Andrew Ray created SPARK-18457:
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Summary: ORC and other columnar formats using HiveShim read all
columns when doing a simple count
Key: SPARK-18457
URL: https://issues.apache.org/jira/browse/SPARK-18457
Project: Spark
Issue Type: Bug
Components: SQL
Affects Versions: 2.0.2, 1.6.3
Environment: Hadoop 2.7.0
Reporter: Andrew Ray
Priority: Minor
Doing a `select count(*) from a_orc_table` reads all columns and thus is slower
than a query selecting one like `select count(a_column) from a_orc_table`. Data
read can be seen in the UI (appears to only be accurate for Hadoop 2.5+ based
on comment in FileScanRDD.scala line 80).
I will create a PR shortly.
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