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From "Igor Bolotin (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-1170) Very high CPU usage on data nodes because of FSDataset.checkDataDir() on every connect
Date Fri, 30 Mar 2007 19:58:25 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-1170?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Igor Bolotin updated HADOOP-1170:
---------------------------------

    Status: Patch Available  (was: Open)

> 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-v2.patch, 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:
> "org.apache.hadoop.dfs.DataNode$DataXceiveServer@528acf6e" daemon prio=1 tid=0x00002aaacb5b7bd0
nid=0x5940 runnable [0x000000004166a000..0x000000004166ac00]
>         at java.io.UnixFileSystem.checkAccess(Native Method)
>         at java.io.File.canRead(File.java:660)
>         at org.apache.hadoop.util.DiskChecker.checkDir(DiskChecker.java:34)
>         at org.apache.hadoop.dfs.FSDataset$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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