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https://issues.apache.org/jira/browse/KAFKA-1430?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14069171#comment-14069171
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Guozhang Wang commented on KAFKA-1430:
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Updated reviewboard https://reviews.apache.org/r/23767/
against branch origin/trunk
> Purgatory redesign
> ------------------
>
> Key: KAFKA-1430
> URL: https://issues.apache.org/jira/browse/KAFKA-1430
> Project: Kafka
> Issue Type: Improvement
> Components: core
> Affects Versions: 0.8.2
> Reporter: Jun Rao
> Assignee: Guozhang Wang
> Attachments: KAFKA-1430.patch, KAFKA-1430.patch, KAFKA-1430.patch,
> KAFKA-1430.patch, KAFKA-1430.patch, KAFKA-1430_2014-06-05_17:07:37.patch,
> KAFKA-1430_2014-06-05_17:13:13.patch, KAFKA-1430_2014-06-05_17:40:53.patch,
> KAFKA-1430_2014-06-10_11:22:06.patch, KAFKA-1430_2014-06-10_11:26:02.patch,
> KAFKA-1430_2014-07-11_10:59:13.patch, KAFKA-1430_2014-07-21_12:53:39.patch
>
>
> We have seen 2 main issues with the Purgatory.
> 1. There is no atomic checkAndWatch functionality. So, a client typically
> first checks whether a request is satisfied or not and then register the
> watcher. However, by the time the watcher is registered, the registered item
> could already be satisfied. This item won't be satisfied until the next
> update happens or the delayed time expires, which means the watched item
> could be delayed.
> 2. FetchRequestPurgatory doesn't quite work. This is because the current
> design tries to incrementally maintain the accumulated bytes ready for fetch.
> However, this is difficult since the right time to check whether a fetch (for
> regular consumer) request is satisfied is when the high watermark moves. At
> that point, it's hard to figure out how many bytes we should incrementally
> add to each pending fetch request.
> The problem has been reported in KAFKA-1150 and KAFKA-703.
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