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https://issues.apache.org/jira/browse/SPARK-21338?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16172750#comment-16172750
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Apache Spark commented on SPARK-21338:
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User 'viirya' has created a pull request for this issue:
https://github.com/apache/spark/pull/19286
> AggregatedDialect doesn't override isCascadingTruncateTable() method
> --------------------------------------------------------------------
>
> Key: SPARK-21338
> URL: https://issues.apache.org/jira/browse/SPARK-21338
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 2.1.0, 2.1.1
> Reporter: Ostap Gonchar
> Assignee: Huaxin Gao
> Fix For: 2.3.0
>
>
> org.apache.spark.sql.jdbc.JdbcDialect's method:
> *def isCascadingTruncateTable(): Option[Boolean] = None*
> is not overriden in org.apache.spark.sql.jdbc.AggregatedDialect class.
> Because of this issue - *+when you add more than one dialect Spark doesn't
> truncate table because isCascadingTruncateTable always returns default None
> for Aggregated Dialect+*.
> Can be tracked when you write dataset in jdbc mode with SaveMode.Overwrite
> and extra JdbcDialect added via JdbcDialects.registerDialect(...); method.
> Then inside of
> org.apache.spark.sql.execution.datasources.jdbc.JdbcRelationProvider on line
> 65 in createRelation method it will never get to line 67 even if isTruncate
> returns true.
> It will only get inside if you have one JdbcDialect and AggregatedDialect is
> not used.
> Fix would be to overrite this method in AggregatedDialect and also to reduce
> value (I guess with and clause same as in overriden getHandle method) e.g.
> override def isCascadingTruncateTable(): Option[Boolean]=
> Some(dialects.map(_.isCascadingTruncateTable()).reduce(_ && _))
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