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https://issues.apache.org/jira/browse/SPARK-14832?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Tathagata Das updated SPARK-14832:
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    Description: 
When creating a file stream using sqlContext.write.stream(), existing files are 
scanned twice for finding the schema 
- Once, when creating a DataSource + StreamingRelation in the 
DataFrameReader.stream()
- Again, when creating streaming Source from the DataSource, in 
DataSource.createSource()

Instead, the schema should be generated only once, at the time of creating the 
dataframe, and when the streaming source is created, it should just reuse that 
schema

  was:
When creating a file stream using sqlContext.write.stream(), existing files are 
scanned twice for finding the schema 
- Once, when creating a DataSource + StreamingRelation in the 
DataFrameReader.stream()
- Again, when creating streaming Source from the DataSource, in 
DataSource.createSource()

Instead, the schema should be generated only once, at the time of creating the 
dataframe, and when the streaming source is created, it should just reuse that 
schame


> Refactor DataSource to ensure schema is inferred only once when creating a 
> file stream
> --------------------------------------------------------------------------------------
>
>                 Key: SPARK-14832
>                 URL: https://issues.apache.org/jira/browse/SPARK-14832
>             Project: Spark
>          Issue Type: Sub-task
>          Components: SQL, Streaming
>            Reporter: Tathagata Das
>            Assignee: Tathagata Das
>
> When creating a file stream using sqlContext.write.stream(), existing files 
> are scanned twice for finding the schema 
> - Once, when creating a DataSource + StreamingRelation in the 
> DataFrameReader.stream()
> - Again, when creating streaming Source from the DataSource, in 
> DataSource.createSource()
> Instead, the schema should be generated only once, at the time of creating 
> the dataframe, and when the streaming source is created, it should just reuse 
> that schema



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