JVM optimization

Linux system tool

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

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：

1. [C is a char[]
2. [S is a short[]
3. [I is a int[]
4. [B is a byte[]
5. [[I is a int[][]

1. 参考文章 [[1]]