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https://issues.apache.org/jira/browse/HIVE-5775?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14041053#comment-14041053
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Laljo John Pullokkaran commented on HIVE-5775:
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Following may help in reducing the confusion:
1. In design doc the cost formula is for choosing Join Algorithm. The cost
formula as described in the doc assumes Tez execution.
2. However current work on CBO doesn’t include Join algorithm selection.
Instead it rearranges Join based on Join cardinality & NDV. In other words Join
reordering is not depended on Physical Execution Layer (Tez or MR).
3. When we decide to do Join Algorithm Selection we can fit in cost formula for
both a) MR b) Tez. This way, based on the physical execution layer we can
select best Join Algorithm/Order.
4. The cost formula for Join Algorithm selection is not that different between
MR & Tez (except for intermediate HDFS writes). So assume that CBO can support
both execution layers rather easily.
5. CBO framework allows you to plug and play any cost model. There is no hard
coupling.
> Introduce Cost Based Optimizer to Hive
> --------------------------------------
>
> Key: HIVE-5775
> URL: https://issues.apache.org/jira/browse/HIVE-5775
> Project: Hive
> Issue Type: New Feature
> Reporter: Laljo John Pullokkaran
> Assignee: Laljo John Pullokkaran
> Attachments: CBO-2.pdf, HIVE-5775.1.patch
>
>
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