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https://issues.apache.org/jira/browse/GEARPUMP-249?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15797144#comment-15797144
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ASF GitHub Bot commented on GEARPUMP-249:
-----------------------------------------
Github user manuzhang commented on the issue:
https://github.com/apache/incubator-gearpump/pull/127
R: @huafengw
> reduce is not executed when following flatMap in Stream DSL
> -----------------------------------------------------------
>
> Key: GEARPUMP-249
> URL: https://issues.apache.org/jira/browse/GEARPUMP-249
> Project: Apache Gearpump
> Issue Type: Bug
> Components: streaming
> Affects Versions: 0.8.2
> Reporter: Manu Zhang
> Assignee: Manu Zhang
> Fix For: 0.8.3
>
>
> The issue can be reproduced if a redundant {{map}} is added between
> {{groupBy}} and {{sum}}
> {code}
> app.source(data.lines.toList, 1, "source").
> // word => (word, count)
> flatMap(line => line.split("[\\s]+")).map((_, 1)).
> // (word, count1), (word, count2) => (word, count1 + count2)
> groupByKey().sum.log
> {code}
> The problem is with {{AndThen#process}} method, where {{flatMap}} is lazily/
> never executed.
> {code}
> override def process(value: IN): TraversableOnce[OUT] = {
> first.process(value).flatMap(second.process)
> }
> {code}
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