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[Oracle@ ~]$ uname -a Linux simpleit.domain.cn 2.6.18-194.el5 #1 SMP Fri Apr 2 14:58:35 EDT 2010 i686 athlon i386 GNU/Linux [oracle@ ~]$ cat /etc/RedHat-release CentOS release 5.5 (Final) ipcs确定共享内存的使用情况，该命令用于输出系统中处于active状态的消息队列，共享内存段以及信号量的有关消息。
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DESCRIPTION The ipcs utility shall write information about active interprocess communication facili- ties. Without options, information shall be written in short format for message queues, shared memory segments, and semaphore sets that are currently active in the system. Otherwise, the information that is displayed is controlled by the options specified. -b Write information on maximum allowable size. (Maximum number of bytes in messages on queue for message queues, size of segments for shared memory, and number of semaphores in each set for semaphores.) [oracle@ ~]$ ipcs -b ipcs: invalid option -- b usage : ipcs -asmq -tclup ipcs [-s -m -q] -i id ipcs -h for help. [oracle@ ~]$ ipcs ------ Shared Memory Segments -------- key shmid owner perms bytes nattch status 0xe9b42ad8 2228225 oracle 640 88080384 13 0x8cdf18fc 2359299 oracle 640 528482304 26 ------ Semaphore Arrays -------- key semid owner perms nsems 0xbbe791cc 98304 oracle 640 44 0x9d085d3c 491521 oracle 640 154 ------ Message Queues -------- key msqid owner perms used-bytes messages [oracle@ ~]$ ipcs -m ------ Shared Memory Segments -------- key shmid owner perms bytes nattch status 0xe9b42ad8 2228225 oracle 640 88080384 13 0x8cdf18fc 2359299 oracle 640 528482304 26 通常最好让整个SGA处于一个单一的共享内存段，因为跟踪一个以上的段将需要额外的开销，在这些段来回切换也需要时间。可以增加/etc/sysctl.conf文件kernel.shmmax参数值，以增加一个单一的共享内存段的最大尺寸。# Controls the maximum shared segment size, in bytes
kernel.shmmax = 4294967295
使用ipcs可以查看系统的SGA是否由多个不连续的内存块组成，如果数据库失败，在释放内存时就会出现问题。使用ipcrm命令（仅仅用于在数据库失败之后SGA碎片没有被释放的情况）可以从内存中去除SGA碎片。不要在一个正在运行的数据库中运行ipcrm命令。
ipcrm命令