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From "Matthias J. Sax (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (KAFKA-4750) KeyValueIterator returns null values
Date Fri, 21 Jul 2017 04:54:00 GMT

    [ https://issues.apache.org/jira/browse/KAFKA-4750?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16095776#comment-16095776
] 

Matthias J. Sax commented on KAFKA-4750:
----------------------------------------

I understand what you are saying, but encoding an empty collection into {{null}} would not
work after all, as if we write this to the changelog, it might get delete during compaction
resulting in potential data loss. Thus, Streams is limited by the underlying broker semantics
and thus, users need to encode empty collections as not-null value anyway.

> KeyValueIterator returns null values
> ------------------------------------
>
>                 Key: KAFKA-4750
>                 URL: https://issues.apache.org/jira/browse/KAFKA-4750
>             Project: Kafka
>          Issue Type: Bug
>          Components: streams
>    Affects Versions: 0.10.1.1, 0.10.2.1, 0.11.0.0
>            Reporter: Michal Borowiecki
>            Assignee: Evgeny Veretennikov
>              Labels: newbie
>         Attachments: DeleteTest.java
>
>
> The API for ReadOnlyKeyValueStore.range method promises the returned iterator will not
return null values. However, after upgrading from 0.10.0.0 to 0.10.1.1 we found null values
are returned causing NPEs on our side.
> I found this happens after removing entries from the store and I found resemblance to
SAMZA-94 defect. The problem seems to be as it was there, when deleting entries and having
a serializer that does not return null when null is passed in, the state store doesn't actually
delete that key/value pair but the iterator will return null value for that key.
> When I modified our serilizer to return null when null is passed in, the problem went
away. However, I believe this should be fixed in kafka streams, perhaps with a similar approach
as SAMZA-94.



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