Re: Memory Sizing Advice

Comments embedded.
On May 9, 9:56 am, bhonaker <bhona..._at_gmail.com> wrote:
> On May 9, 10:06 am, "fitzjarr..._at_cox.net" <orat..._at_msn.com> wrote:
>
> > On May 9, 8:47 am, bhonaker <bhona..._at_gmail.com> wrote:
>
> > > > The question I have is, is there any downside to me buying, say, a 32G
> > > > box and setting the SGA size at 20G? Will I actually end up harming my
> > > > performance with an over-large SGA (assuming I have enough physical
> > > > memory to keep the box out of swap)?
>
> > > Since everyone is busy telling you how to tune instead of answering
> > > your question, you might have to infer that the answer is "No, there
> > > is no downside to adding memory."  That's my takeaway from no
> > > negatives pointed out anyway...
>
> > Then you're not reading the entire thread, as I posted that installing
> > all of the physical memory a server can accept, then allocating 80% of
> > that to the database would be wasteful, to say the least.
>
> To me "wasteful" does not translate to "harming performance"
>

In some cases you're correct, in others you may be wrong. Since you can't witness the affected system 'in action' you can't comment either way.

> > Knowing that this is a Windows operating sytem, which requires 2 gig for the
> > operating system alone, may make that 80% allocation 'impossible' thus
> > creating a scenario of constant paging/swapping to/from disk.  Of
> > course even a successful allocation of that much memory to the SGA
> > would create a paging/swapping situation as PGA components may require
> > more free memory than is available.  Which, in turn, sends performance
> > into the proverbial dumpster.
>
> > Even if he's lucky and no paging occurs it's highly likely his memory
> > allocations will be unused as constantly changing data causes the
> > cache to be refreshed from disk, thus killing the 'benefit' of having
> > all of those lovely data blocks in cache.  And bloating the SGA to
> > starve the O/S is ... not the wisest of moves.
>
> Pat suggested "a 32G box and setting the SGA size at 20G."  Are you
> saying that 12G for the OS would be starving it?
>

Certainly not, and if you read it that way you need to look at the context again. That comment was made with reference to the previous paragraph where, on a smaller 'box', the maximum RAM installable may be 8 gig, and 80% of that would leave less than 2 gig for the O/S, which COULD starve it for resources.

> > The negatives of this situation are known by most of those who have
> > posted to this thread.  Siimply because you can't see them in print is
> > no indication they don't exist.
>
> > David Fitzjarrell
>
> I understand that 99% of the posters here are more knowledgable than
> me.  I am not trying to be argumentative, I simply haven't seen any
> negatives listed - perhaps I need to learn to read between the lines
> better?  All I see is people saying it is wasteful and that there are
> better ways to spend time and money, but I haven't seen anyone say
> "The reason you DON'T want a 20G SGA allocated out of 32G is because
> this will happen and this will happen, you would be better off with a
> 10G SGA allocated out of 32G."

As I said before since you, nor anyone else responding to this thread outside of the O/P, can actually witness this configuration in action it would be foolish to make such a claim.

David Fitzjarrell Received on Fri May 09 2008 - 10:11:12 CDT