[jira] [Resolved] (SPARK-10659) DataFrames and SparkSQL saveAsParquetFile does not preserve REQUIRED (not nullable) flag in schema

["Hyukjin Kwon (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SPARK-10659?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Hyukjin Kwon resolved SPARK-10659.
----------------------------------
    Resolution: Incomplete

> DataFrames and SparkSQL saveAsParquetFile does not preserve REQUIRED (not nullable) flag in schema
> --------------------------------------------------------------------------------------------------
>
>                 Key: SPARK-10659
>                 URL: https://issues.apache.org/jira/browse/SPARK-10659
>             Project: Spark
>          Issue Type: Improvement
>          Components: SQL
>    Affects Versions: 1.3.0, 1.3.1, 1.4.0, 1.4.1, 1.5.0
>            Reporter: Vladimir Picka
>            Priority: Major
>              Labels: bulk-closed
>
> DataFrames currently automatically promotes all Parquet schema fields to optional when they are written to an empty directory. The problem remains in v1.5.0.
> The culprit is this code:
> {code}
> val relation = if (doInsertion) {
>       // This is a hack. We always set nullable/containsNull/valueContainsNull to true
>       // for the schema of a parquet data.
>       val df =
>         sqlContext.createDataFrame(
>           data.queryExecution.toRdd,
>           data.schema.asNullable)
>       val createdRelation =
>         createRelation(sqlContext, parameters, df.schema).asInstanceOf[ParquetRelation2]
>       createdRelation.insert(df, overwrite = mode == SaveMode.Overwrite)
>       createdRelation
>     }
> {code}
> which was implemented as part of this PR:
> https://github.com/apache/spark/commit/1b490e91fd6b5d06d9caeb50e597639ccfc0bc3b
> This very unexpected behaviour for some use cases when files are read from one place and written to another like small file packing - it ends up with incompatible files because required can't be promoted to optional normally. It is essence of a schema that it enforces "required" invariant on data. It should be supposed that it is intended.
> I believe that a better approach is to have default behaviour to keep schema as is and provide f.e. a builder method or option to allow forcing to optional.
> Right now we have to overwrite private API so that our files are rewritten as is with all its perils.
> Vladimir



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