[Pacemaker] placement-strategy=minimal - placing and logging

[Vladimir]

On Fri, 8 Mar 2013 11:05:01 +0100
Lars Marowsky-Bree <lmb at suse.com> wrote:

> On 2013-03-07T21:34:47, Vladimir <ml at foomx.de> wrote:
> 
> > All resources are only able to run if they are distributed in the
> > right combination. A working example could like:
> 
> The algorithm is somewhat simplistic, which has the advantage of being
> fast. It works "quite well" in scenarios where there's a number of
> nodes available and differences between resources are not so large,
> but it won't always find the "optimal" solution.
> 
> Optimal placement (rucksack problem) is NP-complete, so all realistic
> algorithms implement heuristics.
> 
> In theory, the case you describe is probably one that can be solved
> easily enough, but the current one doesn't. We do accept patches ;-)
> 
> (If someone is looking for a master's thesis topic, transforming the
> constraints into linear equations and applying an appropriate
> optimization function for location scores/utilization and finding a
> discrete solution using one of the available libraries is probably the
> way to go.)

I understand the main problem. I just hoped there is another approach.

> > Is there a possibility to configure it in another way?
> 
> You can influence the placement of resources using resource
> priorities, but of course that gets a bit hackish for larger
> configurations and not exactly automatic.
> 
> If you know the work packaes exactly, you can also use collocation
> sets. That's quite feasible for a low node count, which is where the
> current algorithm is least effective.

Collocations were exactly what I try to avoid. The setup is planned to
get >15 resources (and an upper limit is not defined). I think it would
get pretty hard to consider all possible collocations, especially if a
kind of automated deployment is regarded. Using larger sets of
collocation makes the configuration more difficult to read an
especially to maintain.

> > Furthermore if there is a lack of configured cores and thus a
> > resource cannot be started I don't see any log messages or crm_mon
> > output.
> 
> This part is normal, yes. You don't get an error message if -inf
> colocation constraints prevent a resource from being placed, either.

Ok, I see but I'm looking for a possibility to monitor such states to
be informed if a resource can't be started because of lack of provided
utilization. 

Does anybody has an idea about that issue? 

crm_simulate got mentioned by Michael but I'm not sure wether it is the
right tool for a monitoring purpose.

> >    dc-version="1.1.6-9971ebba4494012a93c03b40a2c58ec0eb60f50c" \
> 
> There have been some fixes/improvements to utilization based placement
> since. But I'm not sure if they'd help you.

I'm not sure either. Furthermore I "have to" use packages provided by
the "regular" ubuntu 12.04 repository.