On Jul 17, 2009, at 6:08 AM, Burkholder, Peter wrote:
>
> I just finished listening to the Configuration Management panel from
> OSBridge (on blip.tv).
>
> Near the end of it, Adam Jacob states that Puppet's resource
> dependency
> ordering is non-deterministic,
> and that manifests that work fine 19 times will fail the 20th time.
>
> Is this true? I'm puzzled that what Luke considers one of Puppet's
> strong suits is derided by
> others as its Achille's heel.
Dependency ordering is entirely deterministic.
Ordering of unrelated items, just like in any other topological sort
of a graph, is currently nondeterministic.
We could trivially add deterministic ordering for unrelated items:
Just sort any equivalent resources based on name. Ten seconds after
you do this, you'll have people naming resources things like
'00001myservice' because they want to use alphabetic sorting instead
of declared dependencies, and then they'll complain when specified
dependencies get preference.
Basically, once we start saying "unrelated resources will always
happen in a predictable order", we can never change the internal
implementation or add parallelism. There might be some ways to
increase consistency without sacrificing these, but no one besides
Adam has complained much about it, and he was never willing to
actually contribute code to fixing it.
--
It's very hard to predict things . . . Especially the future.
-- Prof. Charles Kelemen, Swarthmore CS Dept.
---------------------------------------------------------------------
Luke Kanies | http://reductivelabs.com | http://madstop.com
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