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01-07-2013 07:25 AM
01-07-2013 07:25 AM
ipcs shared memory
Hi
OS version -v1
we are facing issue in DB for nearly 30 days.
instead of adding new physical memory , I have some doubts to be clarified.
is it possible to remove the shared memory .
I have pasted the ipcs output,
$ ipcs -m
IPC status from /dev/kmem as of Fri Jan 4 19:52:34 2013
T ID KEY MODE OWNER GROUP
Shared Memory:
m 0 0x411818ab --rw-rw-rw- root root
m 1 0x4e0c0002 --rw-rw-rw- root root
m 2 0x411c0ba4 --rw-rw-rw- root root
m 1027 0x06347849 --rw-rw-rw- root root
m 9220 0x0c6629c9 --rw-r----- root root
m 1029 0x491003a9 --rw-r--r-- root root
m 82950 0x1550f7c4 --rw-r----- oracle oinstall
m 7 0x5e140004 --rw------- root root
m 1032 0x64541651 --rw-r--r-- oni01 onidev
$ ipcs -mob
IPC status from /dev/kmem as of Fri Jan 4 19:52:55 2013
T ID KEY MODE OWNER GROUP NATTCH SEGSZ
Shared Memory:
m 0 0x411818ab --rw-rw-rw- root root 0 348
m 1 0x4e0c0002 --rw-rw-rw- root root 1 61760
m 2 0x411c0ba4 --rw-rw-rw- root root 1 8192
m 1027 0x06347849 --rw-rw-rw- root root 2 65544
m 9220 0x0c6629c9 --rw-r----- root root 2 18994744
m 1029 0x491003a9 --rw-r--r-- root root 0 22908
m 82950 0x1550f7c4 --rw-r----- oracle oinstall 15 1593843712
m 7 0x5e140004 --rw------- root root 1 512
m 1032 0x64541651 --rw-r--r-- oni01 onidev 0 4
$ ipcs -ma
IPC status from /dev/kmem as of Fri Jan 4 19:53:29 2013
T ID KEY MODE OWNER GROUP CREATOR CGROUP NATTCH SEGSZ CPID LPID ATIME DTIME CTIME
Shared Memory:
m 0 0x411818ab --rw-rw-rw- root root root root 0 348 642 642 14:47:21 14:47:21 14:47:15
m 1 0x4e0c0002 --rw-rw-rw- root root root root 1 61760 642 642 14:47:18 14:47:21 14:47:15
m 2 0x411c0ba4 --rw-rw-rw- root root root root 1 8192 642 654 14:47:18 14:47:15 14:47:15
m 1027 0x06347849 --rw-rw-rw- root root root root 2 65544 1711 1782 14:48:10 14:48:08 14:48:03
m 9220 0x0c6629c9 --rw-r----- root root root root 2 18994744 1738 17595 16:07:24 16:11:49 14:48:07
m 1029 0x491003a9 --rw-r--r-- root root root root 0 22908 1716 1782 19:53:01 19:53:01 14:48:09
m 82950 0x1550f7c4 --rw-r----- oracle oinstall oracle oinstall 15 1593843712 12253 17544 19:52:20 19:52:21 17:04:57
m 7 0x5e140004 --rw------- root root root root 1 512 2063 2063 14:48:32 no-entry 14:48:32
m 1032 0x64541651 --rw-r--r-- oni01 onidev oni01 onidev 0 4 23141 12432 12:30:47 12:30:47 16:42:04
$
$
glance output
Total VM : 3.5gb Sys Mem : 1.2gb User Mem: 2.4gb Phys Mem: 6.0gb
Active VM: 2.7gb Buf Cache: 1.5gb Free Mem: 920mb
total physical memory is 6 GB.
user memory is 2.4 gb.
is it possible to clear the shared memory from the above outputs.
regards
Madhu
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01-07-2013 08:18 AM
01-07-2013 08:18 AM
Re: ipcs shared memory
Doesn't ipcrm(1) work?
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01-07-2013 08:22 AM
01-07-2013 08:22 AM
Re: ipcs shared memory
ipcrm may work, but you really have to be careful when deleting share memory segments. If you delete the wrong one it may adversely affect Oracle.
I would advise to only delete shared memory segments after very careful consideration.
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01-07-2013 08:41 AM
01-07-2013 08:41 AM
Re: ipcs shared memory
Hi Patrick,
Thanks for the response.
without deleting shared memory ,how can I fine tune the oracle performance.
regards'
Madhu
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01-07-2013 12:13 PM
01-07-2013 12:13 PM
Re: ipcs shared memory
>is it possible to clear the shared memory from the above outputs?
82950 0x1550f7c4 --rw-r----- oracle oinstall oracle oinstall 15 1593843712
What do you think you'll be able to do if you remove the SGA? You'll have to stop those 15 processes.
>without deleting shared memory, how can I fine tune the oracle performance.
Add lots more RAM?
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01-07-2013 12:52 PM
01-07-2013 12:52 PM
Re: ipcs shared memory
Shared memory is something that a program requests and uses to exchange data between other processes. Oracle performance is significantly enhanced by increasing the size of SGA (which is shared memory). But if you are running out of memory, Oracle performance cannot be improved.
As Patrick mentioned, removing shared memory segments that are still being used will usually crash the processes that depend on these segments. Now if someone has not been properly shutting down processes that use shared memory (as in: kill -9) then shared memory will be a mess of used and unused segments. It would be nice if unused segments could be identified but the problem is that a segment can be created by one process and used by several others. The creator does not have to stay running for the segment to remain available. In fact, all processes that were using the segment could terminate and start again at a later time using the segment ID to reconnect to the sdhared memory area.
That's why it is dangerous to use ipcrm to remove segments without accurate information about the segments. Most programs never provide a way to identify segments that are active.
The only safe way to recover the memory area is to reboot, then make sure no one uses kill -9 against programs that use shared memory.
In general, Oracle (and most other database engines) will run much faster if the number of disk I/Os are reduced and this can be done by tuning the SGA and parameters that use the SGA. An Oracle performance specialist can look over your current setup and make recommendations. Note that trying to play with the OS to make Oracle run faster is like a slow car where you hope that adding air to the tires will make it go faster instead of getting a bigger motor.
Bill Hassell, sysadmin