Re: Shared memory

"J.D. Fagan" <jdfagan_at_fcicom.com> writes:

>
> Here's content of my /etc/system file for Solaris 2.6:
>
> set shmsys: shminfo_shmmax = 209,715,200
> set shmsys: shminfo_shmseg = 300
> set semsys: seminfo_semmns = 4000
> set semsys: seminfo_semmni = 210
> set rlim_fd_max = 1024
> set rlim_fd_cur = 1024
>
> Does this mean my shared memory space is equal to 206 mb * 300 = 62.914 gb?
>
> And if I only have 0.5 gb of physical RAM, would this be a bad thing for the
> OS? The reason I ask is that Oracle 7.3.2.2 installer apparently modified
> these values to these settings. But they are way over their recommended
> documented values.
>

A process can get multiple areas of shared memory; each time it requests more shared memory a new shared memory *segment* is attached to its address space. Every shared memory segment in the system at any one time has a unique identifier.

With that in mind:

shmsys:shminfo_shmmax

	The maximum size a single shared memory segment can be.
	An application can request less than this (the request
	won't be rounded up to this value) but cannot request
	more in a single segment.  An application could get
	two independent segments both within this limit but
	together over this limit.

shmsys:shminfo_shmmin

	The minimum size of a single shared memory segment.  Usually
	best left at the default of 1 byte (when reflected in your
	address space I guess this will be rounded up to one page).

shmsys:shminfo_shmseg

	The maximum number of shared memory segments that a single
	process can have.  Each must be within the shmmin/shmmax
	limits.

shmsys:shminfo_shmmni

	The maximum number of shared memory identifiers in the
	entire system;  in other words,  the maximum total number
	of uniqie shared memory segments that can exist across
	all processes (two processes sharing the same segment
	obviously don't count)

Gavin Received on Wed Feb 11 1998 - 00:00:00 CST