How to kill un-released memory after a shutdown abort.

Identifying Which Instance Owns Which Shared memory and Semaphore Segments

Sometimes it happens that after a crash or after an abnormal shutdown the oracle database instance does not release the shared memory or semaphores.

And if you do not know how to find out the unreleased shared memory or semaphores, this how you do it.

How to find which instance owns which shared memory and semaphores

On a Unix machine give the following commands

table1

Code:

$ ipcs -b IPC status from /dev/mem as of Mon Dec 23 11:47:25 IST 2002 T ID KEY MODE OWNER GROUP QBYTES Message Queues: q 0 0x4107001c --rw-rw---- root printq 4194304 T ID KEY MODE OWNER GROUP SEGSZ Shared Memory: m 11 0x00001515 --rw-rw-rw- root system 16 m 12 0x435dce60 --rw-rw-rw- root system 8024 m 13 0x0d01c353 --rw-rw-rw- root system 1440 m 179306510 0xffffffff D-rw------- ias9 dba 1052672 m 20709394 0xec8bc6b4 --rw-r----- ora8i732 dba 328286208 m 39452692 0x62a7d5a4 --rw-r----- oracle9i dba 520896512 m 64487446 0x076d8fb0 --rw-r----- oracle9i dba 437010432 m 56492055 0x02fa8d7c --rw-r----- ora8i732 dba 293888000 m 28442648 0xbe0bab6c --rw-r----- oracle9i dba 520896512 m 4325402 0xc4d72a50 --rw-r----- oracle9i dba 470073344 m 262171 0xffffffff D-rw-r----- oracle9i dba 470073344 m 19005482 0x493f947c --rw-r----- oracle9i dba 486850560 T ID KEY MODE OWNER GROUP NSEMS Semaphores: s 393216 00000000 --ra-ra-ra- imnadm imnadm 4 s 1 0x6201c1b8 --ra-r--r-- root system 1 s 11 0x580038a1 --ra-ra-ra- root system 1

The above table shows the output of the ipcs –b command. This displays the shared memory and the semaphores.

Now how to know which one to kill?

Say the instance ORCL has not released the memory or semaphores.

Do the following

Code:

$ export ORACLE_SID=ORCL $ svrmgrl Oracle Server Manager Release 3.1.7.0.0 - Production Copyright (c) 1997, 1999, Oracle Corporation. All Rights Reserved. Oracle8i Release 8.1.7.0.0 - Production JServer Release 8.1.7.0.0 - Production SVRMGR> connect internal Connected. SVRMGR> oradebug ipc Information written to trace file. SVRMGR> exit Server Manager complete. $

In case you get the error

Code:

SVRMGR> oradebug ipc ORA-00074: no process has been specified SVRMGR>

Then find pid of a background process.

Code:

$ ps –ef|grep smon [or pmon] oracle9i 278798 1 0 11:57:26 - 0:00 ora_smon_FFSYSHCM ora8i732 288438 1 0 Dec 21 - 0:02 ora_smon_CSSREP1 oracle9i 315834 1 0 11:49:58 - 0:00 ora_smon_FF4HCM oracle8i 367370 1 0 11:47:41 - 0:00 ora_smon_PGUATOMR ora8i732 25398 1 0 Dec 21 - 0:32 ora_smon_ORCL

This will give the pid of the instance ORCL which is 25398

Code:

SVRMGR> oradebug setospid 25398 SVRMGR> oradebug ipc Information written to trace file. SVRMGR> exit Server Manager complete. $

This will write down a trace file in your $ORACLE_BASE/admin/ORCL/udump

Extract from the trace file.

Table2

Code:

"ora_48170_orcl.trc" 78 lines, 3673 characters /ora8i732/app/product/admin/ORCL/udump/ora_48170_orcl.trc Oracle8i Release 8.1.7.0.0 - Production JServer Release 8.1.7.0.0 - Production ORACLE_HOME = /ora8i732/app/product/8.1.7 System name: AIX Node name: tcs6m1 Release: 3 Version: 4 Machine: 000F2F7F4C00 Instance name: ORCL Redo thread mounted by this instance: 1 Oracle process number: 8 Unix process pid: 48170, image: oracle@tcs6m1 (TNS V1-V3) *** 2002-12-23 11:46:31.286 *** SESSION ID:(7.1) 2002-12-23 11:46:31.207 Dump of unix-generic skgm context areaflags 00000037 realmflags 0000000f mapsize 00001000 protectsize 00001000 lcmsize 00001000 seglen 00001000 largestsize 00000000c0000000 smallestsize 0000000000400000 stacklimit 0 stackdir -1 mode 640 magic acc01ade Handle: 2011d3d8 `/ora8i732/app/product/8.1.7ORCL' Dump of unix-generic realm handle `/ora8i732/app/product/8.1.7ORCL', flags = 00000000 Area #0 `Fixed Size' containing Subareas 0-0 Total size 0000000000011f94 Minimum Subarea size 00000000 Area Subarea Shmid Stable Addr Actual Addr 0 0 56492055 0000000030000000 0000000030000000 Subarea size Segment size 0000000000012000 0000000011846000 Area #1 `Variable Size' containing Subareas 2-2 Total size 0000000006a99000 Minimum Subarea size 00100000 Area Subarea Shmid Stable Addr Actual Addr 1 2 56492055 000000003ad10000 000000003ad10000 Subarea size Segment size 0000000006b00000 0000000011846000 Area #2 `Database Buffers' containing Subareas 1-1 Total size 000000000acfe000 Minimum Subarea size 00002000 Area Subarea Shmid Stable Addr Actual Addr 2 1 56492055 0000000030012000 0000000030012000 Subarea size Segment size 000000000acfe000 0000000011846000 Area #3 `Redo Buffers' containing Subareas 3-3 Total size 000000000002a000 Minimum Subarea size 00000000 Area Subarea Shmid Stable Addr Actual Addr 3 3 56492055 0000000041810000 0000000041810000 Subarea size Segment size 000000000002a000 0000000011846000 Area #4 `Lock Manager' containing Subareas 5-5 Total size 0000000000002000 Minimum Subarea size 00000000 Area Subarea Shmid Stable Addr Actual Addr 4 5 56492055 0000000041842000 0000000041842000 Subarea size Segment size 0000000000002000 0000000011846000 Area #5 `Java' containing Subareas 4-4 Total size 0000000000008000 Minimum Subarea size 00000000 Area Subarea Shmid Stable Addr Actual Addr 5 4 56492055 000000004183a000 000000004183a000 Subarea size Segment size 0000000000008000 0000000011846000 Area #6 `skgm overhead' containing Subareas 6-6 Total size 0000000000002000 Minimum Subarea size 00000000 Area Subarea Shmid Stable Addr Actual Addr 6 6 56492055 0000000041844000 0000000041844000 Subarea size Segment size 0000000000002000 0000000011846000 Dump of AIX-specific shared memory info Number of internal AIX shared memory segments 1 Segment Shmid Size Attach Addr 1 56492055 293888000 30000000 Maximum processes: = 315 Semaphore identifiers: 393216

From table 1 and table 2 you can see that 56492055 is the shared memory that is no longer required.

Use the ipcrm –m to remove the shared memory segment.

Code:

$ ipcrm –m 56492055

Similarly you can remove the semaphores

Code:

$ ipcrm –s 393216.

Or

To find the Shared Memory id and Semaphore id you can use:

Code:

$ORACLE_HOME/bin/sysresv IPC Resources for ORACLE_SID "ORCL" : Shared Memory: ID KEY 56492055 0x8a85a74c Semaphores: ID KEY 393216 0x4bd4814c Oracle Instance alive for sid "ORCL"

This will save lot of your valuable time when an instance crashes and the shared memory and semaphore is not released, preventing you from starting up the database again.

HTH
Regards

PS:
or simply do

Code:

ipcrm -m `ipcs -map|awk '$9==0 {print $2}'`

$9 gives NATTACH (The no of processes attached to shared memory segment).
For the killed instance this value is 0

$2 gives the shared memory key

:D