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https://issues.apache.org/jira/browse/KAFKA-12845?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17352870#comment-17352870
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Matthias J. Sax commented on KAFKA-12845:
-----------------------------------------
Ah. I see what you are saying. Sorry that I misunderstood you original
description.
The change you point out was on purpose thought, because we do the same thing
for all other joins (ie, we consider it a bug-fix to bring stream-globalTable
join on par with other joins). The join key cannot be null and is treated as
invalid data.
I agree though, that for a _left_ join, it might make sense to all the key to
be null and to produce a left-join result for this case (cf
https://issues.apache.org/jira/browse/KAFKA-12317). If we do this, we should do
it for both joins though, not just stream-globalTable.
As it seems that we are both on the same page, I think we can close this ticket
as a duplicate to K12317 ?
> Rollback change which requires join key to be non null on
> KStream->GlobalKTable
> -------------------------------------------------------------------------------
>
> Key: KAFKA-12845
> URL: https://issues.apache.org/jira/browse/KAFKA-12845
> Project: Kafka
> Issue Type: Improvement
> Components: streams
> Affects Versions: 2.7.0
> Reporter: Pedro Gontijo
> Priority: Major
>
> As part of [KAFKA-10277|https://issues.apache.org/jira/browse/KAFKA-10277]
> the behavior for KStream->GlobalKtable joins was changed to require non null
> join keys.
> But it seems reasonable that not every record will have an existing
> relationship (and hence a key) with the join globalktable. Think about a
> User>Car for instance, or PageView>Product. An empty/zero key could be
> returned by the KeyMapper but that will make a totally unnecessary search
> into the store.
> I do not think that makes sense for any GlobalKtable join (inner or left) but
> for left join it sounds even more strange.
>
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