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Posted to jira@kafka.apache.org by "Nikolay Izhikov (JIRA)" <ji...@apache.org> on 2018/11/01 11:55:00 UTC

[jira] [Commented] (KAFKA-7420) Global stores should be guarded as read-only for regular tasks

    [ https://issues.apache.org/jira/browse/KAFKA-7420?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16671503#comment-16671503 ] 

Nikolay Izhikov commented on KAFKA-7420:
----------------------------------------

[~mjsax]

> Does this help?

Yes, thanks. I'll try to provide PR in the next few days.

> Global stores should be guarded as read-only for regular tasks
> --------------------------------------------------------------
>
>                 Key: KAFKA-7420
>                 URL: https://issues.apache.org/jira/browse/KAFKA-7420
>             Project: Kafka
>          Issue Type: Improvement
>          Components: streams
>            Reporter: Matthias J. Sax
>            Assignee: Nikolay Izhikov
>            Priority: Minor
>              Labels: newbie++
>
> Global stores should only be update by the global thread. Any other task, should only read from a global store. However, when getting a reference to a global store, all tasks have full read/write access to the store.
> We should put a guard in place and only return either _(a)_ a read-only store, or _(b)_ wrap the store but throw an exception on write for regular tasks.
> While the read-only store idea might be cleaner from an API point of view, we should consider the second approach for 2 reasons: (1) it's backwards compatible (of course, code might fail at runtime, but this seems to be ok, as it indicates a bug in the user code anyway) (2) with regard to [KIP-358|https://cwiki.apache.org/confluence/display/KAFKA/KIP-358%3A+Migrate+Streams+API+to+Duration+instead+of+long+ms+times], we should have the more runtime efficient methods at this level (currently, global stores are only key-value stores and this argument falls a little short though—however, it might be a good idea to stay future proof; at least, we should discuss it).



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