An interesting thought. If you enable graph output in your puppet.conf
http://docs.puppetlabs.com/references/stable/configuration.html#graph
you can identify those sub-graphs that could run in parallel pretty
easily, just by eyeballing it. Parallel execution is wonderful for an
optimizing compiler because you're strongly CPU limited. I'd be
willing to bet that a parallel puppet agent would be of less use: once
the catalog is compiled on the master, puppet's execution time is
going to be limited by network and disk IO. Probably. Running puppet
agent through DTrace/SystemTap would be instructive.
Also, some resources are implicitly exclusive: two Packages with 'apt'
providers cannot be run in parallel because Debian/Ubuntu keeps a
global lock on... hmm, I've forgotten what, exactly. It's there,
though. Ensuring that implicitly parallel resources block one another
would increase the implementation complexity of Puppet, of end-user
modules or, as is likely, both.
Aside from all other considerations, multi-core parallelism in MRI is
not so great. JRuby's better, being hosted on the JVM, but, well,
MRI's RAM consumption is already bad enough.
On Sun, Mar 4, 2012 at 10:53 PM, Jon Forrest <[email protected]> wrote:
> As many learning Puppet for the first time, the fact that the
> order of actions is undefined unless specific metaparameters
> like 'require' are used. Fine.
>
> This got me to thinking. The GNU make program has the "-j"
> option, which allows make to start more than one action
> in parallel if the actions are at the same dependency level.
> I've used this option on a 48-core machine to great benefit.
>
> So, why can't there be a similar option in the puppet agent?
> I can easily imagine how this could substantially reduce the
> length of time for a puppet run.
>
> (The make "-j" option allows an optional numeric value, which, if
> given, is the maximum number of actions that can be run
> in parallel. If no numeric is given, then there's no limit
> to the number of parallel actions).
>
> I did a quick review of the Puppet manual but I didn't see
> anything like this. Am I missing something? Is this a good
> idea?
>
> Cordially,
> Jon Forrest
>
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Brian L. Troutwine
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