delete unused shared memory segments from an Oracle instance

Once upon a time, a dba issues some kill -9 to clean up dying database processes. Or the database instance crashes. This will left some shared memory segments. Note 68281.1 describe how to remove them on a server with multiple databases.

First, list the ipc process

$ ipcs
IPC status from /dev/mem as of Mon Nov 14 11:28:58 CET 2011
T ID KEY MODE OWNER GROUP
Message Queues:
q 0 0x4107001c -Rrw-rw---- root printq

Shared Memory:
m 0 0x7800006f --rw-rw-rw- itmuser1 itmusers
m 1 0x78000070 --rw-rw-rw- itmuser1 itmusers
m 5242882 0x41d2ba80 --rw-r----- oracle dba
m 99614723 0xb0d4d164 --rw-rw---- oracle dba
m 12582917 0xb84cbc28 --rw-rw---- oracle dba
m 79691782 0x1058873f --rw------- oracle dba
m 638582792 0x78000382 --rw-rw-rw- root system
m 218103817 0x780003b7 --rw-rw-rw- root system
Semaphores:
s 1 0x6202c477 --ra-r--r-- root system
s 6291461 0x0102c2d8 --ra------- root system
s 6 0xa100004b --ra-ra-ra- root system


Get a list of the running databases

$ ps -ef | grep pmon | grep -v grep
oracle 483334 1 1 Aug 16 - 6:46 ora_pmon_db03
oracle 1253476 1 0 Oct 31 - 2:00 ora_pmon_db01
oracle 2298042 1 0 Sep 05 - 11:07 ora_pmon_db02

Then, for each database, get the ipc information
$ export ORACLE_SID=db01
$ sqlplus / as sysdba
SQL> oradebug setmypid
Statement processed.
SQL> oradebug ipc
Information written to trace file.
SQL> oradebug tracefile_name
/u01/app/oracle/admin/db01/udump/db01_ora_2625574.trc
$ awk '/Shared Memory:/{getline;getline;print}' /u01/app/oracle/admin/db01/udump/db01_ora_2625574.trc
5242882 0x41d2ba80
$ export ORACLE_SID=db02
$ sqlplus / as sysdba
SQL> oradebug setmypid
Statement processed.
SQL> oradebug ipc
Information written to trace file.
SQL> oradebug tracefile_name
/u01/app/oracle/diag/rdbms/db02a/db02/trace/db02_ora_2441408.trc
$ awk '/Shared Memory:/{getline;getline;print}' /u01/app/oracle/diag/rdbms/db02a/db02/trace/db02_ora_2441408.trc
99614723 0xb0d4d164
$ export ORACLE_SID=db03
$ sqlplus / as sysdba
SQL> oradebug setmypid
Statement processed.
SQL> oradebug ipc
Information written to trace file.
SQL> oradebug tracefile_name
/u01/app/oracle/diag/rdbms/db03b/db03/trace/db03_ora_2617416.trc
$ awk '/Shared Memory:/{getline;getline;print}' /u01/app/oracle/diag/rdbms/db03b/db03/trace/db03_ora_2617416.trc
12582917 0xb84cbc28


Compare it with the first list, and if you are absolutely sure to do what you are doing, remove the oracle segments that are not assigned to any database instance with ipcrm. If possible try first to figure out where they come from and do a shutdown abort of the not-correctly-stopped database.

Ok, with ipcrm


$ ipcrm -m 79691782

I removed the segment that apparently does not relate to any running instance

This could help you if you are really forced to remove some shared memory segments and you cannot afford shutting down other databases.