[jira] [Commented] (KUDU-2077) Return data in Apache Arrow format

["Grant Henke (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KUDU-2077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17124215#comment-17124215 ] 

Grant Henke commented on KUDU-2077:
-----------------------------------

This is resolved via the new "Apache Arrow Compatible" Columnar format added here:
* https://github.com/apache/kudu/commit/fa2d4c756646b3f8428d2931113e8dfc3bc5af79
* https://github.com/apache/kudu/commit/36a21d6ee4de8828417d7884cf87cd5e2ba15a21

We still need to validate arrow compliance in tests. Currently the plan is to leverage the Python and Java/Spark integrations/tests for ongoing validation.

> Return data in Apache Arrow format
> ----------------------------------
>
>                 Key: KUDU-2077
>                 URL: https://issues.apache.org/jira/browse/KUDU-2077
>             Project: Kudu
>          Issue Type: New Feature
>          Components: client, server
>            Reporter: Andrew Wong
>            Priority: Major
>              Labels: roadmap-candidate
>
> Dan and I spent the hackathon tinkering with the Apache Arrow format. Arrow is an in-memory columnar format designed to be the common data format for a large number of projects, see [here|https://arrow.apache.org]. One place we thought adding this would be particularly fitting is when sending results back to the client, since this currently returns row-wise data. By returning Arrow, this could open the door to simpler and faster integration with other projects.
> The server-side changes can be localized to the tablet service and wire protocol. We considered using Arrow more exhaustively throughout the server codebase, but found that because Arrow and Kudu's own in-memory format (i.e. that in kudu::ColumnBlock) are so similar, a simpler approach is to copy the buffers from ColumnBlock to the scan response and build arrow::Arrays client-side. A POC of the server-side changes can be found here: https://github.com/danburkert/kudu/tree/arrow
> At the time of writing this, the arrow::Array type has a varying number of arrow::Buffers, depending on the data type (e.g. one for null bitmaps, one for data, etc). The ColumnBlock "buffers" (i.e. data, null_bitmap) should be compatible with these Buffers with a couple of modifications:
> * The null-bitmaps in arrow are the complement of those used by Kudu
> * The RowBlock that owns the ColumnBlocks has a selection vector needs to be accounted for
> If the buffers are transferred over the wire (via sidecars or protobuf), they should be able to be converted to Arrays via arrow::ArrayData or directly via the Array constructors.



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