish)",
> "attempt_1589167813851_0008_84_01_000008_1
> (hive_20200511055928_7ae29ca3-e67d-4d1f-b193-05651023b503-84/Map 1, started
> at 2020-05-11 06:00:23, in preemption queue, can finish)" {code}
> Scheduler only peek's at the pre-emption queue and looks at whether it is
> non-finishable.
> [https://github.com/apache/hive/blob/master/llap-server/src/java/org/apache/hadoop/hive/llap/daemon/impl/TaskExecutorService.java#L420]
> In the above case, all tasks are speculative but state change is not
> triggering pre-emption queue re-ordering so peek() always returns canFinish
> task even though non-finishable tasks are in the queue.
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