[jira] [Commented] (DRILL-6791) Merge scan projection framework into master

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DRILL-6791?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16647508#comment-16647508 ] 

ASF GitHub Bot commented on DRILL-6791:
---------------------------------------

paul-rogers opened a new pull request #1501: DRILL-6791: Scan projection framework
URL: https://github.com/apache/drill/pull/1501
 
 
   The "schema projection" mechanism:
   
   * Handles none (SELECT COUNT\(*)), some (SELECT a, b, x) and all (SELECT *) projection.
   * Handles null columns (for projection a column "x" that does not exist in the base table.)
   * Handles constant columns as used for file metadata (AKA "implicit" columns).
   * Handle schema persistence: the need to reuse the same vectors across different scanners
   * Provides a framework for consuming externally-supplied metadata
   * Since we don't yet have a way to provide "real" metadata, obtains metadata hints from previous batches and from the projection list (a.b implies that "a" is a map, c[0] implies that "c" is an array, etc.)
   * Handles merging the set of data source columns and null columns to create the final output batch.

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> Merge scan projection framework into master
> -------------------------------------------
>
>                 Key: DRILL-6791
>                 URL: https://issues.apache.org/jira/browse/DRILL-6791
>             Project: Apache Drill
>          Issue Type: Improvement
>    Affects Versions: 1.15.0
>            Reporter: Paul Rogers
>            Assignee: Paul Rogers
>            Priority: Major
>
> Merge the next set of "result set loader" code into master via a PR. This one covers the "schema projection" mechanism which:
> * Handles none (SELECT COUNT\(*)), some (SELECT a, b, x) and all (SELECT *) projection.
> * Handles null columns (for projection a column "x" that does not exist in the base table.)
> * Handles constant columns as used for file metadata (AKA "implicit" columns).
> * Handle schema persistence: the need to reuse the same vectors across different scanners
> * Provides a framework for consuming externally-supplied metadata
> * Since we don't yet have a way to provide "real" metadata, obtains metadata hints from previous batches and from the projection list (a.b implies that "a" is a map, c[0] implies that "c" is an array, etc.)
> * Handles merging the set of data source columns and null columns to create the final output batch.



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