Re: 10G - editing SPFILE

From: Holger Baer <holger.baer_at_science-computing.de>
Date: Thu, 21 Oct 2004 12:00:32 +0200
Message-ID: <cl81c0$amg$1@news.BelWue.DE>

Howard J. Rogers wrote:
> Holger Baer wrote:
>
>
>

>>In addition to what HJR said, lowering your sga_target changes nothing
>>with regard to the memory that gets allocated on instance startup.

>
>
> I don't think that's quite right, Holger. Not entirely, anyway. Here's a
> quick test:
>

[...]
Nice demonstration and thanks for that. I didn't realize you could reset sga_max_size, which effectivly puts it to a value identical to sga_target. What I was meaning though, is what you describe in the next paragraph:
>
> So the "Total System Global Area" matches the 132M of the MAX_SIZE and not
> the 64M of the TARGET.

Exactly. The "Total System Global Area" is more or less the size of the shared memory segment that get's allocated at instance startup according to the value of sga_max_size. You can see that using ipcs. If you reset sga_max_size, the value of sga_max_size is effectively set to sga_target.

>
> I find that confusing myself, since I would have thought TARGET was what you
> would originally get allocated, and MAX_SIZE just sets a ceiling on what
> you can expand to, dynamically, over time.

I'm not a system programmer, but I guess that resizing a shared memory segment is either not possible or nothing you wan't to do in a hurry. And allocating several different sized shared mem segments is understandably also not desireable.

>
> I've still to get my head around all this 10g automation, I guess!
>
> It does mean that your original statement is likely to be practically true
> for the OP. But as well as lowering his SGA_MAX_SIZE, he could abolish it
> altogether to allow the TARGET to kick in.

Ok, once again, I've learned my lesson :-) I was under the impression, that you had to specify sga_max_size and set or leave sga_target at your leisure, not the other way round. At least, that's how I understood it from the 10g New Features Seminar.

Cheers,

Holger Received on Thu Oct 21 2004 - 05:00:32 CDT