max limitation for shmmax on system with 8g of ram

[K.C. Chan]

not sure if this is the right place to post this question or under the db section under hp. Here's my question:

share memory:
------ Shared Memory Limits --------
max number of segments = 4096
max seg size (kbytes) = 4194303
max total shared memory (kbytes) = 8388608
min seg size (bytes) = 1

I am running advance redhat 3 with default kernel: "2.4.21-27.ELsmp". As far as max share mem seg size is concern, I am guessing this is the limitation for this kernel because the max mem on it is 8g and I take it share seg size is maxed out at half of physical mem. Could some one confirm? Thanks

[Steven E. Protter]

You should be able to designate at least 100% of physical memory to shmmax. It won't actually use that much unless its requested.

Oracle ias 10g requires that setting on many OS's.

SEP

[K.C. Chan]

Steven, I am not sure what I am doing wrong here. When I set shmmax to "4294967295", the seg size is listed as 4Gbytes. However when I set it to "5294967295", the segment size is listed as "0". Any idea?

On another note, withthe segment size of 4G, I am having problem creating an instance when sga size is 3.1Gbytes. The error is ORA-27123. However when I manually set the sga to around 2Gbytes, I am able to create the instance. Any idea?

[Steven E. Protter]

Yeah,

You are running 32 bit Linux. Oracle can't address more than 2 GB of memory without use of the Linux equivalent of hpux memory windows.

I don't think 32 bit oracle can address more than 2 GB of Ram under andy cicrumcstances.

Can you tell me your Linux distribution, processor and Oracle versions please.

SEP

[K.C. Chan]

steven,
Intel(R) Xeon(TM) MP CPU 3.00GHz
10g
RHEL 3 update 4.

[Steven E. Protter]

That verifies my conclusions.

The most amount of memory that Oracle can address without major kernel changes (you are better off with Itanium and hpux) is 2 GB.

Those SGA's are kind of big. We run some pretty large databases here (13 GB) with SGA's around 350 MB.

OF course we're running our databases on HP-UX PA-RISC 64 bit.

SEP

[K.C. Chan]

steven, I too run hpux. But I also have oracle on linux. yeah, I know the size of the sga is big. But I am planning ahead, if I ever needed to increase the sga size, I want to know what is my limit. In this case, 2G Bytes. Thanks.

[xyko_1]

Hi KC,

I suggest that you read http://www.oracle.com/technology/tech/linux/pdf/linuxVM-WP-022703.pdf

I have Oracle 9i running on smp servers with 8 Gb of RAM and with RH AS21 and 4 Gb of shared memory. The sga has to be a little smallest than 4 Gb.

regards,
xyko