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From "Matthias J. Sax (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (KAFKA-4750) KeyValueIterator returns null values
Date Thu, 20 Jul 2017 11:46:00 GMT

    [ https://issues.apache.org/jira/browse/KAFKA-4750?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16094568#comment-16094568
] 

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

As mentioned above. I would go with option (1) as null delete semantics also align with changelog
delete semantics. Also, if we would allow to put {{null}} as regular value, we have the same
issue as Java has in general: if a {{get}} returns {{null}} it's unclear if {{null}} is a
regular value or the key is just not there. Within Java (eg. {{HashMap}}) you still can check
with {{containsKey}} but we don't have an API for this on the stores.

> 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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