Re: Migrating From AIX to Windows 2003

On Feb 23, 11:39 am, "Charles Hooper" <hooperc2..._at_yahoo.com> wrote:
> On Feb 23, 12:03 pm, "BD" <robert.d..._at_gmail.com> wrote:
>
>
>
>
>
> > I have a DSS system which has been heavily tuned over the past few
> > years. The system is tuned as well as it likely will be tuned. But
> > it's heavily loaded with jobs.
>
> > We are tasked with Migrating from AIX to Windows 2003.
>
> > I am reviewing the overall architectures, and while both systems will
> > be running 32-bit versions of Oracle, and both have a 32-bit OS
> > kernel, the underlying IBM hardware on the UNIX platform is 64-bit.
>
> > The licensing arrangments at the time were for 32-bit Oracle, hence
> > the 32-bit kernel.
>
> > I'm reviewing the overall platform specs, and am aware of the memory
> > addressing limitations surrounding 32-bit Windows - the /3GB switch, /
> > PAE, etc.
>
> > I am trying to assess from a very high level whether this architecture
> > conversion will impose a significant performance risk. As to disk
> > storage, both systems will access a SAN. I have little details on
> > differences between the SAN configurations, if any.
>
> > SOURCE SYSTEM:
> > AIX 5.2 - platform: IBM,7028-6C4
> > CPUs: 4x64bit @1002MHz
> > RAM: 7168MB
> > Kernel: 32Bit
> > Oracle: 9i 32Bit
>
> > TARGET SYSTEM
> > Windows 2003 Enterprise 32bit
> > CPUs: 4xdual-core 32-..._at_2.6GHz
> > RAM: 16GB
> > Kernel: 32Bit
> > Oracle: 10g 32Bit
>
> > To me, the biggest concern is the hoops needed to be jumped through to
> > access memory under Windows. I'm about to investigate pushing the
> > buffer cache into the PAE range, to free up additional core memory for
> > the PGA and Shared Pool. I'm hoping that will assist with some
> > performance issues we're seeing.
>
> > Any overall comments would be welcome.
>
> > Oh - and the decision to leave AIX has already been made. No going
> > back. ;-)
>
> There was an article written a year or two ago that suggested that on
> a 32 bit version of Windows, Oracle would need roughly 12GB to 16GB of
> memory to offset the performance penality associated with the various
> memory swapping routines that allow a 32 bit operating system to
> address more than 4GB of memory - in other words, the server needs
> 12GB to 16GB of memory for performance equal to that achieved with a
> 2GB or 3GB upper limit of memory per process. I would suggest that
> you look at the 64 bit version of Windows 2003 if you would like to
> use the Windows platform with more than 4GB of memory installed in the
> server.
>
> This might be the article:http://www.dell.com/downloads/global/solutions/oracle_performance_em6...
>
> Charles Hooper
> PC Support Specialist
> K&M Machine-Fabricating, Inc

I think there is a slightly misleading statement on page six of that:

"Queries that access data through full table scans may not benefit as much from large memory buffers and caching. Some tables in DSS systems may grow extremely large. It may not be possible to buffer the entire table in the SGA or to keep it there for extended periods. In these cases, access through disk I/O may actually be preferable to memory access. These queries may be tuned to direct data to the Recycle Buffer cache in the SGA, instead of the Default Buffer Cache. This will cause the table scan data to be flushed out of the SGA quickly, and avoid "flooding" the main cache, which would displace useful data."

Full table scans over 2% of the cache are placed on the tail end of the LRU list, so don't displace warm or hot data in the default cache. Though I'm sure it would be better in other buffers if lots of things are full table scanning, and I've certainly seen putting the most problematic objects in the recycle buffer be magically delicious. And of course, DSS systems may be doing lots of the work in the PGA anyways.

I've probably made the same conceptual mistake at times anyways.

jg

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