• java性能分析


    背景

            有处理过生产问题的同学基本都能遇到系统忽然缓慢,CPU突然飙升,甚至整个应用请求不可用。当出现这种情况下,在不影响数据准确性的前提下,我们应该尽快导出jstack和内存信息,然后重启系统,尽快回复系统的可用性,避免用户体验过差。本文针对CPU飙升问题,提供该问题的排查思路,从而能够快速定位到某线程甚至某快代码导致CPU飙升,从而提供处理该问题的思路。

    排查过程

    1. 通过top命令查看cpu飙升的java进程pid
    2. 通过ps -mp [pid] -o THREAD,tid,time查看该进程下所拥有的线程及各个线程占用cpu的使用率,并且记录CPU使用率过高的线程ID号
    3. 将线程ID号转换为16进程的数值记为tid_hex
    4. 使用jdk自带jstack监控命令
    5. 使用命令jstack [pid] | grep tid_hex -A100命令输出该线程的堆栈信息
    6. 根据堆栈信息分析代码。

    通过以上步骤可以查找出导致cpu飙升的相关代码位置,然后对代码进行code review即可。

    工具封装

    1. 以上步骤已经封装为脚本文件,通过以下脚本文件只需要指定进程ID即pid即可导出默认前5条导致CPU率过高的堆栈信息。
    2. 已上传github : 点我进入
    ./java-thread-top.sh -p pid
    
    #!/bin/bash
    # @Function
    # Find out the highest cpu consumed threads of java processes, and print the stack of these threads.
    # @github https://github.com/cjunn/script_tool/
    # @author cjunn
    # @date Sun Jan 12 2020 21:08:58 GMT+0800
    #
    
    pid='';
    count=5;
    mode=0;
    function usage(){
    	readonly PROG="`basename $0`"
    	cat <<EOF
    Usage: ${PROG} [OPTION]
    Find out the highest cpu consumed threads of java processes,
    and print the stack of these threads.
    Example:
      ${PROG} -p <pid> -c 5      # show top 5 busy java threads info
    Output control:
      -p, --pid <java pid>      find out the highest cpu consumed threads from
                                the specified java process.
                                default from all java process.
      -t, --Top					Using top command to get CPU utilization
      -c, --count <num>         set the thread count to show, default is 5.
    Miscellaneous:
      -h, --help                display this help and exit.
    EOF
    }
    
    #1.Collect script parameters
    #2.Check whether PID exists
    if [ $# -gt 0 ];
    then
    	while true; do
    		case "$1" in
    		-c|--count)
    			count="$2"
    			shift 2
    			;;
    		-p|--pid)
    			pid="$2"
    			shift 2
    			;;
    		-t|--top)
    			mode=1
    			shift 1
    			;;
    		-h|--help)
    			usage
    			exit 0;
    			;;
    		--)
    			shift 1;
    			break
    			;;
    		*)
    			shift 1;
    			if [ -z "$1" ] ; then
    				break
    			fi
    			;;
    		esac
    	done
    fi
    if  [ ! -n "$pid" ] ;then
    	echo "error: -p is empty"
    	exit 1;
    fi
    
    if [ `jps |grep $pid |wc -l` -ne 1 ];then 
    	echo "error: -p is wrong"
    	exit 1;
    fi
    
    function workerByJstack(){
    	local tid_hex=$(printf "%x" $tid);
    	echo "====================== tid:${tid}  tid_hex:${tid_hex}  cpu:${cpu}  time:${time} ======================";
    	jstack $pid | awk 'BEGIN {RS = "
    
    +";ORS = "
    
    "} /'${tid_hex}'/ {print $0}';
    	echo "";
    }
    
    function workerByTop(){
    	top -Hp $pid -n1 | sed '1,7d'| sed '$d' |sed '$d' | sort -k 10 -n -r | sed $[$count+1]',$d' | awk '{print $10,$2,$12}' | while read cpu tid time
    	do
    		workerByJstack $pid $tid $cpu $time
    	done
    }
    
    function workerByPs(){
    	#1.Query all threads according to PID.
    	#2.Delete header and first line information.
    	#3.According to the second column of CPU to sort, reverse display.
    	#4.Delete the count + 1 to last column based on the count value.
    	#5.Get CPU utilization, TID value, thread used time, and assign them to CPU, TID, time respectively.
    	#6.Perform hex conversion on TID.
    	#7.Use JDK to monitor all threads of jstack output PID.
    	#8.Use awk to regularly query the thread information of tid_hex required.
    	#9.Display the stack information of count before thread busy.
    	ps -mp $pid -o THREAD,tid,time | sed '1,2d' | sort  -k 2 -n -r |sed $[$count+1]',$d' | awk '{print $2,$8,$9}' | while read cpu tid time
    	do
    		workerByJstack $pid $tid $cpu $time
    	done
    }
    
    function worker(){
    	echo "start-mode:$mode"
    	if [ $mode -eq 0 ];then
    		workerByPs
    	elif [ $mode -eq 1 ];then
    		workerByTop
    	fi
    }
    worker
    
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  • 原文地址:https://www.cnblogs.com/cjunn/p/12185276.html
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