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Posted to issues@spark.apache.org by "Apache Spark (JIRA)" <ji...@apache.org> on 2016/10/05 22:42:20 UTC
[jira] [Assigned] (SPARK-17791) Join reordering using star schema
detection
[ https://issues.apache.org/jira/browse/SPARK-17791?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Apache Spark reassigned SPARK-17791:
------------------------------------
Assignee: (was: Apache Spark)
> 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
> 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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