Re: What is up with ISM?

David Freitag wrote:
>
< >As far as Oracle is concerned, the main effect of ISM is to lock shared
< >memory segments in RAM, so your SGA won't get paged out. In an ideal
< >world, this won't make a big difference, because you'll have enough RAM to
< >hold all your active processes and your SGA. Even in the real world, your
< >SGA will usually get hit often enough to keep it in RAM, anyway, even
< >though idle processes are getting swapped out. In general, if your SGA
< >does get paged out, either it's too big, or you need more memory.
< >
< >IOW, ISM is nice, and its absence *might* be the cause of your performance
< >problems, but it generally won't make that much difference, so I'd suggest
< >that you look elsewhere.
< >
< >Lastly, ISM is only available on the Sun4m architecture because that's the
< >only system that has the hardware to support it; AFAIK, it will never be
< >available under Sun4u systems.

> 
> My experience confirms the problems that the original author found.
> 
> We just converted from a Sun Enterprise 150 with 256 megs of ram and a
> single processor to a Sun 3000 with 2 cpus and 512 megs of ram with Veritas
> using Oracle 7.3.x and performance dropped dramatically. After thrashing
> about trying to find the source of the problem, the tech support person from
> Oracle said that the
> cause is the lack of intimate shared memory. The ENABLE_ISM parameter
> doesn't work in 2.6 and Sun and Oracle don't have a patch for it as yet.
> 
> It appears that throwing ram at the problem to prevent swapping is the
> solution.

	The previous poster stated that the Sun4u architecture never had
	ISM because the hardware to support it wasn't there. So this rules
	it out for your E150 as well. By the look of it, I'd say it more
	than likely a config issue with the size of shared memory and
	its process usage. If you investigate what had changed in your
	config between the E150 and the E3000, you shoud be able to spot
	the problem. It could be overallocating shared memory or it
	could be that your database application isn't well designed to
	run in an SMP environment.

-am Received on Wed Jun 10 1998 - 00:00:00 CDT