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Posted to common-dev@hadoop.apache.org by "dhruba borthakur (JIRA)" <ji...@apache.org> on 2007/04/19 20:28:15 UTC
[jira] Commented: (HADOOP-1170) Very high CPU usage on data nodes
because of FSDataset.checkDataDir() on every connect
[ https://issues.apache.org/jira/browse/HADOOP-1170?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12490129 ]
dhruba borthakur commented on HADOOP-1170:
------------------------------------------
This patch improves the performance situation but removes all checkDirs from the datanode. This introduces the problem that disk's migt not get checked for a long time. This is dangerous for a cluster where disks go bad. I think we should either implement a background thread to call checkDirs() before this patch can be deployed on a real cluster.
> 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
> Fix For: 0.13.0
>
> 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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