Subj : Re: hyperthreading in database-benchmarks
To   : comp.arch,comp.programming.threads
From : Joe Seigh
Date : Tue Oct 11 2005 09:07 am

Oliver S. wrote:
> Has anyone found information on how much hyperthreading is able to 
> improve the
> performance of database-workloads (OTP as well as DWH)? As far as I 
> know, data-
> base systems have a un-usually high rate of cache misses and though 
> suffer more
> the latency-"problem" of current memory-subsystems. So I guess, 
> databases will
> profit more from hyperthreading than most other appications.
> 
> And to get some synthetic numbers on how hyperthreading is able to 
> partitially
> compensate the latency-problem, it would make sense to run a memory-latency
> (with the usual pointer-chasing method) benchmark with two thrads; has 
> anyone
> found some numbers on this?

I assume you're talking about running queries which would sequentially
scan memory which isn't cache's strong point since it's LRU optimized.
And it doesn't look like the mfgrs are doubling up on cache for these systems,
so no help here.

You could get help running a hardware scount thread or ganging the queries so
they act as hardware scouts for each other getting some synergism out of the
process.  There probably won't be gang scheduling support from any of the
OSes for a while at least due to the instability of hw design at this point.

Where are the cache hits occurring?  On the index traversals or on the table
data itself or on both?


-- 
Joe Seigh

When you get lemons, you make lemonade.
When you get hardware, you make software.

.