[SPARK-24763] Remove redundant key data from value in streaming aggregation

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Done
• Affects Version/s: 2.4.0
• Fix Version/s: 2.4.0
• Component/s: Structured Streaming
• Assignee: Jungtaek Lim
• Reporter: Jungtaek Lim
• Created: 09/Jul/18 04:43
• Updated: 21/Sep/18 07:15
• Resolved: 21/Aug/18 22:23

Description

Key/Value of state in streaming aggregation is formatted as below:

• key: UnsafeRow containing group-by fields
• value: UnsafeRow containing key fields and another fields for aggregation results

which data for key is stored to both key and value.

This is to avoid doing projection row to value while storing, and joining key and value to restore origin row to boost performance, but while doing a simple benchmark test, I found it not much helpful compared to "project and join". (will paste test result in comment)

So I would propose a new option: remove redundant in stateful aggregation. I'm avoiding to modify default behavior of stateful aggregation, because state value will not be compatible between current and option enabled.

Issue Links

• links to: [Github] Pull Request #21733 (HeartSaVioR)