On 6/4/2010 1:03 PM, Trevor Vaughan wrote:
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Completely agree with the issue of lock contention.
You would probably have to provide the capability to have optional lock
overrides or timeouts.
So...something like:
# Grab a semaphore for the '$dataserver/bar' data
# Timeout after 5 seconds
# Skip requiring stanza if lock cannot be obtained.
semaphore { "$dataserver/bar":
timeout => '5',
fail_mode => 'skip'
}
lock(Semaphore["$dataserver/bar"]) {
...do fancy stuff...
}
I'm not convinced that this should be handled client side. And I'm
pretty sure you'd want to use the existing require/before syntax to
specify the dependencies on locks.
Best Regards, David
Trevor
On 06/04/2010 04:33 AM, David Schmitt wrote:
On 6/3/2010 3:54 AM, Trevor Vaughan wrote:
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I've been following this thread with interest and I think that Donavan
is hitting upon something that I've also been wanting.
However, the way I was looking at it was as a set of atomic, optionally
blocking, semaphores in a set of parallel threads.
If you look at each puppet client as an individual thread and realize
that you need things to happen cross-client that depend on the state of
one or more clients, then you've deconstructed this into a classic
parallel programming application (with all the constituent nonsense).
Interesting perspective! Especially as this allows one to re-use the
existing research to evaluate the pitfalls of such an approach.
Deadlocks can be circumvented by partially aborting transactions (i.e.
failing dependend resources) instead of locking.
Serializability is not really a concern of puppet, since we have
eventual convergence.
A more complex problem in our case would be contention of locks (e.g.
when used for orchestrating a N-out-of-M rollout). I'm thinking of
thundering herd problems or often repeated and aborted transactions.
Best Regards, David
- --
Trevor Vaughan
Vice President, Onyx Point, Inc.
email: [email protected]
phone: 410-541-ONYX (6699)
pgp: 0x6C701E94
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