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https://issues.apache.org/jira/browse/HADOOP-4780?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12689398#action_12689398
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Zheng Shao commented on HADOOP-4780:
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Yes. The original code was correct, but just too slow.
The new code is much faster especially when the local cache contains a lot of
directories.
I changed it from a bug to an improvement.
The test is a functionality test.
As a side note, we've used this patch internally on 0.17 for some time now. The
long delay of starting new tasks (sometimes over 3 minutes) has disappeared
while the number of jobs on our job tracker (since restart) has exceeded 80000
now.
> Task Tracker burns a lot of cpu in calling getLocalCache
> ---------------------------------------------------------
>
> Key: HADOOP-4780
> URL: https://issues.apache.org/jira/browse/HADOOP-4780
> Project: Hadoop Core
> Issue Type: Improvement
> Components: mapred
> Affects Versions: 0.19.0
> Reporter: Runping Qi
> Assignee: He Yongqiang
> Fix For: 0.19.2
>
> Attachments: Hadoop-4780-2.patch
>
>
> I noticed that many times, a task tracker max up to 6 cpus.
> During that time, iostat shows majority of that was system cpu.
> That situation can last for quite long.
> During that time, I saw a number of threads were in the following state:
> java.lang.Thread.State: RUNNABLE
> at java.io.UnixFileSystem.getBooleanAttributes0(Native Method)
> at
> java.io.UnixFileSystem.getBooleanAttributes(UnixFileSystem.java:228)
> at java.io.File.exists(File.java:733)
> at org.apache.hadoop.fs.FileUtil.getDU(FileUtil.java:399)
> at org.apache.hadoop.fs.FileUtil.getDU(FileUtil.java:407)
> at org.apache.hadoop.fs.FileUtil.getDU(FileUtil.java:407)
> at org.apache.hadoop.fs.FileUtil.getDU(FileUtil.java:407)
> at org.apache.hadoop.fs.FileUtil.getDU(FileUtil.java:407)
> at org.apache.hadoop.fs.FileUtil.getDU(FileUtil.java:407)
> at org.apache.hadoop.fs.FileUtil.getDU(FileUtil.java:407)
> at org.apache.hadoop.fs.FileUtil.getDU(FileUtil.java:407)
> at org.apache.hadoop.fs.FileUtil.getDU(FileUtil.java:407)
> at org.apache.hadoop.fs.FileUtil.getDU(FileUtil.java:407)
> at org.apache.hadoop.fs.FileUtil.getDU(FileUtil.java:407)
> at org.apache.hadoop.fs.FileUtil.getDU(FileUtil.java:407)
> at org.apache.hadoop.fs.FileUtil.getDU(FileUtil.java:407)
> at org.apache.hadoop.fs.FileUtil.getDU(FileUtil.java:407)
> at
> org.apache.hadoop.filecache.DistributedCache.getLocalCache(DistributedCache.java:176)
> at org.apache.hadoop.mapred.TaskRunner.run(TaskRunner.java:140)
> I suspect that getLocalCache is too expensive.
> And calling it for every task initialization seems too much waste.
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