Shmmax??

[simply_dba]

Well one of the Know-it-all DBA asked me this question (He was trying to test me )

RAM : 8 G.B
SHMMAX : 2. G.B
SGA (Shared Pool ,Cache...etc) : 4 G.B
Will the instance start ??

I said:
Yes. Two Segments of 2 G.B each will be created.
He Said :
No. You are wrong. The instance won't start.

Am I wrong??

[oracbase]

Hi,

Oracle recommends setting SHMMAX to 4Gb or 0.5 x Physical Memory on the system.

All our systems have SHMMAX set to 4Gb and our SGA are less that 4Gb.

However, I'm not sure if your system will actually create 2 shared memory segments for this case.

Cheers
Oracbase

[hrishy]

Hi SimplyDBA

An application requests a given amount of contiguous shared memory from the OS.
The OS dictates how large of a shared memory segment it will allow with the kernel parameter SHMMAX(Shared Memory Maximum).
If the amount of shared memory requested by the application is greater than SHMMAX, the OS may be granted the shared memory in multiple segments.

Ideally, however, you want the amount requested by the application to be less than SHMMAX so that the application's request can be fulfilled with one shared memory segment.

So bottomline simply dba ur right .

Just found a metalink note 15566.1 (if that gives a boost to your ego and inflates it to infinity :-D)

regards
Hrishy

[simply_dba]

Thanks hrishy !
Too bad i could not see the note .Metalink shows its down (although the date and time is old)

[davey23uk]

nothing wrong with that note

http://metalink.oracle.com/metalink/...T&p_id=15566.1

[simply_dba]

I know. It was my browser's cache problem

[simply_dba]

Ah. The doc as really gave some enlightenment
Just one doubt

With mutliple segements there are two possiblities.The segments can be attached contiguously, so that it appears to one large shared memory segment, or non-contiguously, with gaps between the segments.The formaer wastes less space that could be used for the stack or heap, but depending on alignment requirements for the shared memory (defined by SHMLBA in the kernel), it may not be possible

What is meant by the statement (in italics)?