Re: Memory Sizing Advice

From: bhonaker <>
Date: Fri, 9 May 2008 07:56:32 -0700 (PDT)
Message-ID: <>

On May 9, 10:06 am, "" <> wrote:
> On May 9, 8:47 am, bhonaker <> 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"

> 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?

> 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." Received on Fri May 09 2008 - 09:56:32 CDT

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