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From "liyunzhang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-17486) Enable SharedWorkOptimizer in tez on HOS
Date Fri, 08 Dec 2017 09:17:06 GMT

    [ https://issues.apache.org/jira/browse/HIVE-17486?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16283241#comment-16283241
] 

liyunzhang commented on HIVE-17486:
-----------------------------------

[~xuefuz] and [~lirui]: the second problem I found  is the modification of MapOperator after
changing from M->R to M->M->R.  
MapOperator  is reponsible for deserializing and  [initObjectInspector| https://github.com/apache/hive/blob/master/ql/src/java/org/apache/hadoop/hive/ql/exec/MapOperator.java#L170].
For the second M in M->M->R,  deserializing is not necessary and initObjectInspector
is necessary. Currently I am investigating how to make this work. If there is some wrong in
my understanding, please tell me!

> Enable SharedWorkOptimizer in tez on HOS
> ----------------------------------------
>
>                 Key: HIVE-17486
>                 URL: https://issues.apache.org/jira/browse/HIVE-17486
>             Project: Hive
>          Issue Type: Bug
>            Reporter: liyunzhang
>            Assignee: liyunzhang
>         Attachments: HIVE-17486.1.patch, explain.28.share.false, explain.28.share.true,
scanshare.after.svg, scanshare.before.svg
>
>
> in HIVE-16602, Implement shared scans with Tez.
> Given a query plan, the goal is to identify scans on input tables that can be merged
so the data is read only once. Optimization will be carried out at the physical level.  In
Hive on Spark, it caches the result of spark work if the spark work is used by more than 1
child spark work. After sharedWorkOptimizer is enabled in physical plan in HoS, the identical
table scans are merged to 1 table scan. This result of table scan will be used by more 1 child
spark work. Thus we need not do the same computation because of cache mechanism.



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