topic Re: ipcs shared memory in Operating System - HP-UX

ipcs shared memory

madhu22 — Mon, 07 Jan 2013 15:25:00 GMT

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

Re: ipcs shared memory

bobjh — Mon, 07 Jan 2013 16:18:14 GMT

Doesn't ipcrm(1) work?

Re: ipcs shared memory

Patrick Wallek — Mon, 07 Jan 2013 16:22:07 GMT

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.

Re: ipcs shared memory

madhu22 — Mon, 07 Jan 2013 16:41:52 GMT

Hi Patrick,

Thanks for the response.

without deleting shared memory ,how can I fine tune the oracle performance.

regards'

Madhu

Re: ipcs shared memory

Dennis Handly — Mon, 07 Jan 2013 20:13:56 GMT

>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?

Re: ipcs shared memory

Bill Hassell — Mon, 07 Jan 2013 20:52:06 GMT

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.