oracle@mydb ~]$ ipcs -a
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x00000000 32768 root 644 72 2
0x00000000 65537 root 644 16384 2
0x00000000 98306 root 644 280 2
0x00000000 1409028 oracle 640 4096 0
0x00000000 1441797 oracle 640 4096 0
0x079918e8 1474566 oracle 640 4096 0
------ Semaphore Arrays --------
key semid owner perms nsems
0x87a36da4 1343489 oracle 640 154
------ Message Queues --------
key msqid owner perms used-bytes messages
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今天突然想起，刚好有空，来总结一下：
上面显示Oracle共享内存段只有4096个字节，这太小了吧，哦，对了，我这是Oracle11g：
sys@OCM> select * from v$version;
BANNER
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
PL/SQL Release 11.2.0.3.0 - Production
CORE 11.2.0.3.0 Production
TNS for Linux: Version 11.2.0.3.0 - Production
NLSRTL Version 11.2.0.3.0 - Production
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Oraccle11g的对内存的管理用了两个新的参数：
sys@OCM> show parameter memory
NAME TYPE VALUE
hi_shared_memory_address integer 0
memory_max_target big integer 1G
memory_target big integer 0
shared_memory_address integer 0
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会不会是参数memory_max_target在作怪呢，把它关了试试，我这里把它设为0，然后重启数据库。
sys@OCM> alter system set memory_max_target=0 scope=spfile;
System altered.
sys@OCM> startup force;
ORACLE instance started.
Total System Global Area 943669248 bytes
Fixed Size 2234000 bytes
Variable Size 541067632 bytes
Database Buffers 394264576 bytes
Redo Buffers 6103040 bytes
Database mounted.
Database opened.
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再看共享内存：
[oracle@mydb ~]$ ipcs -a
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x00000000 32768 root 644 72 2
0x00000000 65537 root 644 16384 2
0x00000000 98306 root 644 280 2
0x00000000 1802244 oracle 640 4096 0
0x00000000 1835013 oracle 640 4096 0
0x079918e8 1867782 oracle 640 4096 0
------ Semaphore Arrays --------
key semid owner perms nsems
0x87a36da4 1736705 oracle 640 154
------ Message Queues --------
key msqid owner perms used-bytes messages
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怎么回事，没变啊？
是不是参数没改对，继续校验参数：
sys@OCM> show parameter mem
NAME TYPE VALUE
hi_shared_memory_address integer 0
memory_max_target big integer 904M
memory_target big integer 0
shared_memory_address integer 0
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果然没改过来，是不是命令alter system set memory_max_target=0 scope=spfile;没用啊，不能怎么设，但这命令本身设置重启也没报错。来个狠一点的命令重置默认值：
sys@OCM> alter system reset memory_max_target;
System altered.
sys@OCM> startup force;
ORACLE instance started.
Total System Global Area 680665088 bytes
Fixed Size 2231352 bytes
Variable Size 276825032 bytes
Database Buffers 394264576 bytes
Redo Buffers 7344128 bytes
Database mounted.
Database opened.
sys@OCM> show parameter mem
NAME TYPE VALUE
hi_shared_memory_address integer 0
memory_max_target big integer 0
memory_target big integer 0
shared_memory_address integer 0
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这下可以了，参数memory_max_target终于等于0了。我们再来看ORACLE共享内存：
[oracle@mydb ~]$ ipcs -a
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x00000000 32768 root 644 72 2
0x00000000 65537 root 644 16384 2
0x00000000 98306 root 644 280 2
0x00000000 1933316 oracle 640 12582912 30
0x00000000 1966085 oracle 640 671088640 30
0x079918e8 1998854 oracle 640 2097152 30
------ Semaphore Arrays --------
key semid owner perms nsems
0x87a36da4 1867777 oracle 640 154
------ Message Queues --------
key msqid owner perms used-bytes messages
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可以了！已从4096字节变成671088640多字节了。
，总结只要把参数memory_max_target设为0就能看到。这里不建议大家去这样改，只是为了解释一下这个现象。上面那幅图留给童鞋们思考，不再解释了。。。
