[jira] [Created] (SPARK-26088) DataSourceV2 should expose row count and attribute statistics

["Martin Junghanns (JIRA)" <ji...@apache.org>]

Martin Junghanns created SPARK-26088:
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             Summary: DataSourceV2 should expose row count and attribute statistics
                 Key: SPARK-26088
                 URL: https://issues.apache.org/jira/browse/SPARK-26088
             Project: Spark
          Issue Type: Improvement
          Components: SQL
    Affects Versions: 2.3.0
            Reporter: Martin Junghanns


During investigation of CBO and DataSourceV2 we found, that
{code}
org.apache.spark.sql.sources.v2.reader.Statistics
{code}
misses attribute/column statistics and that
{code}
DataSourceV2Relation#computeStats
{code}
wraps
{code}
org.apache.spark.sql.sources.v2.reader.Statistics
{code}
into
{code}
org.apache.spark.sql.catalyst.plans.logical.Statistics
{code}
without forwarding the optional {{rowCount}} if present.

However {{rowCount}} and {{attributeStats}} are used during CBO e.g. in {{JoinEstimation}} and {{AggregateEstimation}}.

We propose that:
* {{org.apache.spark.sql.sources.v2.reader.Statistics}} mirrors {{org.apache.spark.sql.catalyst.plans.logical.Statistics}} 
* {{DataSourceV2Relation}} forwards all the information to be available during CBO



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