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https://issues.apache.org/jira/browse/SPARK-9192?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14637124#comment-14637124
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Wenchen Fan commented on SPARK-9192:
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hi [~lian cheng], sorry about leaving the description empty at the beginning,
as it's a result of an offline discussion with rxin. I have updated it, does
this make sense to you?
> 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
>
> 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 a a 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.
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