Re: performance/scalability and multiple instances

Ron Bergeron <bergeror_at_asitshouldbe.com> wrote in news:Pine.LNX.4.44.0301271500190.7387-100000_at_machine.asitshouldbe.com:

> 3) Other than CPUs, memory, and I/O, are there any other resources
> that multiple instances on one server contend for? (ie: semaphores,
> locks, whatever)

I think you hit the biggies up there ... not sure if you're considering that the applications may have different I/O profiles. Tuning may be a bear when devices are shared since one tune may be shadowed by another instance. These are things I'd worry about when it comes to tuning for scalability.

> They did voice one opinion that might have some merit. They said
> that if all the instances are running on one large machine, and a
> few of those instances are idle at the time (instantiated, but not
> processing any queries), then the remaining databases can take
> advantage of the unused CPU cycles from the idle instances.

The converse to the above is what happens when all the instances are at full throttle? Are we starving some instances? What happens if we have backups/loads/etc all running? Do we have enough cap on the system for this? Some times people forget to size for these aspects.

HTH!

-- 
Pablo Sanchez, High-Performance Database Engineering
http://www.hpdbe.com