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

  1. #1
    Join Date
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    How to kill unreleased memory due to 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

    Last edited by adewri; 02-28-2003 at 09:12 AM.
    Amar
    "There is a difference between knowing the path and walking the path."

    Amar's Blog  Get Firefox!

  2. #2
    Join Date
    Nov 2002
    Posts
    80
    ipcs is part of cygwin so I dont know if this will work on NT?? prolly not i guess.

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