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https://issues.apache.org/jira/browse/MAPREDUCE-1374?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12799930#action_12799930
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dhruba borthakur commented on MAPREDUCE-1374:
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+1 for this patch.
> is this same behavior observed elsewhere in HDFS that duplicate
The HDFS servers stores path names as strings and UTF byte arrays but there
should not be too many duplicate entries in these, isn't it?
> Reduce memory footprint of FileSplit
> ------------------------------------
>
> Key: MAPREDUCE-1374
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-1374
> Project: Hadoop Map/Reduce
> Issue Type: Improvement
> Affects Versions: 0.20.1, 0.21.0, 0.22.0
> Reporter: Zheng Shao
> Assignee: Zheng Shao
> Fix For: 0.21.0, 0.22.0
>
> Attachments: MAPREDUCE-1374.1.patch, MAPREDUCE-1374.2.patch,
> MAPREDUCE-1374.3.patch
>
>
> We can have many FileInput objects in the memory, depending on the number of
> mappers.
> It will save tons of memory on JobTracker and JobClient if we intern those
> Strings for host names.
> {code}
> FileInputFormat.java:
> for (NodeInfo host: hostList) {
> // Strip out the port number from the host name
> - retVal[index++] = host.node.getName().split(":")[0];
> + retVal[index++] = host.node.getName().split(":")[0].intern();
> if (index == replicationFactor) {
> done = true;
> break;
> }
> }
> {code}
> More on String.intern():
> http://www.javaworld.com/javaworld/javaqa/2003-12/01-qa-1212-intern.html
> It will also save a lot of memory by changing the class of {{file}} from
> {{Path}} to {{String}}. {{Path}} contains a {{java.net.URI}} which internally
> contains ~10 String fields. This will also be a huge saving.
> {code}
> private Path file;
> {code}
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