Linux上shmmax参数的设置及含义
shmmax内核参数定义单个共享内存段的最大值，如果该参数设置小于Oracle SGA设置，那么SGA就会被分配多个共享内存段。这在繁忙的系统中可能成为性能负担，带来系统问题。Linux上该参数的缺省值通常为32M。
[root@neirong root]# more /proc/sys/kernel/shmmax
33554432
可以通过ipcs命令查看此设置下共享内存的分配，我们可以看到Oracle分配了多个共享内存段以满足SGA设置的需要:
[root@neirong root]# ipcs -sa
------ Shared Memory Segments --------
key
shmid
owner
perms
bytes
nattch
status
0x00000000 884736
oracle
640
4194304
14
0x00000000 917505
oracle
640
33554432
14
0x00000000 950274
oracle
640
33554432
14
0x00000000 983043
oracle
640
33554432
14
0x00000000 1015812
oracle
640
33554432
14
0x00000000 1048581
oracle
640
33554432
14
0x00000000 1081350
oracle
640
33554432
14
0x00000000 1114119
oracle
640
33554432
14
0x00000000 1146888
oracle
640
33554432
14
0x00000000 1179657
oracle
640
33554432
14
0x00000000 1212426
oracle
640
33554432
14
0x00000000 1245195
oracle
640
33554432
14
0x00000000 1277964
oracle
640
33554432
14
0x00000000 1310733
oracle
640
33554432
14
0x00000000 1343502
oracle
640
33554432
14
0x00000000 1376271
oracle
640
33554432
14
0x00000000 1409040
oracle
640
33554432
14
0x00000000 1441809
oracle
640
33554432
14
0x00000000 1474578
oracle
640
33554432
14
0x00000000 1507347
oracle
640
33554432
14
0x00000000 1540116
oracle
640
33554432
14
0x00000000 1572885
oracle
640
33554432
14
0x00000000 1605654
oracle
640
33554432
14
0x00000000 1638423
oracle
640
33554432
14
0x00000000 1671192
oracle
640
33554432
14
0x00000000 1703961
oracle
640
33554432
14
0x7a9c9900 1736730
oracle
640
4194304
56
------ Semaphore Arrays --------
key
semid
owner
perms
nsems
0xfcf02e10 229376
oracle
640
154
------ Message Queues --------
key
msqid
owner
perms
used-bytes
messages
使用pmap我们可以看到每个共享内存段的地址空间
[root@neirong root]# ps -ef|grep 3102
oracle
3102
1
0 09:27 ?
00:00:26 ora_dbw0_hsmkt
root
3447
3397
0 10:39 pts/4
00:00:00 grep 3102
[root@neirong root]# pmap 3102
ora_dbw0_hsmkt[3102]
08048000 (37308 KB)
r-xp (68:06 1525072)
/opt/oracle/product/9.2.0/bin/oracle
0a4b7000 (8804 KB)
rw-p (68:06 1525072)
/opt/oracle/product/9.2.0/bin/oracle
0ad50000 (380 KB)
rw-p (00:00 0)
50000000 (4096 KB)
rw-s (00:04 884736)
/SYSV00000000
51000000 (32768 KB)
rw-s (00:04 917505)
/SYSV00000000
53000000 (32768 KB)
rw-s (00:04 950274)
/SYSV00000000
55000000 (32768 KB)
rw-s (00:04 983043)
/SYSV00000000
57000000 (32768 KB)
rw-s (00:04 1015812)
/SYSV00000000
59000000 (32768 KB)
rw-s (00:04 1048581)
/SYSV00000000
5b000000 (32768 KB)
rw-s (00:04 1081350)
/SYSV00000000
5d000000 (32768 KB)
rw-s (00:04 1114119)
/SYSV00000000
5f000000 (32768 KB)
rw-s (00:04 1146888)
/SYSV00000000
61000000 (32768 KB)
rw-s (00:04 1179657)
/SYSV00000000
63000000 (32768 KB)
rw-s (00:04 1212426)
/SYSV00000000
65000000 (32768 KB)
rw-s (00:04 1245195)
/SYSV00000000
67000000 (32768 KB)
rw-s (00:04 1277964)
/SYSV00000000
69000000 (32768 KB)
rw-s (00:04 1310733)
/SYSV00000000
6b000000 (32768 KB)
rw-s (00:04 1343502)
/SYSV00000000
6d000000 (32768 KB)
rw-s (00:04 1376271)
/SYSV00000000
6f000000 (32768 KB)
rw-s (00:04 1409040)
/SYSV00000000
71000000 (32768 KB)
rw-s (00:04 1441809)
/SYSV00000000
73000000 (32768 KB)
rw-s (00:04 1474578)
/SYSV00000000
75000000 (32768 KB)
rw-s (00:04 1507347)
/SYSV00000000
77000000 (32768 KB)
rw-s (00:04 1540116)
/SYSV00000000
79000000 (32768 KB)
rw-s (00:04 1572885)
/SYSV00000000
7b000000 (32768 KB)
rw-s (00:04 1605654)
/SYSV00000000
7d000000 (32768 KB)
rw-s (00:04 1638423)
/SYSV00000000
7f000000 (32768 KB)
rw-s (00:04 1671192)
/SYSV00000000
81000000 (32768 KB)
rw-s (00:04 1703961)
/SYSV00000000
83000000 (4 KB)
r--s (00:04 1736730)
/SYSV7a9c9900
83001000 (644 KB)
rw-s (00:04 1736730)
/SYSV7a9c9900
830a2000 (4 KB)
r--s (00:04 1736730)
/SYSV7a9c9900
830a3000 (3444 KB)
rw-s (00:04 1736730)
/SYSV7a9c9900
b6ec2000 (44 KB)
