Re: Memory Sizing Advice

From: <>
Date: Fri, 9 May 2008 07:06:26 -0700 (PDT)
Message-ID: <>

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. 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.

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 Received on Fri May 09 2008 - 09:06:26 CDT

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