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From "Rui Li (JIRA)" <>
Subject [jira] [Commented] (HIVE-17486) Enable SharedWorkOptimizer in tez on HOS
Date Thu, 02 Nov 2017 03:28:02 GMT


Rui Li commented on HIVE-17486:

Hi [~kellyzly],
bq. In tez, Map can be connected 2 Reducers while in spark, we can not do this.
My understanding is HoS also supports one Map connecting to multiple Reducers - that's what
{{CombineEquivalentWorkResolver}} is intended for and there're some example queries in {{dynamic_rdd_cache.q}}.
The problem here is HoS doesn't merge equivalent works as aggressively as HoT does. Is that

> Enable SharedWorkOptimizer in tez on HOS
> ----------------------------------------
>                 Key: HIVE-17486
>                 URL:
>             Project: Hive
>          Issue Type: Bug
>            Reporter: liyunzhang
>            Assignee: liyunzhang
>            Priority: Major
>         Attachments: 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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