JVM optimization
Linux system tool
top
Use top to view process status:
$ top
top - 10:55:37 up 1234 days, 20:33, 1 user, load average: 26.61, 31.80, 35.25
Tasks: 485 total, 2 running, 483 sleeping, 0 stopped, 0 zombie
%Cpu(s): 82.8 us, 9.4 sy, 0.0 ni, 5.6 id, 0.0 wa, 0.0 hi, 2.2 si, 0.0 st
KiB Mem : 26359952+total, 10300115+free, 79046432 used, 81551928 buff/cache
KiB Swap: 0 total, 0 free, 0 used. 17903020+avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
35253 work 20 0 27.3g 10.6g 11532 S 817.5 4.2 795248:54 java
38200 work 20 0 27.2g 10.4g 11480 S 774.6 4.1 782100:51 java
33196 work 20 0 27.2g 10.5g 11496 S 663.0 4.2 767660:17 java
38110 work 20 0 27.2g 10.4g 11496 S 368.3 4.2 717635:28 java
38489 work 20 0 27.2g 10.5g 11516 S 286.1 4.2 797625:38 java
198487 work 20 0 134384 18352 888 R 64.0 0.0 0:03.06 netstat
120786 work 20 0 21.7g 4.8g 7032 S 15.5 1.9 410952:23 java
120732 work 20 0 21.7g 4.8g 6996 S 11.2 1.9 346910:48 java
120726 work 20 0 21.7g 4.8g 6980 S 10.2 1.9 355160:19 java
120838 work 20 0 21.7g 4.9g 7244 S 5.6 1.9 407095:04 java
198488 work 20 0 113540 976 820 S 2.3 0.0 0:00.13 awk
197696 root 20 0 0 0 0 S 0.7 0.0 0:00.34 kworker/15:2
10 root 20 0 0 0 0 S 0.3 0.0 10342:55 rcu_sched
161 root 20 0 0 0 0 S 0.3 0.0 947:20.63 ksoftirqd/30
18515 root 20 0 573816 14272 2968 S 0.3 0.0 250:14.40 tuned
View a specific process:
$ top -p 35353
top - 10:56:53 up 1234 days, 20:34, 1 user, load average: 29.17, 31.89, 35.03
Tasks: 1 total, 0 running, 1 sleeping, 0 stopped, 0 zombie
%Cpu(s): 43.6 us, 6.3 sy, 0.0 ni, 47.5 id, 0.0 wa, 0.0 hi, 2.6 si, 0.0 st
KiB Mem : 26359952+total, 10297040+free, 78976912 used, 81652208 buff/cache
KiB Swap: 0 total, 0 free, 0 used. 17910000+avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
35253 work 20 0 27.3g 10.6g 11532 S 373.4 4.2 795254:23 java
And press H to view threads:
$ top -p 35253
top - 10:58:20 up 1234 days, 20:35, 1 user, load average: 28.47, 31.40, 34.61
Threads: 968 total, 3 running, 965 sleeping, 0 stopped, 0 zombie
%Cpu(s): 57.2 us, 6.7 sy, 0.0 ni, 33.8 id, 0.0 wa, 0.0 hi, 2.3 si, 0.0 st
KiB Mem : 26359952+total, 10287185+free, 79023616 used, 81704048 buff/cache
KiB Swap: 0 total, 0 free, 0 used. 17905331+avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
35309 work 20 0 27.3g 10.6g 11532 S 71.6 4.2 8159:47 G1 Conc#5
35306 work 20 0 27.3g 10.6g 11532 S 69.3 4.2 8159:23 G1 Conc#2
35308 work 20 0 27.3g 10.6g 11532 S 69.3 4.2 8160:05 G1 Conc#4
35307 work 20 0 27.3g 10.6g 11532 S 69.0 4.2 8160:03 G1 Conc#3
35257 work 20 0 27.3g 10.6g 11532 S 68.3 4.2 8160:12 G1 Conc#0
35305 work 20 0 27.3g 10.6g 11532 S 68.3 4.2 8159:48 G1 Conc#1
35375 work 20 0 27.3g 10.6g 11532 S 13.9 4.2 589:09.39 http-nio-0.0.0.
35469 work 20 0 27.3g 10.6g 11532 S 7.9 4.2 29171:28 http-nio-8442-P
35470 work 20 0 27.3g 10.6g 11532 S 6.3 4.2 27653:44 http-nio-8442-A
189160 work 20 0 27.3g 10.6g 11532 R 6.3 4.2 587:47.64 http-nio-0.0.0.
35457 work 20 0 27.3g 10.6g 11532 S 5.0 4.2 17071:54 http-nio-0.0.0.
35458 work 20 0 27.3g 10.6g 11532 S 4.0 4.2 14972:14 http-nio-0.0.0.
11726 work 20 0 27.3g 10.6g 11532 S 2.0 4.2 487:53.72 http-nio-0.0.0.
35348 work 20 0 27.3g 10.6g 11532 S 1.7 4.2 12352:21 pulsar-timer-5-
35288 work 20 0 27.3g 10.6g 11532 S 1.3 4.2 805:44.45 GC Thread#6
35304 work 20 0 27.3g 10.6g 11532 S 1.3 4.2 804:14.37 GC Thread#22
35284 work 20 0 27.3g 10.6g 11532 S 1.0 4.2 806:37.70 GC Thread#2
35285 work 20 0 27.3g 10.6g 11532 S 1.0 4.2 806:05.20 GC Thread#3
35286 work 20 0 27.3g 10.6g 11532 S 1.0 4.2 805:39.92 GC Thread#4
35287 work 20 0 27.3g 10.6g 11532 S 1.0 4.2 804:21.61 GC Thread#5
35290 work 20 0 27.3g 10.6g 11532 S 1.0 4.2 806:57.15 GC Thread#8
35293 work 20 0 27.3g 10.6g 11532 S 1.0 4.2 807:10.16 GC Thread#11
35294 work 20 0 27.3g 10.6g 11532 S 1.0 4.2 804:48.06 GC Thread#12
35297 work 20 0 27.3g 10.6g 11532 S 1.0 4.2 806:14.76 GC Thread#15
35299 work 20 0 27.3g 10.6g 11532 S 1.0 4.2 806:53.58 GC Thread#17
View threads
查看Java进程
jps
top #shift +m按内存排序
有介绍说可以通过PS命令查看进程的线程占用情况，但这里没能提供更多的信息
ps -mp 31560 -o THREAD,tid,time,rss,size,%mem
jmap命令
jmap [option] <pid>
<none> to print same info as Solaris pmap
-heap to print java heap summary
-histo[:live] to print histogram of java object heap; if the "live"
suboption is specified, only count live objects
-permstat to print permanent generation statistics
...
其中，jmap -histo:live [pid] 可以查看当前Java进程创建的活跃对象数目和占用内存大小。
jmap -dump:live,format=b,file=xxx.xxx [pid] 则可以将当前Java进程的内存占用情况导出来，方便用专门的内存分析工具（例如：MAT）来分析。
jmap -histo:live 31560 | head -n 10
其中：
- [C is a char[]
- [S is a short[]
- [I is a int[]
- [B is a byte[]
- [[I is a int[][]
- 参考文章 [[1]]