Re: Value of SHMLBA?


<christianeriksson@xxxxxxxxxxx> wrote in message
news:1179645575.622845.40260@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On 18 Maj, 11:39, thom...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
so-tickle-me (Thommy M.) wrote:
christianeriks...@xxxxxxxxxxx writes:
On 18 Maj, 09:42, "Thommy M. Malmström" <thommy.m.malmst...@xxxxxxxxx>
wrote:
christianeriks...@xxxxxxxxxxx wrote:
Hi!

How do I find the value of the system parameter SHMLBA?

It's described in Rich Teer's book "Solaris Systems Programming" page
908ff.
I'm to lazy to read in on it...

Also have a look in /usr/include/sys/shm.h

I've looked into the shm.h file and found

$ grep -i SHMLBA /usr/include/sys/shm.h
#define SHMLBA PAGESIZE /* segment low boundary address
multiple */
/* (SHMLBA must be a power of 2)
*/
#define SHMLBA
(_sysconf(_SC_PAGESIZE))
#define SHM_RND 020000 /* round attach address to SHMLBA */

but I still don't know what the value of SHMLBA is. How do I use the
info in shm.h to find out?

Does the SHMLBA differ from the page size?

$ pagesize
8192

I'm actually not that familiar with this details.

grep PAGESIZE /usr/include/sys/*.h
[...]
/usr/include/sys/param.h:#define PAGESIZE
(_sysconf(_SC_PAGESIZE))
[...]

Here's an online doc that might be
helpfulhttp://www.sun.com/blueprints/0304/817-5917.pdf- Dölj citerad
text -

- Visa citerad text -

This thread is part of trying to explain an oracle shared memory
allocation issue. We have an oracle instance that's trying to allocate
more memory than the parameter sga_max_size is set to.

sga_max_size=4294967296

From the oracle alert-log:

............
WARNING: EINVAL creating segment of size 0x0000000101400000
fix shm parameters in /etc/system or equivalent
............

0x0000000101400000 is a decimal value of 4315938816.

# grep shmmax /etc/system
set shmsys:shminfo_shmmax=4294967296

For oracle the value of shmsys_shmmax is recommended to be 2GB-1 that is:
set shmsys:shminfo_shmmax=4294967295

That really does not have a direct bearing on sga_max_size which is an
Oracle parameter.
What happens if you define an sga larger than a single shared memory segment
is that Solaris will setup a couple of
segments to handle the total size (see ipcs -am and for semiphores see
ipcs -as).

Also the use of sga_max_size may not be what you want. It puts a limit on
the sga size, but the idea is to set it
to a value larger than the sga so thay you can dynamically alter
db_cache_siz for example with a command like
alter system set db_cache_size=3G scope=both and have it work without an
instance bounce.


.

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