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 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. -- This message is automatically generated by JIRA. - You can reply to this email to add a comment to the issue online.