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https://issues.apache.org/jira/browse/GEARPUMP-32?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15430069#comment-15430069
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ASF GitHub Bot commented on GEARPUMP-32:
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Github user asfgit closed the pull request at:
https://github.com/apache/incubator-gearpump/pull/67
> Minimum clock of source Tasks maybe inaccurate
> ----------------------------------------------
>
> Key: GEARPUMP-32
> URL: https://issues.apache.org/jira/browse/GEARPUMP-32
> Project: Apache Gearpump
> Issue Type: Bug
> Components: streaming
> Affects Versions: 0.8.0
> Reporter: Manu Zhang
> Assignee: Manu Zhang
> Fix For: 0.8.2
>
>
> Moved from [https://github.com/gearpump/gearpump/issues/1835] and reported by
> [Zhu Yueqian|https://github.com/yueqianzhu]
> {quote}
> Source tasks have not any upstreamClocks. So, startClock is the minimum of
> pending clocks when recover happen.
> eg below:
> source task1: timeStamp:15,not ACK, minClockValue maybe is 15(<= 15).
> source task2: timeStamp:10,ACKed, minClockValue maybe is Long.MaxValue
> when recover happen,startClock maybe is 15. where is the data between 10 to
> 15 at task2?
> {quote}
> More context on this issue:
> In Gearpump, we maintain a global minimum clock tracked from a message's
> timestamp across all tasks. It means messages with timestamp before this
> clock have all been processed. An application will restart from this value on
> failure, and thus at-least-once message delivery could be guaranteed.
> The global minimum clock is the lower bound of all the Tasks' minimum clocks.
> For a task, the minimum clock is the lower of
> # upstream minimum clock
> # a. the minimum timestamp of unacked messages
> b. Long.MaxValue if all messages have been acked.
>
> Note that 2.b allows the global minimum clock to progress and it is almost
> safe since the clock is also bounded by the upstream minimum clock. I said
> "almost safe" because a source task has no upstream but we assume the
> upstream minimum clock is Long.MaxValue. Thus, the scenario described by Zhu
> Yueqian could happen and breaks at-least-once guarantee.
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