Re: Sorting Improvements for 8.4

On Thu, 20 Dec 2007, Gregory Stark wrote:

> Surely such machines have kickass memory backplanes too though? How could it
> ever be reasonable to have an i/o controller with more bandwidth than your
> memory?

Dann had the right general numbers here--max of 6.4GB/s between processors 
and you might coax an aggregate of double that out of the DDR RAM with 2 
4-way interleaved banks of memory.  Let's call it 12GB/s theoretical max. 
If the theoretical max of the disks is 2GB/s, that's only a 6:1 headroom, 
and with a decent cache rate it's not outrageous to imagine you could 
bottleneck on memory with some things before you run out of disk 
throughput.

Right now I think a lot of the disk bottlenecks are seek-limited more than 
anything, but SSD will knock that one out for apps that are more about 
throughput than maximum storage.  I could already switch to SDD usefully 
today for some of what I do that's in that category, it's just a bit too 
expensive to do yet; soon, though.

Just trying to usefully estimate where the edge of that back of the 
envelope should go to.

--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD