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From "James Cheng (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (KAFKA-4113) Allow KTable bootstrap
Date Thu, 01 Sep 2016 22:52:20 GMT

    [ https://issues.apache.org/jira/browse/KAFKA-4113?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15456866#comment-15456866

James Cheng commented on KAFKA-4113:

I wrote a blog post on some other ways to know when you have read everything in a Kafka topic:

> Allow KTable bootstrap
> ----------------------
>                 Key: KAFKA-4113
>                 URL: https://issues.apache.org/jira/browse/KAFKA-4113
>             Project: Kafka
>          Issue Type: Sub-task
>          Components: streams
>            Reporter: Matthias J. Sax
>            Assignee: Guozhang Wang
> On the mailing list, there are multiple request about the possibility to "fully populate"
a KTable before actual stream processing start.
> Even if it is somewhat difficult to define, when the initial populating phase should
end, there are multiple possibilities:
> The main idea is, that there is a rarely updated topic that contains the data. Only after
this topic got read completely and the KTable is ready, the application should start processing.
This would indicate, that on startup, the current partition sizes must be fetched and stored,
and after KTable got populated up to those offsets, stream processing can start.
> Other discussed ideas are:
> 1) an initial fixed time period for populating
> (it might be hard for a user to estimate the correct value)
> 2) an "idle" period, ie, if no update to a KTable for a certain time is
> done, we consider it as populated
> 3) a timestamp cut off point, ie, all records with an older timestamp
> belong to the initial populating phase
> The API change is not decided yet, and the API desing is part of this JIRA.
> One suggestion (for option (4)) was:
> {noformat}
> KTable table = builder.table("topic", 1000); // populate the table without reading any
other topics until see one record with timestamp 1000.
> {noformat}

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