Java advanced interview questions-server slowdown in production environment, diagnosis ideas and performance evaluation

The server in the production environment slows down, talk about diagnosis ideas and performance evaluation

There are many reasons for server slowdown in the production environment. Look at the whole machine, CPU, memory, disk, network IO, etc., and optimize according to the specific situation.

Whole machine: top command

The top command is a commonly used performance analysis tool under Linux, which can display the resource usage of each process in the system in real time .

We know that to determine the load of a system, you can use top , uptime and other commands to view load averageit . It records the average load of the system for one minute, five minutes, and fifteen minutes.

$ top

The sum of the three values ​​of load average is divided by 3 and then multiplied by 100%. If it is higher than 60%, the system load is large.

cpu：vmstat

The vmstat command reports statistics about kernel threads, virtual memory, disks, traps, and CPU activity. The reports generated by the vmstat command can be used to balance system load activity. The system-wide statistics (in all processors) calculate the average value expressed as a percentage, or calculate the sum.

$ vmstat -n 2 3

additional

View all cpu core information

mpstat -P ALL 5 2

Indicates that a report is generated every 5 seconds, and a total of 2 reports are generated.

Detailed explanation of mpstat command parameters in Linux

Decomposition information of CPU usage by each process

pidstat is mainly used to monitor the occupancy of system resources by all or specified processes, such as CPU, memory, device IO, task switching, threads, etc. When pidstat is run for the first time, it displays various statistics from the start of the system, and running pidstat afterwards will display the statistics since the last time the command was run. Users can obtain the required statistical information by specifying the number and time of statistics.

pidstat use -poptions, we can view the system resource usage of a specific process.
Using -uoptions, pidstat will display the cpu usage statistics of each active process . The effect of pidstat -uexecution is pidstatthe same as that of individual execution .

pidstat -u 1 -p 进程编号

Sampling every second, print out the details.

Memory: free

How to observe the memory usage problem, free is a very useful command. The
parameter -mdisplays the memory usage in MB.

$ free
              total        used        free      shared  buff/cache   available
Mem:        4000436     1192152      266780       53844     2541504     2468412
Swap:       4194300         524     4193776

$ free -g
              total        used        free      shared  buff/cache   available
Mem:              3           1           0           0           2           2
Swap:             3           0           3

$ free -m
              total        used        free      shared  buff/cache   available
Mem:           3906        1163         260          52        2482        2410
Swap:          4095           0        4095

Experience

• Application available memory/system physical memory>70% sufficient memory
• Application available memory / system physical memory <20% insufficient memory, need to increase memory
• 20%<application available memory/system physical memory<70% memory is basically enough

additional

pidstat use -roption, pidstat will display the memory usage statistics of each active process

pidstat -p 进程号 -r 采样间隔秒数

Detailed explanation of the pidstat command for real-time monitoring of Linux running processes

Disk: df

$ df -h
文件系统        容量  已用  可用 已用% 挂载点
udev            1.9G     0  1.9G    0% /dev
tmpfs           391M  1.5M  390M    1% /run
/dev/sda1        28G   20G  7.1G   74% /
tmpfs           2.0G     0  2.0G    0% /dev/shm
tmpfs           5.0M  4.0K  5.0M    1% /run/lock
tmpfs           2.0G     0  2.0G    0% /sys/fs/cgroup
tmpfs           391M   20K  391M    1% /run/user/1000

As you can see, 28G has used 20G, 74% of which have been used

Disk: IO

Iostat is mainly used to monitor the IO load of system equipment. When iostat is run for the first time, it displays various statistical information from the start of the system. After that, running iostat will display the statistical information since the last time the command was run. Users can obtain the required statistical information by specifying the number and time of statistics.

iostat -xdk 2 3

Parameter -dindicates, the display device (disk) used state; -kthe use of certain block in units of column enforce Kilobytes units; represents 2, data refresh every 2 seconds. 3 means, sampling 3 times.

additional

pidstat use -doptions, we can view the statistics of the process IO

pidstat -d 采样间隔秒数 -p 进程号

The program here is an endless loop printing program, so disk IO does not occupy much.

Network IO

The ifstat tool is a network interface monitoring tool, which is relatively simple to look at network traffic

Download
http://gael.roualland.free.fr/ifstat/ (official website)

wget http://gael.roualland.free.fr/ifstat/ifstat-1.1.tar.gz

Compile and install

tar -zxvf ifstat-1.1.tar.gz
cd ifstat-1.1
./configure            #默认会安装到/usr/local/bin/目录中
make
make  install

Note: Execution which ifstatoutput /usr/local/bin/ifstat

#ifstat
       eth0                eth1       
 KB/s in  KB/s out   KB/s in  KB/s out
    0.07      0.20      0.00      0.00
    0.07      0.15      0.58      0.00

reference

16 Linux server monitoring commands you need to know
Linux/Unix notebook