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From "Laljo John Pullokkaran (JIRA)" <>
Subject [jira] [Commented] (HIVE-5775) Introduce Cost Based Optimizer to Hive
Date Mon, 23 Jun 2014 18:07:26 GMT


Laljo John Pullokkaran commented on HIVE-5775:

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:
>             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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