[Pacemaker] Resource capacity limit

[Michael Schwartzkopff]

Am Donnerstag, 5. November 2009 21:37:23 schrieb Andrew Beekhof:
> On Thu, Nov 5, 2009 at 8:50 PM, Michael Schwartzkopff <misch at multinet.de> 
wrote:
> > Hi,
> >
> > on the list was a discussion about resource capacity limits. Yan Gao also
> > implemented it.
> >
> > As far as I understood the discussion the solution is to attach nodes and
> > resources capacity limits. Resources are distributed on the nodes of a
> > cluster according to its capacatiy needs. They would be migrated or
> > shutdown if the capacity limits on the node are not met.
> >
> > My question is: Can the capacity figures of the resources be made
> > dynamically?
>
> You can, but you probably don't want to.
> For example, free RAM and CPU load are two things that absolutely make
> no sense to include in such calculations.
>
> Consider how it works:
>
> - The node starts and reports 2Gb of RAM
> - We place a service there that reserves 512Mb
> - The cluster knows there is 1.5Gb remaining
> - We place two more services there that also reserve 512Mb each
>
> If the amount of RAM at the beginning was the amount free, then when
> you updated it to be 512Mb the PE would run and stop two of the
> resources!

Stop. I do not want to make the capacity of the nodes dynamically but the 
actual resource consumption of the resources (i.e the database).

It sometimes happens that resource (i.e. RAM) consumption of resources varies 
and I wanted to make that number dynamical. So after some kind of damping the 
node that started swapping out the resources could migrate resources to a node 
with free capacities.

> You always want to feed the cluster the total amount of RAM installed
> which, at most, you'd query when the cluster starts on that node.

The amount of capacity of any resource (RAM, CPU, ...) of a node should be 
fixed. That makes sense because a node does not get more resources if switched 
on.

Greetings,

Michael.