Subj : Re: hyperthreading in database-benchmarks
To   : comp.arch,comp.programming.threads
From : Chris Thomasson
Date : Mon Oct 10 2005 09:45 pm

> 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.

It depends on application design. Two threads on the same core are tightly 
coupled together. You would need to try to ensure that reader threads that 
are bound to a single SMT core access similar data, and preferably execute 
down similar code-paths. Cache locality is very important, false-sharing, 
cache-blocking, ect...

SMT can reduce performance if an application is not properly designed. 
Usually, lock-free designs that avoid atomic operations and StoreLoad style 
memory barriers are able to make "some" performance gains on an SMT 
system...

.