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From "Guozhang Wang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (KAFKA-4750) KeyValueIterator returns null values
Date Thu, 20 Jul 2017 17:40:00 GMT

    [ https://issues.apache.org/jira/browse/KAFKA-4750?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16095052#comment-16095052

Guozhang Wang commented on KAFKA-4750:

I think technically I'm convinced that option (1) should be a better approach, the only reason
that I'm a bit hesitant in that is as [~mihbor] and [~evis] discussed previously on this ticket
that, for example:

An example use case would be if the value types are collections. In order to avoid dealing
with nulls in the application layer, one might want to deserialize null into an empty collection
and vice-versa. Would that be a valid use-case? I can't see why not, but I may be wrong.

Or more generally are there any common and valid use cases where users do want to de-serde
a not-null object into null bytes, or vice versa. Thinking about it a bit more, maybe enforcing
{{null objects <---> null bytes (meaning deletion)}} is not too bad since for such use
cases above users can still use some other non-null sentinel byte values.

> 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:,,
>            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 to 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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