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Posted to issues@spark.apache.org by "Douglas Colkitt (JIRA)" <ji...@apache.org> on 2019/02/19 22:35:00 UTC

[jira] [Created] (SPARK-26935) Skip DataFrameReader's CSV first line scan when not used

Douglas Colkitt created SPARK-26935:
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             Summary: Skip DataFrameReader's CSV first line scan when not used
                 Key: SPARK-26935
                 URL: https://issues.apache.org/jira/browse/SPARK-26935
             Project: Spark
          Issue Type: Improvement
          Components: SQL
    Affects Versions: 2.4.0
         Environment: Spark Version 2.4.0

Linux kernel 4.9.0-8-amd64 on Debian 9

Docker container on Google Kubernetes Engine VM (n1-standard-8)

 
            Reporter: Douglas Colkitt


DataFrameReader always collects the first line from the first partition on every csv() call. This is used for schema inference and header filtering. But if schema is pre-specified by the user and header is false, there's no point.

For certain cases CSV dataset generation is expensive and slow, and this clogs up the entire executor with 1 job to grab 1 line. If it's not needed, skipping the first line step is a free lunch for runtime and efficiency. 



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