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https://issues.apache.org/jira/browse/HADOOP-2774?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12649304#action_12649304
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Chris Douglas commented on HADOOP-2774:
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(1) IFile is a package-private class, no? If it's not visible outside of the
mapred package, using other components in that package doesn't seem like
pollution to me. If the class responsible for emitting records counts the
number of records it emits using the class responsible for counting, that seems
like a victory for reuse and coherence. Is there a particular reason the two
should be kept separate? Indiscriminate coupling of unrelated components is to
be avoided, certainly, but this strikes me as a plain win.
(2) Just to make sure I understand: the proposal is to add a new interface,
IFileDiskOperationsMonitor, which Task would implement. The Task would pass a
reference to itself (or an inner class would pass a reference to its containing
instance) to the IFile.\{Reader,Writer\} instance, which would hold that
reference until it closes, when it would pass its internal count to the
IFileDiskOperations instance, which would update the counter. Is that correct?
* Why the indirection? Why create a new type for monitoring disk operations
passing through a particular, intermediate format, a format already limited to
a package that already contains a type that implements a superset of the new
type's functionality?
* Task should not gain a new interface each time we want to track a new
quantity or type of quantity. Further, the IFile format is not part of the Task
type. Metrics from the IFile format certainly are not.
* If the issue is performance, there's no reason why the counter can't be
updated in the same way.
* Passing a named counter in some contexts is far more readable than passing
\*Task.this in some contexts, but not in others.
bq. This seems fairly generic and in the future could be used by any other
potential user of Ifile/Merger classes (outside MapReduce)
And yet it is emphatically less generic than the Counters, which already
provide an interface to consumers outside the mapred package.
> Add counters to show number of key/values that have been sorted and merged in
> the maps and reduces
> --------------------------------------------------------------------------------------------------
>
> Key: HADOOP-2774
> URL: https://issues.apache.org/jira/browse/HADOOP-2774
> Project: Hadoop Core
> Issue Type: Bug
> Reporter: Owen O'Malley
> Assignee: Ravi Gummadi
> Fix For: 0.20.0
>
> Attachments: HADOOP-2774.patch, HADOOP-2774.patch
>
>
> For each *pass* of the sort and merge, I would like a count of the number of
> records. So for example, if the map output 100 records and they were sorted
> once, the counter would be 100. If it spilled twice and was merged together,
> it would be 200. Clearly in a multi-level merge, it may not be a multiple of
> the number of map output records. This would let the users easily see if they
> have values like io.sort.mb or io.sort.factor set too low.
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