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From "Prasanth Jayachandran (Jira)" <j...@apache.org>
Subject [jira] [Resolved] (HIVE-24061) Improve llap task scheduling for better cache hit rate
Date Wed, 26 Aug 2020 17:53:00 GMT

     [ https://issues.apache.org/jira/browse/HIVE-24061?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Prasanth Jayachandran resolved HIVE-24061.
------------------------------------------
    Fix Version/s: 4.0.0
       Resolution: Fixed

Merged to master. Thanks [~rajesh.balamohan] !

> Improve llap task scheduling for better cache hit rate 
> -------------------------------------------------------
>
>                 Key: HIVE-24061
>                 URL: https://issues.apache.org/jira/browse/HIVE-24061
>             Project: Hive
>          Issue Type: Improvement
>            Reporter: Rajesh Balamohan
>            Assignee: Rajesh Balamohan
>            Priority: Major
>              Labels: perfomance, pull-request-available
>             Fix For: 4.0.0
>
>          Time Spent: 50m
>  Remaining Estimate: 0h
>
> TaskInfo is initialized with the "requestTime and locality delay". When lots of vertices
are in the same level, "taskInfo" details would be available upfront. By the time, it gets
to scheduling, "requestTime + localityDelay" won't be higher than current time. Due to this,
it misses scheduling delay details and ends up choosing random node. This ends up missing
cache hits and reads data from remote storage.
> E.g Observed this pattern in Q75 of tpcds.
> Related lines of interest in scheduler: [https://github.com/apache/hive/blob/master/llap-tez/src/java/org/apache/hadoop/hive/llap/tezplugins/LlapTaskSchedulerService.java
|https://github.com/apache/hive/blob/master/llap-tez/src/java/org/apache/hadoop/hive/llap/tezplugins/LlapTaskSchedulerService.java]
> {code:java}
>    boolean shouldDelayForLocality = request.shouldDelayForLocality(schedulerAttemptTime);
> ..
> ..
>     boolean shouldDelayForLocality(long schedulerAttemptTime) {
>       return localityDelayTimeout > schedulerAttemptTime;
>     }
> {code}
>  
> Ideally, "localityDelayTimeout" should be adjusted based on it's first scheduling opportunity.



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