[jira] [Commented] (FLINK-1259) FilterFunction can modify data

["Stephan Ewen (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-1259?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14226392#comment-14226392 ] 

Stephan Ewen commented on FLINK-1259:
-------------------------------------

I vote to document that we strongly assume filter functions to not modify the data.
It seems like a reasonable assumption that should be easy to grasp.

> FilterFunction can modify data
> ------------------------------
>
>                 Key: FLINK-1259
>                 URL: https://issues.apache.org/jira/browse/FLINK-1259
>             Project: Flink
>          Issue Type: Bug
>          Components: Java API, Optimizer, Scala API
>    Affects Versions: 0.7.0-incubating
>            Reporter: Fabian Hueske
>
> The FilterFunction returns a boolean for an input record which determines whether the record is filtered or not. 
> However, the function can also modify the input record which has effects if the record is not filtered.
> The optimizer assumes that the data is not changed by a FilterFunction, i.e., it assumes that a Filter preserves physical data properties (orders, partitionings, etc.) and might also be pushed down in the future. These assumptions can result in semantically incorrect programs, if the function actually changes its incoming records.
> Possible solutions are:
> - document the requirements (and hope that users read it and behave nicely)
> - hand a copy to the function which can be modified but is not passed on. This has major performance implications and might confuse users as changes are invalidated. However, this could also be integrated with the mutable/immutable runtime switch (FLINK-1005)



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