Re: Cleanup SGA?

Hi Mark,

You posed a very good question. UNIX Operating system provides excellent features for real time sharing systems, concurrency control, and sharing of system resources for multiple users. When you create a database, Oracle locks certain portion of Memory for the usage of its SGA. It is implemented by Shared Memory Identifiers, and Semaphores. There are several commands in UNIX to identifiy these parameters:

1. ipcs -ba -> list the Shared Memory, and Semaphore details

Shared Memory

 T         ID      KEY        MODE        OWNER    GROUP  CREATOR   SEGSZ
m       4608   0x83e57a20 --rw-r-----   oracle      dba   oracle   62693376 ==>
Size of the SGA
m      12803   0x4adb8b60 --rw-r-----   oracle      dba   oracle   30302208
m       3078   0x0c13d244 --rw-r-----   oracle      dba   oracle   40214528

Semaphores:
T         ID      KEY        MODE        OWNER       CTIME
s    1769472   0x05540745 --ra-r-----   oracle        9:40:36
s    2293761   00000000 --ra-r-----   oracle       23:42:17
s    6750211   0x069d7765 --ra-r-----   oracle     15:12:30
s     327684   00000000 --ra-r-----   oracle       14:57:24

If you have multiple Oracle Instances you would have above listing. If you do an abort of the instance Oracle may not be able to release the entries from the Shared Memory Area of the Operating System Kernel.

2) You have to remove these entries by the following command to remove  Shared Memory entries.

ipcrm -m 4608
ipcrm -s 1769472

3) After removing these entries try submitting ipcs -ba command to verify the status.
4) Start the Oracle instance.

Hope this helps

Prasad Vadlamani
Sr. Oracle DBA
Sydney, Australia

/////The Most Harbour City in the World//////////////////

Mark Brayshaw wrote:

> Hi,
> I've been given the task of installing Oracle 8.0.4 on Solaris 2.7 as a
> practice exercise (having done the first eductaion course for DBA).
> I've gotten through the install procedure and I've set the file structures
> on Solaris to be OFA compliant, I've started setting up tablespaces and
> users etc. -all fine so far. Unfortunately, while in SVRMGRL, I did a
> shutdown immediate, instead of a shutdown normal, and now when I try to
> start my database I eventually get an "ORA-27100: shared memory realm
> already exists" message. The error messages docco recommends that I clean up
> the SGA for the failed instance, but I cannot find a definition of what
> constitutes the SGA. Can anyone give me a simple description of what
> directories or files actuallly constitute the SGA?
>
> Regards
> Mark Brayshaw
Received on Tue Oct 26 1999 - 21:44:59 CDT