[Pacemaker] (LRMD|PCMK)_MAX_CHILDREN?

[Lars Marowsky-Bree]

On 2013-09-12T16:56:35, Andrew Beekhof <andrew at beekhof.net> wrote:

> > The most directly equivalent solution would be to number the per-node
> > in-flight operations similar to what migration-threshold does. (I think
> > we can safely continue to treat all resources as equal to start with.)
> Agreed.  Perhaps even repurpose/rename migration-threshold for the task?
> Or is this typically set much lower than max children?

It's typically set lower, because migration speed degrades if the
network becomes overloaded.

Also, it's slightly different - "migrate_to" already affects the target
node, while "migrate_from" still affects the source still.

I think "migrate" is a valid special case, though I think probably some
code can be shared - so should the need arise to limit, say, specific
ops of specific types in the future, it can be added in easily. But I
really don't want to give them that much rope to start with ;-)

But we could introduce a name change (while still accepting the existing
one to remain backwards-compatible) to be more consistent.

1. Global property: operations-limit, operations-limit-migrate (alias
				      for migration-threshold)
2. Can be overriden via a per-node attribute
2.a. How do to that for operations-limit-migrate? Choose the lower of
     the two node's values.

Name might be a bit too long. And 2.a. might be overdoing it, but while
we're at it ... ;-)


This gives me some pain, though, and I'd welcome advise:

> > Though the transition from an environment variable to a CIB node
> > attribute (inherited from a cluster-property, I assume) is going to suck
> > for the upgrade path :-/

The DC can't read the environment variables, and it's not so easy to
feed them back to the DC.

Auto-tuning has a similar problem. The DC just doesn't know the number
of cores (and 2 * cores is the natural default, with migration-threshold
perhaps defaulting to cores / 2). The LRM at least could get that from
the local system (either /proc or sysconfig).

Should we default the global value to the numbers from the current DC if
unset?


Regards,
    Lars

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