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Posted to issues@spark.apache.org by "Apache Spark (JIRA)" <ji...@apache.org> on 2018/10/31 13:01:00 UTC
[jira] [Assigned] (SPARK-25894) Include a count of the number of
physical columns read for a columnar data source in the metadata of
FileSourceScanExec
[ https://issues.apache.org/jira/browse/SPARK-25894?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Apache Spark reassigned SPARK-25894:
------------------------------------
Assignee: Apache Spark
> Include a count of the number of physical columns read for a columnar data source in the metadata of FileSourceScanExec
> -----------------------------------------------------------------------------------------------------------------------
>
> Key: SPARK-25894
> URL: https://issues.apache.org/jira/browse/SPARK-25894
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 2.4.0
> Reporter: Michael Allman
> Assignee: Apache Spark
> Priority: Minor
>
> Knowing the number of physical columns Spark will read from a columnar file format (such as Parquet) is extremely helpful (if not critical) in validating an assumption about that number of columns based on a given query and schema pruning functionality. For example, take a {{contacts}} table with a {{name}} struct like {{name.first, name.last}}. Without schema pruning the following query reads both columns in the {{name}} struct:
> {{select name.first from contacts}}
> With schema pruning, the same query reads only the {{name.first}} column.
> This issue (and related PR) proposes an additional metadata field for {{FileSourceScanExec}} which identifies the number of columns Spark will read from that file source. This metadata will be printed as part of a physical plan explanation.
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