[jira] [Resolved] (SPARK-9192) add initialization phase for nondeterministic expression

["Reynold Xin (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SPARK-9192?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Reynold Xin resolved SPARK-9192.
--------------------------------
       Resolution: Fixed
         Assignee: Wenchen Fan
    Fix Version/s: 1.5.0

> add initialization phase for nondeterministic expression
> --------------------------------------------------------
>
>                 Key: SPARK-9192
>                 URL: https://issues.apache.org/jira/browse/SPARK-9192
>             Project: Spark
>          Issue Type: Improvement
>          Components: SQL
>            Reporter: Wenchen Fan
>            Assignee: Wenchen Fan
>             Fix For: 1.5.0
>
>
> Currently nondeterministic expression is broken without a explicit initialization phase.
> Let me take `MonotonicallyIncreasingID` as an example. This expression need a mutable state to remember how many times it has been evaluated, so we use `@transient var count: Long` there. By being transient, the `count` will be reset to 0 and **only** to 0 when serialize and deserialize it, as deserialize transient variable will result to default value. There is *no way* to use another initial value for `count`, until we add the explicit initialization phase.
> For now no nondeterministic expression need this feature, but we may add new ones with the need of a different initial value for mutable state in the future.
> Another use case is local execution for LocalRelation, there is no serialize and deserialize phase and thus we can't reset mutable states for it.



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