FAQ
Depending on the platform SGA_MAX_SIZE of shared memory will be
allocated at instance startup. And as you can see Solaris 9 on SPARC is
one of those platforms. As such it makes no sense to have different
values for SGA_TARGET and SGA_MAX_SIZE on those platforms.


HTH -- Mark D Powell --


From: oracle-l-bounce_at_freelists.org
On Behalf Of Tony Jambu
Sent: Friday, June 24, 2005 7:06 AM
To: Oracle-L_at_freelists.org
Subject: 10g DISM on Solaris

Hi

Am trying to setup Oracle's Automatic Shared Memory Mgmt (ASMM) on
Solaris 9 (and 10) and having some issues. Not sure if it is
(i) bug with Oracle
(ii) bug with Solaris 9,
(iii) I screwed up or
(iv) my understanding/assumption is wrong

O/S: Solaris 9(SPARC)
Oracle: 10.1.0.4 (64bit)

spfile has:

SGA_MAX_SIZE=500M
SGA_TARGET=200M

I thought that with the above, oracle will startup with 200M SGA and
_only_ 200M of System memory is allocated. You then have the ability to
dynamically increase it (using ALTER SYSTEM SET sga_target=xxx ) up to
SGA_MAX_SIZE.

Q. Is the above assumption correct?

Some stats and information

# -------------------------------------

# Get Memory Information from Oracle

# -------------------------------------

% sysresv OEM10G

IPC Resources for ORACLE_SID "OEM10G" :
Shared Memory:

ID KEY
7040 0x629dc97c

^^^^

Semaphores:

ID KEY
4718614 0xdf751d7c

Oracle Instance alive for sid "OEM10G"

# -------------------------------------

# Get Memory allocated to Oracle

# -------------------------------------
% ipcs -a | grep 7040
m 7040 0x629dc97c --rw-r----- oracle dba oracle
dba 18 524296192 19547 23979 15:22:46 15:22:46 14:59:24
^^^^
^^^^^^^^^

Notice that it has allocated 500M of memory. I was expecting it to be
200M

% ps -ef | grep dism

root 23069 1 0 14:59:25 ? 0:00 ora_dism_OEM10G

THis shows Oracle's DISM is running.

Q1. When you set SGA_MAX_SIZE=500M and SGA_TARGET_SIZE=200M,

on startup does Solaris allocate 200M or 500M?

# ==========================

# More information

# ==========================

SQL> show sga

Total System Global Area 524288000 bytes

Fixed Size 1303456 bytes
Variable Size 388242528 bytes
Database Buffers 134217728 bytes
Redo Buffers 524288 bytes

SQL> show parameter sga

NAME TYPE VALUE
------------------------------------ -----------
------------------------------
lock_sga boolean FALSE
pre_page_sga boolean FALSE
sga_max_size big integer 500M
sga_target big integer 200M

Q2. Does setting SGA_MAX_SIZE make the Shared Memory non-pagable?
see reply from Howard Rogers & Nuno
http://www.webservertalk.com/archive149-2004-8-333787.html
Also Oracle's manual -

http://download-west.oracle.com/docs/html/B10812_01/appendix_e.htm#sthre
f830

Intimate Shared Memory

On Solaris systems, Oracle Database uses Intimate Shared
Memory (ISM)

for shared memory segments because it shares virtual
memory resources

between Oracle processes. ISM causes the physical memory
for the entire

shared memory segment to be locked automatically.


On Solaris 8 and Solaris 9 systems, dynamic/pageable ISM
(DISM) is

available. This enables Oracle Database to share virtual
memory

resources between processes sharing the segment, and at
the same time,

enables memory paging. The operating system does not
have to lock down

physical memory for the entire shared memory segment.



Q3. How does one proof or disproof that Solaris has Dynamic memory
allocation enabled?


PS: System has been patch and read the following refernece
Enabling Dynamic SGA on Solaris platform - Doc ID: 151222.1
SUN bug. 4675878

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