[jira] [Commented] (KAFKA-6486) TimeWindows causes unordered calls to windowed aggregation functions

["Guozhang Wang (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-6486?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16377760#comment-16377760 ] 

Guozhang Wang commented on KAFKA-6486:
--------------------------------------

Thanks for reporting this [~vale68] I think it is a good improvement to have.

Would you like to submit a PR for this issue?

> TimeWindows causes unordered calls to windowed aggregation functions
> --------------------------------------------------------------------
>
>                 Key: KAFKA-6486
>                 URL: https://issues.apache.org/jira/browse/KAFKA-6486
>             Project: Kafka
>          Issue Type: Improvement
>          Components: streams
>    Affects Versions: 1.0.0
>            Reporter: Valentino Proietti
>            Priority: Minor
>
> This is not a real bug but it causes some weird behaviour, at least in my opinion.
> The TimeWindows has a method called windowsFor() that uses and returns an HashMap:
>     @Override
>     *public* Map<Long, TimeWindow> windowsFor(*final* *long* timestamp) {
>         *long* windowStart = (Math._max_(0, timestamp - sizeMs + advanceMs) / advanceMs) * advanceMs;
>         *final* Map<Long, TimeWindow> windows = *new* HashMap<>();
>         ....
> the HashMap does not preserve the order of insertion and this ends up later in calls to any streams windowed aggregation functions that are not ordered by window time as I would expect.
> A simple solution is to replace the HashMap with a LinkedHashMap and that's what I did.
> Anyway replacing it directly in your code can save hours of debugging to understand what's happening.
> Thank you 
>  



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