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https://issues.apache.org/jira/browse/SPARK-15687?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15310663#comment-15310663
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Kazuaki Ishizaki commented on SPARK-15687:
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Thank you for creating interesting JIRA entry. Based on my experiments
(SPARK-13805, SPARK-14098, SPARK-15117, and SPARK-15380) to enable columnar
storage at whole stage codegen, I have some (implementation perspective?)
questions:
* How we pass columnar format among operators? Currently, we use
{{Iterater(Row)}} to pass data between operators.
* Who decides which (columnar or row-oriented) data format? Logical planner,
Physical planner, or others?
* Will we use Apache Arrow format as an internal format?
* We have two internal columnar formats: {{ColumnarBatch}} and {{CachedBatch}}.
Will we integrate these two into one?
> Columnar execution engine
> -------------------------
>
> Key: SPARK-15687
> URL: https://issues.apache.org/jira/browse/SPARK-15687
> Project: Spark
> Issue Type: New Feature
> Components: SQL
> Reporter: Reynold Xin
> Priority: Critical
>
> This ticket tracks progress in making the entire engine columnar, especially
> in the context of nested data type support.
> In Spark 2.0, we have used the internal column batch interface in Parquet
> reading (via a vectorized Parquet decoder) and low cardinality aggregation.
> Other parts of the engine are already using whole-stage code generation,
> which is in many ways more efficient than a columnar execution engine for
> flat data types.
> The goal here is to figure out a story to work towards making column batch
> the common data exchange format between operators outside whole-stage code
> generation, as well as with external systems (e.g. Pandas).
> Some of the important questions to answer are:
> From the architectural perspective:
> - What is the end state architecture?
> - Should aggregation be columnar?
> - Should sorting be columnar?
> - How do we encode nested data? What are the operations on nested data, and
> how do we handle these operations in a columnar format?
> - What is the transition plan towards the end state?
> From an external API perspective:
> - Can we expose a more efficient column batch user-defined function API?
> - How do we leverage this to integrate with 3rd party tools?
> - Can we have a spec for a fixed version of the column batch format that can
> be externalized and use that in data source API v2?
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