Re: [PERFORM] Opteron vs Xeon (Was: What to do with 6 disks?)

[William Yu]

I posted this link a few months ago and there was some surprise over the 
difference in postgresql compared to other DBs. (Not much surprise in 
Opteron stomping on Xeon in pgsql as most people here have had that 
experience -- the surprise was in how much smaller the difference was in 
other DBs.) If it was across the board +100% in MS-SQL, MySQL, etc -- 
you can chalk in up to overall better CPU architecture. Most of the time 
though, the numbers I've seen show +0-30% for [insert DB here] and a 
huge whopping +++++ for pgsql. Why the pronounced preference for 
postgresql, I'm not sure if it was explained fully.

BTW, the Anandtech test compares single CPU systems w/ 1GB of RAM. Go to 
dual/quad and SMP Xeon will suffer even more since it has to share a 
fixed amount of FSB/memory bandwidth amongst all CPUs. Xeons also seem 
to suffer more from context-switch storms. Go > 4GB of RAM and the Xeon 
suffers another hit due to the lack of a 64-bit IOMMU. Devices cannot 
map to addresses > 4GB which means the OS has to do extra work in 
copying data from/to > 4GB anytime you have IO. (Although this penalty 
might exist all the time in 64-bit mode for Xeon if Linux/Windows took 
the expedient and less-buggy route of using a single method versus 
checking whether target addresses are > or < 4GB.)


Jeff Frost wrote:
On Tue, 19 Apr 2005, J. Andrew Rogers wrote:
I don't know about 2.5x faster (perhaps on specific types of loads), 
but the reason Opterons rock for database applications is their 
insanely good memory bandwidth and latency that scales much better 
than the Xeon.  Opterons also have a ccNUMA-esque I/O fabric and two 
dedicated on-die memory channels *per processor* -- no shared bus 
there, closer to real UNIX server iron than a glorified PC.

Thanks J!  That's exactly what I was suspecting it might be.  Actually, 
I found an anandtech benchmark that shows the Opteron coming in at close 
to 2.0x performance:

http://www.anandtech.com/linux/showdoc.aspx?i=2163&p=2
It's an Opteron 150 (2.4ghz) vs. Xeon 3.6ghz from August.  I wonder if 
the differences are more pronounced with the newer Opterons.

-Jeff
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