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) r-xp (68:03 32811) /lib/libnss_files-2.3.2.so b6ecd000 (4 KB) rw-p (68:03 32811) /lib/libnss_files-2.3.2.so b6ece000 (512 KB) rw-p (68:03 40360) /dev/zero b6f4e000 (1140 KB) rw-p (00:00 0) b706b000 (1224 KB) r-xp (68:03 114692) /lib/tls/libc-2.3.2.so b719d000 (12 KB) rw-p (68:03 114692) /lib/tls/libc-2.3.2.so b71a0000 (12 KB) rw-p (00:00 0) b71a3000 (72 KB) r-xp (68:03 32795) /lib/libnsl-2.3.2.so b71b5000 (4 KB) rw-p (68:03 32795) /lib/libnsl-2.3.2.so b71b6000 (8 KB) rw-p (00:00 0) b71b8000 (52 KB) r-xp (68:03 114696) /lib/tls/libpthread-0.60.so b71c5000 (4 KB) rw-p (68:03 114696) /lib/tls/libpthread-0.60.so b71c6000 (8 KB) rw-p (00:00 0) b71c8000 (132 KB) r-xp (68:03 114694) /lib/tls/libm-2.3.2.so b71e9000 (4 KB) rw-p (68:03 114694) /lib/tls/libm-2.3.2.so b71ea000 (8 KB) r-xp (68:03 32791) /lib/libdl-2.3.2.so b71ec000 (4 KB) rw-p (68:03 32791) /lib/libdl-2.3.2.so b71ed000 (2940 KB) r-xp (68:06 491677) /opt/oracle/product/9.2.0/lib/libjox9.so b74cc000 (1088 KB) rw-p (68:06 491677) /opt/oracle/product/9.2.0/lib/libjox9.so b75dc000 (12 KB) rw-p (00:00 0) b75df000 (4 KB) r-xp (68:06 491685) /opt/oracle/product/9.2.0/lib/libskgxn9.so b75e0000 (8 KB) rw-p (68:06 491685) /opt/oracle/product/9.2.0/lib/libskgxn9.so b75e2000 (4 KB) r-xp (68:06 491567) /opt/oracle/product/9.2.0/lib/libskgxp9.so b75e3000 (4 KB) ---p (68:06 491567) /opt/oracle/product/9.2.0/lib/libskgxp9.so b75e4000 (4 KB) rw-p (68:06 491567) /opt/oracle/product/9.2.0/lib/libskgxp9.so b75e5000 (4 KB) r-xp (68:06 491688) /opt/oracle/product/9.2.0/lib/libodmd9.so b75e6000 (4 KB) rw-p (68:06 491688) /opt/oracle/product/9.2.0/lib/libodmd9.so b75e7000 (4 KB) r-xp (68:03 101245) /etc/libcwait.so b75e8000 (4 KB) rw-p (68:03 101245) /etc/libcwait.so b75ea000 (4 KB) rw-p (00:00 0) b75eb000 (84 KB) r-xp (68:03 32778) /lib/ld-2.3.2.so b7600000 (4 KB) rw-p (68:03 32778) /lib/ld-2.3.2.so bfff8000 (32 KB) rwxp (00:00 0) mapped: 881332 KB writable/private: 12056 KB shared: 827392 KB |
为了避免多个共享内存段，我们可以修改shmmax内核参数，使SGA存在于一个共享内存段中。
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