Removing Shared Memory

Removing Shared Memory

Sometimes after an instance crash you may have to remove Oracle's shared memory segments manually.

To see all shared memory segments that are allocated on the system, execute:

$ ipcs -m

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status
0x8f6e2129 98305      oracle     600        77694523   0
0x2f629238 65536      oracle     640        2736783360 35
0x00000000 32768      oracle     640        2736783360 0           dest

In this example you can see that three shared memory segments have been allocated. The output also shows that shmid 32768 is an abandoned shared memory segment from a past ungraceful Oracle shutdown. Status "dest" means that this memory segment is marked to be destroyed. To find out more about this shared memory segment you can run:

$ ipcs -m -i 32768

Shared memory Segment shmid=32768
uid=500 gid=501 cuid=500 cgid=501
mode=0640 access_perms=0640
bytes=2736783360 lpid=3688 cpid=3652 nattch=0
att_time=Sat Oct 29 13:36:52 2005
det_time=Sat Oct 29 13:36:52 2005
change_time=Sat Oct 29 11:21:06 2005

To remove the shared memory segment, you could copy and paste shmid and execute:

$ ipcrm shm 32768

Another approach to remove shared memory is to use Oracle's sysresv utility. Here are a few self explanatory examples on how to use sysresv:

Checking Oracle's IPC resources:

$ sysresv

IPC Resources for ORACLE_SID "orcl" :
Shared Memory
ID              KEY
No shared memory segments used
Semaphores:
ID              KEY
No semaphore resources used
Oracle Instance not alive for sid "orcl"
$

Instance is up and running:
 

$ sysresv -i

IPC Resources for ORACLE_SID "orcl" :
Shared Memory:
ID              KEY
2818058         0xdc70f4e4
Semaphores:
ID              KEY
688128          0xb11a5934
Oracle Instance alive for sid "orcl"
SYSRESV-005: Warning
Instance maybe alive - aborting remove for sid "orcl"
$

Instance has crashed and resources were not released:

$ sysresv -i

IPC Resources for ORACLE_SID "orcl" :
Shared Memory:
ID              KEY
32768           0xdc70f4e4
Semaphores:
ID              KEY
98304           0xb11a5934
Oracle Instance not alive for sid "orcl"
Remove ipc resources for sid "orcl" (y/n)?y
Done removing ipc resources for sid "orcl"
$