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https://issues.apache.org/jira/browse/HADOOP-3398?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12597350#action_12597350
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Amar Kamat commented on HADOOP-3398:
------------------------------------
Code looks fine. The values are same for both the implementations. Some
comments as to what is done could be useful. I compared the two implementations
||input||num-iterations||before (milli)||after (milli)||
|10000|1000000|642|19|
|5000|1000000|78|9|
|2500|1000000|74|5|
|1000|1000000|69|3|
|500|1000000|51|1|
|300|1000000|49|1|
Assuming that the map runtime can vary from 300sec to 10,000 secs and the
maximum number of times {{getClosestPowerOf2()}} will be invoked is 1,000,000.
> ReduceTask::closestPowerOf2 is inefficient
> ------------------------------------------
>
> Key: HADOOP-3398
> URL: https://issues.apache.org/jira/browse/HADOOP-3398
> Project: Hadoop Core
> Issue Type: Bug
> Components: mapred
> Reporter: Chris Douglas
> Assignee: Chris Douglas
> Priority: Trivial
> Fix For: 0.18.0
>
> Attachments: 3398-0.patch, 3398-1.patch
>
>
> ReduceTask computes the "closest power of 2" using loops
> {code}
> private static int getClosestPowerOf2(int value) {
> int power = 0;
> int approx = 1;
> while (approx < value) {
> ++power;
> approx = (approx << 1);
> }
> if ((value - (approx >> 1)) < (approx - value)) {
> --power;
> }
> return power;
> }
> {code}
> This could be improved.
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