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https://issues.apache.org/jira/browse/NUTCH-2328?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15586425#comment-15586425
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Arthur B commented on NUTCH-2328:
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I don't think this has anything to do with Spring/Hadoop: it just recreates the
issue. I believe you can recreate this from a standalone app that will submit
the GeneratorJob twice to Hadoop (I recon we can disregard that aspect - Spring
Data Hadoop).
Regarding the locality of the {{count}} variable: I do not believe that turning
it into a {{instance}} member would do here, unless I am missing something I do
not think that it will be solving the issue. My reasoning for this is that a
{{GeneratorJob}} once submitted to Hadoop, you can not count on the fact that
it will only reside on one Hadoop node. Potentially the {{M/R job}} will run in
multiple Hadoop nodes, and the {{M/R job}} should not have state as such (you
can not count on its locality). So in my opinion the only solution is to have a
cluster wide propagated {{count}}er that keeps track of how many {{Webpage}}s
have been dealt with.
AFAIK a local class {{instance}} variable would not do this (propagate a
cluster wide counter)... unless I am missing something. It can be easily tested
by running it on a 2 cluster machine and letting more than one Reducers run up.
> GeneratorJob does not generate anything on second run
> -----------------------------------------------------
>
> Key: NUTCH-2328
> URL: https://issues.apache.org/jira/browse/NUTCH-2328
> Project: Nutch
> Issue Type: Bug
> Components: generator
> Affects Versions: 2.2, 2.3, 2.2.1, 2.3.1
> Environment: Ubuntu 16.04 / Hadoop 2.7.1
> Reporter: Arthur B
> Labels: fails, generator, subsequent
> Fix For: 2.4
>
> Attachments: generator-issue-static-count.patch
>
> Original Estimate: 24h
> Remaining Estimate: 24h
>
> Given a topN parameter (ie 10) the GeneratorJob will fail to generate
> anything new on the subsequent runs within the same process space.
> To reproduce the issue submit the GeneratorJob twice one after another to the
> M/R framework. Second time will say it generated 0 URLs.
> This issue is due to the usage of the static count field
> (org.apache.nutch.crawl.GeneratorReducer#count) to determine if the topN
> value has been reached.
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