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https://issues.apache.org/jira/browse/HADOOP-1170?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12484967
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dhruba borthakur commented on HADOOP-1170:
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I like the idea of a background thread that periodically checks the data
directories. The idea is to detect bad/inaccessible data directories and
shutdown the datanode if this occurs, right?
> Very high CPU usage on data nodes because of FSDataset.checkDataDir() on
> every connect
> --------------------------------------------------------------------------------------
>
> Key: HADOOP-1170
> URL: https://issues.apache.org/jira/browse/HADOOP-1170
> Project: Hadoop
> Issue Type: Bug
> Components: dfs
> Affects Versions: 0.11.2
> Reporter: Igor Bolotin
> Attachments: 1170.patch
>
>
> While investigating performance issues in our Hadoop DFS/MapReduce cluster I
> saw very high CPU usage by DataNode processes.
> Stack trace showed following on most of the data nodes:
> "[EMAIL PROTECTED]" daemon prio=1 tid=0x00002aaacb5b7bd0 nid=0x5940 runnable
> [0x000000004166a000..0x000000004166ac00]
> at java.io.UnixFileSystem.checkAccess(Native Method)
> at java.io.File.canRead(File.java:660)
> at org.apache.hadoop.util.DiskChecker.checkDir(DiskChecker.java:34)
> at
> org.apache.hadoop.dfs.FSDataset$FSDir.checkDirTree(FSDataset.java:164)
> at
> org.apache.hadoop.dfs.FSDataset$FSDir.checkDirTree(FSDataset.java:168)
> at
> org.apache.hadoop.dfs.FSDataset$FSDir.checkDirTree(FSDataset.java:168)
> at
> org.apache.hadoop.dfs.FSDataset$FSDir.checkDirTree(FSDataset.java:168)
> at
> org.apache.hadoop.dfs.FSDataset$FSDir.checkDirTree(FSDataset.java:168)
> at
> org.apache.hadoop.dfs.FSDataset$FSDir.checkDirTree(FSDataset.java:168)
> at
> org.apache.hadoop.dfs.FSDataset$FSDir.checkDirTree(FSDataset.java:168)
> at
> org.apache.hadoop.dfs.FSDataset$FSDir.checkDirTree(FSDataset.java:168)
> at
> org.apache.hadoop.dfs.FSDataset$FSDir.checkDirTree(FSDataset.java:168)
> at
> org.apache.hadoop.dfs.FSDataset$FSDir.checkDirTree(FSDataset.java:168)
> at
> org.apache.hadoop.dfs.FSDataset$FSDir.checkDirTree(FSDataset.java:168)
> at
> org.apache.hadoop.dfs.FSDataset$FSDir.checkDirTree(FSDataset.java:168)
> at
> org.apache.hadoop.dfs.FSDataset$FSDir.checkDirTree(FSDataset.java:168)
> at
> org.apache.hadoop.dfs.FSDataset$FSDir.checkDirTree(FSDataset.java:168)
> at
> org.apache.hadoop.dfs.FSDataset$FSVolume.checkDirs(FSDataset.java:258)
> at
> org.apache.hadoop.dfs.FSDataset$FSVolumeSet.checkDirs(FSDataset.java:339)
> - locked <0x00002aaab6fb8960> (a
> org.apache.hadoop.dfs.FSDataset$FSVolumeSet)
> at org.apache.hadoop.dfs.FSDataset.checkDataDir(FSDataset.java:544)
> at
> org.apache.hadoop.dfs.DataNode$DataXceiveServer.run(DataNode.java:535)
> at java.lang.Thread.run(Thread.java:595)
> I understand that it would take a while to check the entire data directory -
> as we have some 180,000 blocks/files in there. But what really bothers me
> that from the code I see that this check is executed for every client
> connection to the DataNode - which also means for every task executed in the
> cluster. Once I commented out the check and restarted datanodes - the
> performance went up and CPU usage went down to reasonable level.
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