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https://issues.apache.org/jira/browse/SAMZA-353?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14121996#comment-14121996
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Martin Kleppmann commented on SAMZA-353:
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Good idea to move the shared state to SAMZA-402, I will look at it shortly.
bq. I agree hot standby seems desirable in the long run. I do question this
implementation style, though. It seems more elegant to simply implement a hot
standby by having it consume from the changelog and checkpoint topics for all
StreamTasks in a container. In such a case, you don't need to have
multi-subscriber streams.
I think I understand the hot standby implementation style you're describing.
I've tried to elaborate on it in SAMZA-406 — could you check whether I've got
it right, and correct me if necessary?
After pondering a while, I agree that the SAMZA-406 implementation style of hot
standby is preferable. In that case, I can't see a compelling use case for
multi-subscriber streams either.
My revised opinion is then: we should do shared state as discussed in
SAMZA-402, do hot standby as discussed in SAMZA-406, and *not* do
multi-subscriber streams (i.e. leave the current restriction in place) — unless
someone in future comes up with a compelling use case. I'm happy for this issue
to be closed as "won't fix".
> Support assigning the same SSP to multiple tasknames
> ----------------------------------------------------
>
> Key: SAMZA-353
> URL: https://issues.apache.org/jira/browse/SAMZA-353
> Project: Samza
> Issue Type: Bug
> Components: container
> Affects Versions: 0.8.0
> Reporter: Jakob Homan
> Attachments: DESIGN-SAMZA-353-0.md, DESIGN-SAMZA-353-0.pdf
>
>
> Post SAMZA-123, it is possible to add the same SSP to multiple tasknames,
> although currently we check for this and error out if this is done. We
> should think through the implications of having the same SSP appear in
> multiple tasknames and support this if it makes sense.
> This could be used as a broadcast stream that's either added by Samza itself
> to each taskname, or individual groupers could do this as makes sense. Right
> now the container maintains a map of SSP to TaskInstance and delivers the ssp
> to that task instance. With this change, we'd need to change the map to SSP
> to Set[TaskInstance] and deliver the message to each TI in the set.
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