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https://issues.apache.org/jira/browse/MAPREDUCE-5649?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14509866#comment-14509866
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Jason Lowe commented on MAPREDUCE-5649:
---------------------------------------
In general looks OK to me. Couple of nits:
We're taking a transient computation and storing it long-term apparently only
for unit testing purposes. I think we can unit test it in a way that doesn't
require long-term storage. We could allow createInMemorySegments to be
overridden in a derived test class so we could spy on the parameters to verify
the value comes out as expected.
This runtime exception message is not going to be very user-friendly. I
realize it did not originate with this patch, but since we're touching that
code it would be nice to clean it up a bit:
{code}
+ if (maxRedPer > 1.0 || maxRedPer < 0.0) {
+ throw new RuntimeException(MRJobConfig.REDUCE_INPUT_BUFFER_PERCENT +
+ maxRedPer);
+ }
{code}
> Reduce cannot use more than 2G memory for the final merge
> ----------------------------------------------------------
>
> Key: MAPREDUCE-5649
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-5649
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: mrv2
> Reporter: stanley shi
> Assignee: Gera Shegalov
> Attachments: MAPREDUCE-5649.001.patch
>
>
> In the org.apache.hadoop.mapreduce.task.reduce.MergeManagerImpl.java file, in
> the finalMerge method:
> int maxInMemReduce = (int)Math.min(
> Runtime.getRuntime().maxMemory() * maxRedPer, Integer.MAX_VALUE);
>
> This means no matter how much memory user has, reducer will not retain more
> than 2G data in memory before the reduce phase starts.
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