Re: [PERFORM] ok you all win what is best opteron (I dont want a

[William Yu]

I say most apps because it's true. :) I would suggest that pretty much 
every app (other than video/audio streaming) people think are 
bandwidth-limited are actually latency-limited. Take the SpecFoo tests. 
Sure I would have rather seen SAP/TPC/etc that would be more relevant to 
Postgres but there aren't any apples-to-apples comparisons available 
yet. But there's something to consider here. What people in the past 
have believed is that memory bandwidth is the key to Spec numbers -- 
SpecFP isn't a test of floating point performance, it's a test of memory 
bandwidth. Or is it? Numbers for DC Opterons show lower latency/lower 
bandwith beating higher latency/higher bandwidth in what was supposedly 
bandwidth limited. What may actually be happening is extra bandwidth 
isn't actually used directly by the app itself -- instead the CPU uses 
it for prefetching to hide latency.

Scrounging around for more numbers, I've found benchmarks at Anandtech 
that relate better to Postgres. He has a "Order Entry" OLTP app running 
on MS-SQL. 1xDC beats 2x1 -- 2xDC beats 4x1.

order entry reads
2x248 - 235113
1x175 - 257192
4x848 - 360014
2x275 - 392643
order entry writes
2x248 - 235107
1x175 - 257184
4x848 - 360008
2x275 - 392634
order entry stored procedures
2x248 - 2939
1x175 - 3215
4x848 - 4500
2x275 - 4908


Greg Stark wrote:
William Yu <[EMAIL PROTECTED]> writes:
 

It turns out the latency in a 2xDC setup is just so much lower and most apps
like lower latency than higher bandwidth.
   

You haven't tested anything about "most apps". You tested what the SpecFoo
apps prefer. If you're curious about which Postgres prefers you'll have to
test with Postgres.
I'm not sure whether it will change the conclusion but I expect Postgres will
like bandwidth better than random benchmarks do.
 


---------------------------(end of broadcast)---------------------------
TIP 8: explain analyze is your friend