Maximum Number of File Handles Is Set to a Too Small Value, Causing File Reading and Writing Exceptions

Symptom

The maximum number of file handles is set to a too small value, causing insufficient file handles. Writing files to HDFS is slow or file writing fails.

Cause Analysis

1. The DataNode log /var/log/Bigdata/hdfs/dn/hadoop-omm-datanode-XXX.log contains exception information "java.io.IOException: Too many open files."

   2016-05-19 17:18:59,126 | WARN  | org.apache.hadoop.hdfs.server.datanode.DataXceiverServer@142ff9fa | YSDN12:25009:DataXceiverServer:  | org.apache.hadoop.hdfs.server.datanode.DataXceiverServer.run(DataXceiverServer.java:160)
   java.io.IOException: Too many open files
   at sun.nio.ch.ServerSocketChannelImpl.accept0(Native Method)
   at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:241)
   at sun.nio.ch.ServerSocketAdaptor.accept(ServerSocketAdaptor.java:100)
   at org.apache.hadoop.hdfs.net.TcpPeerServer.accept(TcpPeerServer.java:134)
   at org.apache.hadoop.hdfs.server.datanode.DataXceiverServer.run(DataXceiverServer.java:137)
   at java.lang.Thread.run(Thread.java:745)

2. The error indicates insufficient file handles. File handles cannot be opened and data is written to other DataNodes. As a result, writing files is slow or fails.

Solution

1. Run the ulimit -a command to check the maximum number of file handles set for the involved node. If the value is small, change it to 640000.
   Figure 1 Check the number of file handles.
   

2. Run the vi /etc/security/limits.d/90-nofile.conf command to edit this file. Set the number of file handles to 64000. If the file does not exist, create one and modify the file as follows:
   Figure 2 Changing the number of file handles
   

3. Open another terminal. Run the ulimit -a command to check whether the modification is successful. If the modification fails, perform the preceding operations again.
4. Restart the DataNode instance on Manager.