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https://issues.apache.org/jira/browse/HIVE-17486?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16221992#comment-16221992
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liyunzhang commented on HIVE-17486:
-----------------------------------
In tez, Map can be connected 2 Reducers while in spark, we can not do this. In
above example,
{code}
Map 1 <- Map 4 (BROADCAST_EDGE)
Reducer 2 <- Map 1 (SIMPLE_EDGE), Reducer 3 (BROADCAST_EDGE)
Reducer 3 <- Map 1 (SIMPLE_EDGE)
{code}
There are 2 edges from Map1 to other vertexes( Map1->Reducer3, Map1->Reducer2)
> 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
>
> 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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