一 问题
Dubbo monitor所在服务器状态异常，iowait一直很高，load也一直很高，监控如下：
iowait如图：
load如图：
二 分析
通过iotop命令可以查看当前系统中磁盘io情况以及进程占用磁盘io的情况
从中可以定位到占用io进程的pid；
通过cat /proc/${pid}/io 可以查看一个进程具体的读写状况；
通过 ps aux|grep ${pid} 可以查到这个进程具体的命令；
通过以上命令定位到进程为dubbo的monitor进程，用jstack打印线程栈发现处于RUNNABLE的进程除了
java.lang.Thread.State: RUNNABLE
at sun.nio.ch.EPollArrayWrapper.epollWait(Native Method)
之外，有两个线程很可疑
"DubboMonitorTimer-thread-1" daemon prio=10 tid=0x00007f53b0593000 nid=0x363e runnable [0x00007f53ac36d000]
java.lang.Thread.State: RUNNABLE
at java.io.FileInputStream.readBytes(Native Method)
at java.io.FileInputStream.read(FileInputStream.java:272)
at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:283)
at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:325)
at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:177)
- locked <0x0000000779d506f8> (a java.io.FileReader)
at java.io.InputStreamReader.read(InputStreamReader.java:184)
at java.io.BufferedReader.fill(BufferedReader.java:154)
at java.io.BufferedReader.readLine(BufferedReader.java:317)
- locked <0x0000000779d506f8> (a java.io.FileReader)
at java.io.BufferedReader.readLine(BufferedReader.java:382)
at com.alibaba.dubbo.monitor.simple.SimpleMonitorService.appendData(SimpleMonitorService.java:322)
at com.alibaba.dubbo.monitor.simple.SimpleMonitorService.draw(SimpleMonitorService.java:263)
at com.alibaba.dubbo.monitor.simple.SimpleMonitorService.access$300(SimpleMonitorService.java:64)
at com.alibaba.dubbo.monitor.simple.SimpleMonitorService$2.run(SimpleMonitorService.java:137)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:304)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:178)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:744)
Locked ownable synchronizers:
- <0x0000000788104268> (a java.util.concurrent.ThreadPoolExecutor$Worker)
"DubboMonitorAsyncWriteLogThread" daemon prio=10 tid=0x00007f53b05ba000 nid=0x363d runnable [0x00007f53ac3af000]
java.lang.Thread.State: RUNNABLE
at java.io.FileOutputStream.writeBytes(Native Method)
at java.io.FileOutputStream.write(FileOutputStream.java:345)
at sun.nio.cs.StreamEncoder.writeBytes(StreamEncoder.java:221)
at sun.nio.cs.StreamEncoder.implFlushBuffer(StreamEncoder.java:291)
at sun.nio.cs.StreamEncoder.implFlush(StreamEncoder.java:295)
at sun.nio.cs.StreamEncoder.flush(StreamEncoder.java:141)
- locked <0x000000077a028918> (a java.io.FileWriter)
at java.io.OutputStreamWriter.flush(OutputStreamWriter.java:229)
at com.alibaba.dubbo.monitor.simple.SimpleMonitorService.write(SimpleMonitorService.java:213)
at com.alibaba.dubbo.monitor.simple.SimpleMonitorService.access$100(SimpleMonitorService.java:64)
at com.alibaba.dubbo.monitor.simple.SimpleMonitorService$1.run(SimpleMonitorService.java:120)
at java.lang.Thread.run(Thread.java:744)
Locked ownable synchronizers:
- None
这两个线程一个在read，一个在write，查看dubbo monitor的源代码发现：
monitor中会有两个线程，一个不停地写统计日志，一个每隔300s进行一次draw操作；
monitor中每天的日志都会保存在一个日志目录中，进入其中一天的日志目录查看日志大小：
发现一天的日志只有几十M，而上边iotop查看的结果是read是1520K/s,write是3.43M/s，所以排除write的问题，问题应该出在draw身上，查看draw的源代码发现draw会不断的读取统计日志同时进行绘图操作，
draw中会遍历日志目录，同时在appendData方法中会进行日志读取操作，由于monitor已经运行很长时间，所以按天保存的目录非常多，每次draw都需要去遍历这些目录并且进行读取文件操作，历史数据没有改动但却会不断的重新进行日志读取和绘图，问题应该出在这里；
三 解决
修改代码如下
即让draw只对当天的日志进行处理，修改之后服务器iowait如图：
load如图：
问题解决