[
https://issues.apache.org/jira/browse/NUTCH-2328?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15588759#comment-15588759
]
Sebastian Nagel commented on NUTCH-2328:
----------------------------------------
Hi [~arthur-evozon],
> Btw., I'm even not sure whether counters in the task context are updated with
> global job values.
The answer is: counters in task context *do not show aggregated values* over
all tasks of a job.
That's more or less clear from these definitions: "Counter is a facility for
MapReduce applications to report its statistics."
[[1|https://hadoop.apache.org/docs/stable/hadoop-mapreduce-client/hadoop-mapreduce-client-core/MapReduceTutorial.html#Counter]],
more details in Tom White's "Hadoop, the definitive guide". Counter values are
propagated and aggregated in this direction: task > task tracker > job tracker
> job client. The aggregated values are not sent back. There are hacks to
access the aggregated values from the tasks, cf.
[[2|http://stackoverflow.com/questions/8009802/is-there-a-way-to-access-number-of-successful-map-tasks-from-a-reduce-task-in-an/8013573#8013573]].
But the central problem persists: the value of a job counter depends mostly on
how many tasks are in progress or already done. If the programming logic relies
on such a value it becomes largely indeterministic.
> 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.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
