The UNIX and LINUX operating systems allocate memory based on an interprocess communication model (IPC) to manage memory segments for Oracle database environments.
To obtain details on shared memory for UNIX and LINUX, make use of the ipcs command. Details on syntax are illustrated below from within the UNIX and LINUX man pages:
NAME
ipcs : provide information on ipc facilities
SYNOPSIS
ipcs [ -asmq ] [ -tclup ]
ipcs [ -smq ] -i id
ipcs -h
DESCRIPTION
ipcs provides information on the ipc facilities for which the calling process has read access
The -i option allows a specific resource ID to be specified. Only information on this id will be printed.
Resources may be specified as follows:
-m shared memory segments
-q message queues
Determine what Oracle database has a semaphore set
As we have noted, when an Oracle database hangs, you may have leftover background processes, held RAM memory segment and held semaphore sets. When you have multiple instances on a UNIX server and need to release a semaphore set for an Oracle database, you must first determine which semaphore set belongs to your crippled instance.
Unfortunately, you cannot tell with the ipcs sa command which semaphore set belongs to each Oracle database. Here is the Oracle procedure for determining the semaphore set number for an individual Oracle database so that you can remove the semaphores with the ipcs command.
SQL> oradebug setmypid
SQL> oradebug ipc
SQL> !vi /u01/app/oracle/diag/rdbms/orcl/orcl/trace/orcl_ora_13358.trc
*** 2014-09-20 17:35:30.830Processing Oradebug command 'ipc'
Dump of unix-generic skgm context
areaflags 000000f7
realmflags 0000000f
mapsize 00000800
protectsize 00001000
lcmsize 00001000
seglen 00400000
largestsize 000000007ead3000
smallestsize 0000000000400000
stacklimit 0xbda06894
stackdir -1
mode 660
magic acc01ade
Handle: 0x1b0058 `/u01/app/oracle/product/11.2.0/db_1orcl'
Dump of unix-generic realm handle `/u01/app/oracle/product/11.2.0/db_1orcl', flags = 00000000
Area #0 `Fixed Size' containing Subareas 0-0
Total size 00000000001476d4 Minimum Subarea size 00000000
Area Subarea Shmid Stable Addr Actual Addr
0 0 3080200 0x00000020000000 0x00000020000000
Subarea size Segment size
0000000000148000 000000003ec00000
Area #1 `Variable Size' containing Subareas 4-4
Total size 000000003e000000 Minimum Subarea size 00400000
Area Subarea Shmid Stable Addr Actual Addr
1 4 3080200 0x00000020800000 0x00000020800000
Subarea size Segment size
000000003e000000 000000003ec00000
Area #2 `Redo Buffers' containing Subareas 1-1
Total size 000000000047a000 Minimum Subarea size 00000000
Area Subarea Shmid Stable Addr Actual Addr
2 1 3080200 0x00000020148000 0x00000020148000
Subarea size Segment size
000000000047a000 000000003ec00000
Area #3 `Base Allocator Control' containing Subareas 3-3
Total size 0000000000002000 Minimum Subarea size 00000000
Area Subarea Shmid Stable Addr Actual Addr
3 3 3080200 0x000000207fe000 0x000000207fe000
Subarea size Segment size
0000000000002000 000000003ec00000
Area #4 `Slab Allocator Control' containing Subareas 2-2
Total size 000000000023c000 Minimum Subarea size 00000000
Area Subarea Shmid Stable Addr Actual Addr
4 2 3080200 0x000000205c2000 0x000000205c2000
Subarea size Segment size
000000000023c000 000000003ec00000
Area #5 `skgm overhead' containing Subareas 5-5
Total size 000000