Oracle Study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@rh7 ~]# ipcs -a------ Shared Memory Segments --------key        shmid      owner      perms      bytes      nattch     status0x00000000 0          root       644        52         20x00000000 32769      root       644        16384      20x00000000 65538      root       644        268        20x00000000 98307      gdm        600        393216     2          dest0x00000000 131076     gdm        600        393216     2          dest0x00000000 163845     gdm        600        393216     2          dest0x00000000 196614     gdm        600        393216     2          dest0x00000000 229383     gdm        600        393216     2          dest0x4b4218ec 557064     oracle     660        4096       0------ Semaphore Arrays --------key        semid      owner      perms      nsems0x00000000 0          root       600        10x00000000 98305      root       600        10x000000a7 327682     root       600        10xbe61d9cc 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 - ProductionPL/SQL Release 11.2.0.1.0 - ProductionCORE    11.2.0.1.0      ProductionTNS for Linux: Version 11.2.0.1.0 - ProductionNLSRTL 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 memNAME                                 TYPE        VALUE------------------------------------ ----------- ------------------------------hi_shared_memory_address             integer     0memory_max_target                    big integer 300Mmemory_target                        big integer 300Mshared_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 memNAME                                 TYPE                   VALUE------------------------------------ ---------------------- ------------------------------hi_shared_memory_address             integer                0memory_max_target                    big integer            300Mmemory_target                        big integer            0shared_memory_address                integer                016:30:51 SYS@ test3 >startup force ;ORACLE instance started.Total System Global Area  313860096 bytesFixed Size                  1336232 bytesVariable Size             205524056 bytesDatabase Buffers          100663296 bytesRedo Buffers                6336512 bytesDatabase mounted.Database opened.

再看共享内存：

[oracle@rh7 ~]$ ipcs -a------ Shared Memory Segments --------key        shmid      owner      perms      bytes      nattch     status0x00000000 0          root       644        52         20x00000000 32769      root       644        16384      20x00000000 65538      root       644        268        20x4b4218ec 622600     oracle     660        4096       0------ Semaphore Arrays --------key        semid      owner      perms      nsems0xbe61d9cc 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 bytesFixed Size                  1336232 bytesVariable Size             205524056 bytesDatabase Buffers          100663296 bytesRedo Buffers                6336512 bytes16:40:52 SYS@ test3 >show parameter memNAME                                 TYPE                   VALUE------------------------------------ ---------------------- ------------------------------hi_shared_memory_address             integer                0memory_max_target                    big integer            0memory_target                        big integer            0shared_memory_address                integer                016:40:59 SYS@ test3 >show parameter sgaNAME                                 TYPE                   VALUE------------------------------------ ---------------------- ------------------------------lock_sga                             boolean                FALSEpre_page_sga                         boolean                FALSEsga_max_size                         big integer            300Msga_target                           big integer            180M

查看系统共享内存:

[oracle@rh7 ~]$ ipcs -a------ Shared Memory Segments --------key        shmid      owner      perms      bytes      nattch     status0x00000000 0          root       644        52         20x00000000 32769      root       644        16384      20x00000000 65538      root       644        268        20x4b4218ec 884744     oracle     660        316669952  16------ Semaphore Arrays --------key        semid      owner      perms      nsems0xbe61d9cc 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！