[SPARK-17791] Join reordering using star schema detection

• Type: Sub-task
• Status: Resolved
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 2.1.0
• Fix Version/s: 2.2.0
• Component/s: SQL
• Target Version/s: 2.2.0
• Assignee: Ioana Delaney
• Reporter: Ioana Delaney
• Created: 05/Oct/16 22:19
• Updated: 20/Mar/17 08:08
• Resolved: 20/Mar/17 08:08

Description

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.

Issue Links

• is related to: SPARK-16026 Cost-based Optimizer Framework
• links to: [Github] Pull Request #15363 (ioana-delaney)