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https://issues.apache.org/jira/browse/HADOOP-492?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12477027
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David Bowen commented on HADOOP-492:
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> 1) Why does the method to increment a counter take an enum whereas the method
> to read the value takes a String?
> Wouldn't it be more convenient if Counters.getCounter() also took an enum?
Yes it would. The issue is that Counters objects move between processes,
including back to the client. I don't think we can safely assume that the
right Enum type will be available everywhere.
FYI I've changed the Counters API in a patch attached to Hadoop-1041, but it
isn't any simpler :-(. Counters are now grouped by the enum type that they
came from.
With regard to your test, it could be a bug. It would be interesting to see if
you get a similar discrepancy after applying the 1041 patch.
> Global counters
> ---------------
>
> Key: HADOOP-492
> URL: https://issues.apache.org/jira/browse/HADOOP-492
> Project: Hadoop
> Issue Type: New Feature
> Components: mapred
> Reporter: arkady borkovsky
> Assigned To: David Bowen
> Fix For: 0.12.0
>
> Attachments: counters1.patch, counters2.patch, counters3.patch
>
>
> It would be nice to have map / reduce job keep aggregated counts for
> arbitrary events occuring in its tasks -- the numer of records processed, the
> numer of exceptions of a specific type, the number of sentences in passive
> voice, whatever the jobs finds useful.
> This can be implemented by tasks periodically sending <name, value> pairs to
> the jobtracker (in some implementations such messages are piggy-backed on the
> heartbeats), so that the job tracker stores all the latests values from each
> task and aggregates them on a request. It should also make the aggregated
> values available at the job end. The value for a task would be flushed when
> the task fails.
> #491 and #490 may be related to this one.
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