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Re: [Linux-cluster] Lock Resources



--- Christine Caulfield <ccaulfie redhat com> wrote:

> Ja S wrote:
> > --- Christine Caulfield <ccaulfie redhat com>
> wrote:
> > 
> > 
> >>> DLM lockspace 'data'
> >>>        5         2f06768 1
> >>>        5          114d15 1
> >>>        5          120b13 1
> >>>        5         5bd1f04 1
> >>>        3          6a02f8 2
> >>>        5          cb7604 1
> >>>        5          ca187b 1
> >>>
> >> The first two numbers are the lock name. Don't
> ask
> >> me what they mean,
> >> that's a GFS question! (actually, I think inode
> >> numbers might be
> >> involved) The last number is the nodeID on which
> the
> >> lock is mastered.
> > 
> > 
> > Great, thanks again!
> > 
> > 
> >>>> That lookup only happens the first time
> >>>> a resource is used by a node, once the
> >>>> node knows where the master is, 
> >>>> it does not need to look it up again,
> >>>> unless it releases all
> >>>> locks on the resource.
> >>>>
> >>> Oh, I see. Just to further clarify, does it
> means
> >> if
> >>> the same lock resource is required again by an
> >>> application on the node A, the node A will go
> >> straight
> >>> to the known node (ie the node B) which holds
> the
> >>> master previously, but needs to lookup again if
> >> the
> >>> node B has already released the lock resource?
> >> Not quite. A resource is mastered on a node for
> as
> >> long as there are
> >> locks for it. If node A gets the lock (which is
> >> mastered on node B) then
> >> it knows always to go do node B until all locks
> on
> >> node A are released.
> >> When that happens the local copy of the resource
> on
> >> node A is released
> >> including the reference to node B. If all the
> locks
> >> on node B are
> >> released (but A still has some) then the resource
> >> will stay mastered on
> >> node B and nodes that still have locks on that
> >> resource will know where
> >> to find it without a directory lookup.
> >>
> > 
> > Aha, I think I missed another important concept --
> a
> > local copy of lock resources. I did not realise
> the
> > existence of the local copy of lock resources.
> Which
> > file should I check to figure out how many local
> > copies a node has and what the local copies are? 
> 
> All the locks are displayed in
> /proc/cluster/dlm_locks, that shows you
> which are local copies and which are masters.


Fantastic !

Thank you very much once more.

Jas




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