iotop&iostat （load高 IO高的问题排查）

目标：使用iotop&top&jstack命令定位 io高的应用以及线程信息

实现：load过高但是cpu占用率低的模拟与验证

一般load高，说明系统大量的线程在等待执行

cpu  us sy 显示都不高，并且wa 占用高，说明系统在等待大量的io操作

 

1、安装iotop

sudo yum install iotop

 

2、top命令显示

 

从top命令可以看出，系统load 6.43，对于4 cpu的系统来说，已经是超载，另外 wa 60%，可以确定系统的线程在等待io操作

其中 线程 2492 比较可疑

top -H -p 2492

 

 

3、iostat

iostat ALL ：可以查阅 那个磁盘读写频繁

4、sudo iotop

可以查看哪些线程在 做读写io

 

 

 FileReadWrite 应用：三个线程，每个线程都在每秒36M，42M，75M的速度读写io

试验测试代码为：

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;

public class FileReadWrite {
        public static void main(String[] args) {
                for(int i =0;i<4;i++){
                        new T().start();
                }
        }
        
        
        public static class T extends Thread{
                @Override
                public void run() {
                        while (true){
                                try {
                                        exec();
                                } catch (Exception e) {
                                        e.printStackTrace();
                                }
                        }
                }
        }
        
        
        private static void exec() throws Exception{
                long start = System.currentTimeMillis();
                String fileName = "A"+System.currentTimeMillis();
                File f = new File(fileName);
                if(!f.exists()){
                        System.out.println(fileName + " created ");
                        f.createNewFile();
                }
                FileOutputStream fi = new FileOutputStream(f);
                
                int i = 0;
                while(true){
                        i++;
                        byte[] data = new byte[1024*1024*5];
                        fi.write(data);
                        if(i>50){
                                break;
                        }
                }
                fi.close();
                FileInputStream f2 =  new FileInputStream(f);
                
                byte[] data = new byte[1024*1024*1];
                int ret = f2.read(data);
                while(ret != -1){
                        data = new byte[1024*1024*1];
                        ret = f2.read(data);
                }
                boolean rt = f.delete();
                System.out.println(fileName + " deleted " + rt + "  time :" + (System.currentTimeMillis() - start));
        
        }
}

jstack 可以看大量的线程阻塞在了read 和write上：

"DestroyJavaVM" prio=10 tid=0x00007fabb4008800 nid=0x1774 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Thread-3" prio=10 tid=0x00007fabb40d6800 nid=0x1784 runnable [0x00007faba7af9000]
   java.lang.Thread.State: RUNNABLE
        at java.io.FileOutputStream.writeBytes(Native Method)
        at java.io.FileOutputStream.write(FileOutputStream.java:325)
        at FileReadWrite.exec(FileReadWrite.java:42)
        at FileReadWrite.access$000(FileReadWrite.java:6)
        at FileReadWrite$T.run(FileReadWrite.java:19)

"Thread-2" prio=10 tid=0x00007fabb40d4800 nid=0x1783 runnable [0x00007faba7bfa000]
   java.lang.Thread.State: RUNNABLE
        at java.io.FileInputStream.readBytes(Native Method)
        at java.io.FileInputStream.read(FileInputStream.java:243)
        at FileReadWrite.exec(FileReadWrite.java:54)
        at FileReadWrite.access$000(FileReadWrite.java:6)
        at FileReadWrite$T.run(FileReadWrite.java:19)

"Thread-1" prio=10 tid=0x00007fabb40d2800 nid=0x1782 runnable [0x00007faba7cfb000]
   java.lang.Thread.State: RUNNABLE
        at java.io.FileInputStream.readBytes(Native Method)
        at java.io.FileInputStream.read(FileInputStream.java:243)
        at FileReadWrite.exec(FileReadWrite.java:54)
        at FileReadWrite.access$000(FileReadWrite.java:6)
        at FileReadWrite$T.run(FileReadWrite.java:19)

"Thread-0" prio=10 tid=0x00007fabb40d0800 nid=0x1781 waiting on condition [0x00007faba7dfc000]
   java.lang.Thread.State: RUNNABLE
        at FileReadWrite.exec(FileReadWrite.java:53)
        at FileReadWrite.access$000(FileReadWrite.java:6)
        at FileReadWrite$T.run(FileReadWrite.java:19)