Large shared memory segments?

Large shared memory segments?

Post by Dave Haverka » Fri, 24 Mar 1995 04:00:47

I guess what I am actually confused on is in the Headers for the
sample code with W. Richard Stevens book "Unix Network Programming"
it has the following:

in "mesg.h"

* You may have to change the 4096 to a smaller value, if message queues
* on your system were configured with "msgmax" less than 4096.

#define        MAXMESGDATA     (4096-16)
                          /* we don't want sizeof(Mesg) > 4096 */

#define MESGHDRSIZE     (sizeof(Mesg) - MAXMESGDATA)
                                /* length of mesg_len and mesg_type */
Anyhow, when I do a getpagesize() it returns 4096...  So, How does
the page size the system uses affect shared memory size, and other
IPC methods?

BTW, the headers on osf machines define SHMMAX   (4*1024*1024)
and on SUNOS 4.1.3 it is defined as 1024*1024.

David Haverkamp


1. What is this large share memory segment owned by root?


My machine is running AIX 4.3.3.

I run the command ipcs -mb. and found :
T        ID     KEY        MODE       OWNER    GROUP     SEGSZ
Shared Memory:
m         0 0x0d05d2ee --rw-rw-rw-     root   system      1440
m         1 0x4704124c --rw-r--r-- informix informix        48
m         2 0x5804124c --rw-r--r-- informix informix      4096
m         3 0x4d04124c --rw-r--r-- informix informix      4096
m         4 0x4904124c --rw-r--r-- informix informix      4096
m         5 0x5004124c --rw-r--r-- informix informix      3222
m         6 0x45041253 --rw-rw-rw- informix informix        96
m         7 0x43041253 --rw-rw-rw- informix informix     97708
m         8 0x42041253 --rw-rw-rw- informix informix     36028
m         9 0x41041253 --rw-rw-rw- informix informix     42148
m        10 0x44041253 --rw-rw-rw- informix informix      2844
m    917515 0x081c90c4 --rw-r-----   oracle      dba  52850688
m   2228236 0x081c8245 --rw-r-----   oracle      dba 102694912
m        13 0x580550f1 --rw-rw-rw-     root   system 134217728
m        14 0x69041274 --rw-rw-rw-     prod     taps     25578

The segment with segment id 13 is very large, about 120MB.
m        13 0x580550f1 --rw-rw-rw-     root   system 134217728

What is this segment for? How can I know which program uses it?
How can I control it? say, reduce the size of it?

Many thanks.


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