A long time ago , In a lecture , The command was used ipcs, Find out oracle It's so small , as follows :

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

Today I suddenly thought of , Just in time , To summarize :

Shown above Oracle The shared memory segment is only 4096 Bytes , It's too small , Oh , by the way , I am 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

Oraccle11g Two new parameters are used for memory management :

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

Could it be a parameter memory_max_target I'm making a mistake , Turn it off and try , I set it here as 0, Then restart the database .

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.

Let's look at shared memory :

[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

What's going on? , It hasn't changed ?

Is the parameter not changed correctly , Continue to verify parameters :

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

Sure enough, it didn't change , Is it an order alter system set memory_max_target=0 scope=spfile; It's no use , It can't be set up , But there is no error in setting the command to restart .

Give me a hard command to reset the default value :

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

This is OK , Parameters memory_max_target Finally, it's equal to 0 了 .

Let's see ORACLE Shared memory :

[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

All right ! From 4096 Byte becomes 671088640 Many bytes .
, To sum up, just put the parameters memory_max_target Set to 0 You can see . I don't suggest you change it like this , Just to explain this phenomenon .

The picture above is for children's shoes to think about , No more explanation ...

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