文章目录
Linux 服务器内存处理相关
1、free 命令
2、查看进程的内存占用情况
3、查看内存占用最高的前20
4、动态查看内存的使用情况

Linux 服务器内存处理相关

1、free 命令
以kb形式查看内存使用情况
free


              total        used        free      shared  buff/cache   available
Mem:        7733220     7109448      243856        2340      379916      329752
Swap:             0           0           0

以mb 形式查看内存使用情况
free -m

              total        used        free      shared  buff/cache   available
Mem:           7551        6942         237           2         371         321
Swap:             0           0           0


total:总计物理内存的大小。
used:已使用多大。
free:可用有多少。
Shared:多个进程共享的内存总额。
Buffers/cached:磁盘缓存的大小。


所以空闲内存=free+buffers+cached=total-used

2、查看进程的内存占用情况
pidstat -r -p 14857 1 5  

Linux 3.10.0-957.21.3.el7.x86_64 (iZbp1ey0i1b0ctp4258qn9Z)      12/20/2019      _x86_64_        (4 CPU)

11:58:49 AM   UID       PID  minflt/s  majflt/s     VSZ    RSS   %MEM  Command
11:58:50 AM     0     14857      0.00      0.00 5657180 927892  12.00  java
11:58:51 AM     0     14857      0.00      0.00 5657180 927892  12.00  java
11:58:52 AM     0     14857      0.00      0.00 5657180 927892  12.00  java
11:58:53 AM     0     14857      0.00      0.00 5657180 927892  12.00  java
11:58:54 AM     0     14857      0.00      0.00 5657180 927892  12.00  java
Average:        0     14857      0.00      0.00 5657180 927892  12.00  java

3、查看内存占用最高的前20
ps aux | head -1;ps aux |grep -v PID |sort -rn -k +4 | head -20

4、动态查看内存的使用情况
slabtop

查看某个进程的占用内存情况(以‘device_maintenance’为例)
1.查找进程号
ps -ef | grep 'device_maintenance'  或 ps -aux | grep 'device_maintenance'




2.查看服务器整体内存占用情况1

3.查看服务器整体内存占用情况2
free -h


total: 内存总数
used: 已经使用内存数
free: 完全空闲内存
shared: 多个进程共享的内存
buffers: 用于块设备数据缓冲，记录文件系统metadata（目录，权限，属性等)
cached: 用于文件内容的缓冲
available：真正剩余的可被程序应用的内存数

Centos7手动释放服务器内存：
[root@mail ~]# sync
[root@mail ~]# cat /proc/sys/vm/drop_caches
0
[root@mail ~]# echo 3 > /proc/sys/vm/drop_caches
total 内存总数
used 已经使用的内存
free 空闲的内存
shared 多个进程共享的内存总额
buffers Buffer Cache和cached Page Cache 磁盘缓存的大小
-buffers/cache 的内存：used - buffers - cached
+buffers/cache 的内存：free + buffers + cached

available(可用memory)=free memory+buffers+cached，有些情况cached占用很多资源，算起来数值不对，其实不影响实际使用。

转载于:https://blog.51cto.com/59465168/2337939

某客户有一服务器,shared pool 相关latch出现异常等待,影响系统性能.分析结果:因为系统空闲内存太少,使用太多Paging Space导致该异常;解决办法:1.增加内存，2.在业务接受范围内减小sga等其他和内存消耗相关参数
nmon查看剩余内存
x          Physical  PageSpace |        pages/sec  In     Out | FileSystemCache
x% Used       99.8%     34.9%  | to Paging Space   0.0    0.0 | (numperm) 14.8%
x% Free        0.2%     65.1%  | to File System    0.0   33.0 | Process   63.9%
xMB Used   21452.8MB 11446.1MB | Page Scans        0.0        | System    21.1%
xMB Free (少)-->51.2MB 21321.9MB | Page Cycles       0.0      | Free       0.2%
xTotal(MB) 21504.0MB 32768.0MB | Page Steals       0.0        |           ------
topas查看内存配置
Disk    Busy%     KBPS     TPS KB-Read KB-Writ                   MEMORY
Topas Monitor for host:    p570b03              EVENTS/QUEUES    FILE/TTY
Wed Jan  9 13:30:30 2013   Interval:  2         Cswitch     785  Readch   173.1K
Syscall   54407  Writech  213.1K
CPU  User%  Kern%  Wait%  Idle%                 Reads       118  Rawin         0
ALL   43.6    1.7    0.0   54.8                 Writes      110  Ttyout      352
Forks         0  Igets         0
Network  KBPS   I-Pack  O-Pack   KB-In  KB-Out  Execs         0  Namei         5
Total    84.5    146.0   200.6    26.4    58.1  Runqueue    0.5  Dirblk        0
Waitqueue   0.0
Disk    Busy%     KBPS     TPS KB-Read KB-Writ                   MEMORY
Total     0.0    164.6    17.0     0.0   164.6  PAGING           Real,MB   21504
Faults    12408  % Comp     86 
FileSystem        KBPS     TPS KB-Read KB-Writ  Steals        0  % Noncomp  13 
Total            316.3    17.9  151.5  164.9    PgspIn        0  % Client   13
PgspOut       0
Name            PID  CPU%  PgSp Owner           PageIn        0  PAGING SPACE
oracle      6357252  16.7   8.4 oracle          PageOut      42  Size,MB   32768
oracle     15401474   8.3  70.8 oracle          Sios         42  % Used     35  
oracle     12714542   8.3   8.3 oracle                           % Free     65
oracle      5767556   8.3   8.3 oracle          NFS (calls/sec)
oracle      5898996   8.3 134.9 oracle          SerV2         0  WPAR Activ    0
oracle     17629634   8.3 134.9 oracle          CliV2         0  WPAR Total    0
oracle     13959694   0.0   8.4 oracle          SerV3         0  Press: "h"-help
oracle      5439860   0.0 134.3 oracle          CliV3         0         "q"-quit
内存参数配置
vmo -F -a
--数据库相关参数
minperm% = 3
v_pinshm = 0
lru_file_repage = 0
maxclient% = 90
maxperm% = 90
strict_maxclient = 1
strict_maxperm = 0
page_steal_method = 1
因为是AIX 6.1,这里的vmo配置基本上是oracle 推荐值(大页没有配置,非必须选项)
会话进程占用内存
procmap 15466998
15466998 : oraclewasudb (LOCAL=NO)
100000000            97466K  read/exec         oracle
11000088d             2430K  read/write        oracle
9fffffff0000000         51K  read/exec         /usr/ccs/bin/usla64
9fffffff000cfe2          0K  read/write        /usr/ccs/bin/usla64
900000000b14930          2K  read/exec         /usr/lib/libC.a[shr3_64.o]
9001000a0122930          0K  read/write        /usr/lib/libC.a[shr3_64.o]
900000000af5b00        118K  read/exec         /usr/lib/libC.a[shrcore_64.o]
9001000a0319100         12K  read/write        /usr/lib/libC.a[shrcore_64.o]
900000000ad7000        118K  read/exec         /usr/lib/libC.a[ansicore_64.o]
9001000a030fe00         36K  read/write        /usr/lib/libC.a[ansicore_64.o]
900000000411468          0K  read/exec         /usr/lib/libicudata.a[shr_64.o]
9001000a0121468          0K  read/write        /usr/lib/libicudata.a[shr_64.o]
90000000040f738          2K  read/exec         /usr/lib/libC.a[shr2_64.o]
9001000a0323738          0K  read/write        /usr/lib/libC.a[shr2_64.o]
9000000008ec800       1699K  read/exec         /usr/lib/libC.a[ansi_64.o]
9001000a0324a00        277K  read/write        /usr/lib/libC.a[ansi_64.o]
9000000008c9b00        135K  read/exec         /usr/lib/libC.a[shr_64.o]
9001000a031db00         19K  read/write        /usr/lib/libC.a[shr_64.o]
900000000708180       1732K  read/exec         /usr/lib/libicuuc.a[shr_64.o]
9001000a036bdac        180K  read/write        /usr/lib/libicuuc.a[shr_64.o]
900000000493d80       2510K  read/exec         /usr/lib/libicui18n.a[shr_64.o]
9001000a0399148        270K  read/write        /usr/lib/libicui18n.a[shr_64.o]
900000000473200         91K  read/exec         /usr/lib/libsrc.a[shr_64.o]
9001000a01127a8         55K  read/write        /usr/lib/libsrc.a[shr_64.o]
90000000045a300         98K  read/exec         /usr/lib/libcorcfg.a[shr_64.o]
9001000a04147c8         18K  read/write        /usr/lib/libcorcfg.a[shr_64.o]
900000000b16200        750K  read/exec         /usr/lib/liblvm.a[shr_64.o]
9001000a03dd028        219K  read/write        /usr/lib/liblvm.a[shr_64.o]
900000000444f00         82K  read/exec         /usr/lib/libcfg.a[shr_64.o]
9001000a027b8f0         26K  read/write        /usr/lib/libcfg.a[shr_64.o]
90000000040e3a0          2K  read/exec         /usr/lib/libcrypt.a[shr_64.o]
9001000a0106948          0K  read/write        /usr/lib/libcrypt.a[shr_64.o]
90000000233c860          5K  read/exec         /usr/lib/libc.a[aio_64.o]
9001000a0437568          0K  read/write        /usr/lib/libc.a[aio_64.o]
9000000003efc00        120K  read/exec         /usr/lib/libodm.a[shr_64.o]
9001000a0107cc8         40K  read/write        /usr/lib/libodm.a[shr_64.o]
900000000bd2c80        147K  read/exec         /usr/lib/libperfstat.a[shr_64.o]
9001000a041a960         14K  read/write        /usr/lib/libperfstat.a[shr_64.o]
900000000bf8000          0K  read/exec         /usr/lib/libdl.a[shr_64.o]
9001000a041f000          0K  read/write        /usr/lib/libdl.a[shr_64.o]
9000000024ac100       8680K  read/exec         /oracle/product/10g/lib/libjox10.a[shr.o]
8001000a0000ca0        588K  read/write        /oracle/product/10g/lib/libjox10.a[shr.o]
900000000a96000        257K  read/exec         /usr/lib/libpthreads.a[shr_xpg5_64.o]
9001000a0283000        559K  read/write        /usr/lib/libpthreads.a[shr_xpg5_64.o]
900000000000800       4025K  read/exec         /usr/lib/libc.a[shr_64.o]
9001000a0000020       1047K  read/write        /usr/lib/libc.a[shr_64.o]
Total      123902K
在上表中，标记为read/write的内存即是进程的私有内存，每个会话大概占用内存近6M,数据库大概有80多个会话,占用内存大概,占用内存大概500M左右.
数据库参数配置
SQL> select sum(PGA_ALLOC_MEM)/1024/1024/1024,count(*) from v$process;
SUM(PGA_ALLOC_MEM)/1024/1024/1024   COUNT(*)
--------------------------------- ----------
2.46758329         84
SQL> show parameter pga;
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
_pga_max_size                        big integer 500M
pga_aggregate_target                 big integer 2000M
SQL> show parameter sga
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
lock_sga                             boolean     FALSE
pre_page_sga                         boolean     FALSE
sga_max_size                         big integer 12000M
sga_target                           big integer 10000M
SQL> show sga;
Total System Global Area 1.2583E+10 bytes
Fixed Size                  2117744 bytes
Variable Size            7600082832 bytes
Database Buffers         4966055936 bytes
Redo Buffers               14655488 bytes
当前系统整体ORACLE使用内存汇总：sga 12G+pga 2.5G+process 0.5G,大概占用内存15G,留给系统内存6G左右,系统使用大量交换分区,导致系统性能下降,最明显的为:shared pool相关latch等待异常,具体awr为:
因为系统因为个别session需要大量内存设置_pga_max_size参数,导致部分会话系统占用2.5g内存,建议设置该参数为默认值,并对个别会话独立设置,设置pga_aggregate_target=1.5G,sga_target=sga_max_size=8.5G,awr结果为: