topic share mem in Operating System - Linux

share mem

K.C. Chan — Tue, 22 Jan 2002 19:06:55 GMT

All,
Could someone explains what share mem is? How does oracle uses it? what affect does it have on my system's free mem, if I have 2Gb of phys. memory and my shmmax is to 3Gb? Thanks.

Re: share mem

Jeffrey S. Sims — Tue, 22 Jan 2002 19:30:22 GMT

As I understand it you can increase shmmax to whatever value you want. It just sets the maximum that can be used for a single contiguous lump of memory. Usually you would set it to your physical memory size minus kernel requirement and a bit reserved
for programs.

Hope this helps.

Re: share mem

IT Response — Fri, 22 Feb 2002 14:48:04 GMT

Hello,

What Jeffrey states is correct, you can set it to just about anything.

Shared memory segments are allocated by the shmget() function call, and typically this function is called directly by applications like Oracle.

ipcs -m will show shared memory usage.

Shared memory under Linux is no different from System V IPC shared memory found
in most other Unix systems. I would recommend reading
"Advanced UNIX Programming" to get to know how to use shared memory.
Alternative, read linux man pages for shmget, shmctl and shmat.