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https://issues.apache.org/jira/browse/HIVE-7905?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Harish Butani updated HIVE-7905:
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Attachment: HIVE-7905.2.patch
> CBO: more cost model changes
> ----------------------------
>
> Key: HIVE-7905
> URL: https://issues.apache.org/jira/browse/HIVE-7905
> Project: Hive
> Issue Type: Sub-task
> Components: CBO
> Reporter: Harish Butani
> Assignee: Harish Butani
> Attachments: HIVE-7905.2.patch, exp-backoff-vs-log-smoothing
>
>
> 1. For composite predicates smoothen the Selectivity calculation using
> +exponential backoff+. Thanks to [~ mmokhtar] for this formula.
> {quote}
> Can you change the algorithm to use exponential back-off :
> ndv(pe0) * ndv(pe1) ^(1/2) * ndv(pe2) ^(1/4) * ndv(pe3) ^(1/8)
> Opposed to :
> ndv(pex)*log(ndv(pe1))*log(ndv(pe2))
> If we assume selectivity of 0.7 for each store_sales join then join
> selectivity can end up being 6.24285E-05 which is too low and eventually
> results in an un-optimal plan.
> {quote}
> See attached picture.
> 2. In case of Fact - Dim joins on the Dim primary key we infer the Join
> cardinality as a filter on the Fact table:
> {code}
> join card = rowCount(Fact table) * selectivity(dim table)
> {code}
> Whether a Column is a Key is inferred based on either:
> * table rowCount = column ndv
> * (tbd shortly) table rowCount = (maxVal - minVal)
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