I test the HDFS pread performance, the avg time of pread is about 10ms, but pread max time reach 200ms, there is about one percent of pread time is 200ms, that result to my application is timeout.
I find max time of the RemoteBlockReader<eclipse-javadoc:%E2%98%82=hadoop-0.20.2-cdh3u5/src%5C/hdfs%3Corg.apache.hadoop.hdfs%7BDFSClient.java%E2%98%83DFSClient%E2%98%83RemoteBlockReader>.readChunk method also can reach 100ms. The RemoteBlockReader<eclipse-javadoc:%E2%98%82=hadoop-0.20.2-cdh3u5/src%5C/hdfs%3Corg.apache.hadoop.hdfs%7BDFSClient.java%E2%98%83DFSClient%E2%98%83RemoteBlockReader>.readChunk only read 512 bytes form socket, so I think I can tuning linux socket Kernel parameters to reduce the max time of pread. If anybody has the experience, please tell me. Thansk, LiuLei
