OracleStudy之案例--通过IPCS查看共享内存之“怪现象”

Oracle Study之案例--通过IPCS查看共享内存之“怪现象” 在Oracle 11gR2环境下，通过ipcs命令查看共享内存，竟然发现分配给Oracle的内存只有4096Bytes，而在Oracle 10g环境下从未发现这种问题！ [root@rh6~]#ipcs-a------SharedMemorySegments--------keyshm

Oracle Study之案例--通过IPCS查看共享内存之“怪现象”

在Oracle 11gR2环境下，通过ipcs命令查看共享内存，竟然发现分配给Oracle的内存只有4096Bytes，而在Oracle 10g环境下从未发现这种问题！

[root@rh6 ~]# ipcs -a
------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status
0x00000000 0          root       644        52         2
0x00000000 32769      root       644        16384      2
0x00000000 65538      root       644        268        2
0x00000000 98307      gdm        600        393216     2          dest
0x00000000 131076     gdm        600        393216     2          dest
0x00000000 163845     gdm        600        393216     2          dest
0x00000000 196614     gdm        600        393216     2          dest
0x00000000 229383     gdm        600        393216     2          dest
0x4b4218ec 557064     oracle     660        4096       0
------ Semaphore Arrays --------
key        semid      owner      perms      nsems
0x00000000 0          root       600        1
0x00000000 98305      root       600        1
0x000000a7 327682     root       600        1
0xbe61d9cc 983043     oracle     660        154
------ Message Queues --------
key        msqid      owner      perms      used-bytes   messages

数据库版本：

16:27:09 SYS@ test3 >select * from v$version;
BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
PL/SQL Release 11.2.0.1.0 - Production
CORE    11.2.0.1.0      Production
TNS for Linux: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production

Oraccle 11g的通过以下两个参数实现内存的自动个管理：

16:27:19 SYS@ test3 >show parameter mem
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
hi_shared_memory_address             integer     0
memory_max_target                    big integer 300M
memory_target                        big integer 300M
shared_memory_address                integer     0

1、会不会是参数memory_max_target有关系呢？把它设为0，然后重启数据库。

16:28:11 SYS@ test3 >alter system set memory_target=0 ;
System altered.

16:36:44 SYS@ test3 >show parameter mem

NAME                                 TYPE                   VALUE
------------------------------------ ---------------------- ------------------------------
hi_shared_memory_address             integer                0
memory_max_target                    big integer            300M
memory_target                        big integer            0
shared_memory_address                integer                0

16:30:51 SYS@ test3 >startup force ;
ORACLE instance started.
Total System Global Area  313860096 bytes
Fixed Size                  1336232 bytes
Variable Size             205524056 bytes
Database Buffers          100663296 bytes
Redo Buffers                6336512 bytes
Database mounted.
Database opened.

再看共享内存：

[oracle@rh6 ~]$ ipcs -a
------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status
0x00000000 0          root       644        52         2
0x00000000 32769      root       644        16384      2
0x00000000 65538      root       644        268        2
0x4b4218ec 622600     oracle     660        4096       0
------ Semaphore Arrays --------
key        semid      owner      perms      nsems
0xbe61d9cc 1114115    oracle     660        154
------ Message Queues --------
key        msqid      owner      perms      used-bytes   messages

发现分配给Oracle的共享内存仍然很小，看来不是memory_target 参数的问题！

2、尝试调整memory_max_target参数，将其恢复到系统默认值：

16:39:49 SYS@ test3 >alter system set sga_max_size=300m scope=spfile;
System altered.

16:40:06 SYS@ test3 >alter system reset memory_max_target scope=spfile sid='*';
System altered.

16:40:40 SYS@ test3 >startup force nomount;
ORACLE instance started.
Total System Global Area  313860096 bytes
Fixed Size                  1336232 bytes
Variable Size             205524056 bytes
Database Buffers          100663296 bytes
Redo Buffers                6336512 bytes

16:40:52 SYS@ test3 >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

16:40:59 SYS@ test3 >show parameter sga
NAME                                 TYPE                   VALUE
------------------------------------ ---------------------- ------------------------------
lock_sga                             boolean                FALSE
pre_page_sga                         boolean                FALSE
sga_max_size                         big integer            300M
sga_target                           big integer            180M

查看系统共享内存:

[oracle@rh6 ~]$ ipcs -a
------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status
0x00000000 0          root       644        52         2
0x00000000 32769      root       644        16384      2
0x00000000 65538      root       644        268        2
0x4b4218ec 884744     oracle     660        316669952  16
------ Semaphore Arrays --------
key        semid      owner      perms      nsems
0xbe61d9cc 1638403    oracle     660        154
------ Message Queues --------
key        msqid      owner      perms      used-bytes   messages

看来是设置了memory_max_target参数的原因，导致通过ipcs查看到分配给Oracle的内存为4096Bytes！