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https://issues.apache.org/jira/browse/SPARK-17791?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15621070#comment-15621070
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Zhenhua Wang commented on SPARK-17791:
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Hi Ioana,
The current implementation is NOT ready because we need to refactor the
statistics structure to make it easier to use during cost estimation, it won't
be stable until we finish the estimation part. I think it is necessary and
important to use CBO based RI. You can start to incorporate it in the algorithm
and rebase after the related code refactor is finished. Thanks.
> Join reordering using star schema detection
> -------------------------------------------
>
> Key: SPARK-17791
> URL: https://issues.apache.org/jira/browse/SPARK-17791
> Project: Spark
> Issue Type: Sub-task
> Components: SQL
> Affects Versions: 2.1.0
> Reporter: Ioana Delaney
> Assignee: Ioana Delaney
> Priority: Critical
> Attachments: StarJoinReordering1005.doc
>
>
> This JIRA is a sub-task of SPARK-17626.
> The objective is to provide a consistent performance improvement for star
> schema queries. Star schema consists of one or more fact tables referencing a
> number of dimension tables. In general, queries against star schema are
> expected to run fast because of the established RI constraints among the
> tables. This design proposes a join reordering based on natural, generally
> accepted heuristics for star schema queries:
> * Finds the star join with the largest fact table and places it on the
> driving arm of the left-deep join. This plan avoids large tables on the
> inner, and thus favors hash joins.
> * Applies the most selective dimensions early in the plan to reduce the
> amount of data flow.
> The design description is included in the below attached document.
> \\
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