shared memory

[Lalo_Weng]

Hi, All masters,

Here I have one machine of T600 with Hp-ux 10.20, I need to increase its memory from current 1GB to 4GB with 3 1GB memory module. I understand that I need to increase SWAP space. But someone else tell me that I also need to change the value of tunable kernal parameter: shmmax. I know this parameter is for shared memory, but what is shared memeory and why I need to enlarge this value when I add more memory module? By the way, this machine is a sybase database server.

Thanks in advance.

[Stefan Saliba · Accepted solution]

Shared memory is reserved memory space for storing data structures and data being shared between or among cooperating processes. This eliminates the need for copying or moving data to a seprate location before it can be used by other processes, reducing processor time and overhead as well as memory consumption

shmmax defines the system-wide maximum allowable shared memory segment size in bytes.
The default value is 64megs and the max value is 1024megs on 32 bit systems and 1Tbyte on 64bit system.

given you are using it for a databse application it means that you can have pretty large datastrcutures. well given you will increase the ram size it would be a good idea to boost the parameter up to accomodate larger datastructures.

remember the value cannot exceed the max swap space.

good luck

[Sanjay_6]

Hi,

Here is a thread, if you want to know about shmmax.

http://docs.hp.com//hpux/onlinedocs/os/11i/kcparams/KCparam.ShMmax.html

http://us-support3.external.hp.com/cki/bin/doc.pl/sid=022f6f8604ae73171f/screen=ckiDisplayDocument?docId=200000018911225

Hope this helps.

Regds