Ioana Delaney created SPARK-17791:
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Summary: 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
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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