[Linux-cluster] What is the order of processing a lock request?

[Ja S]

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

> Ja S wrote:
> > --- Christine Caulfield <ccaulfie at redhat.com>
> wrote:
> > 
> >> Ja S wrote:
> >>> Hi, All:
> >>>
> >>>
> >>> When an application on a cluster node A needs to
> >>> access a file on a SAN storage, how DLM process
> >> the
> >>> lock request? 
> >>>
> >>> Should DLM firstly determine whether there
> already
> >>> exists a lock resource mapped to the file, by
> >> doing
> >>> the following things in the order 1) looking at
> >> the
> >>> master lock resources on the node A, 2)
> searching
> >> the
> >>> local copies of lock resources on the node A, 3)
> >>> searching the lock directory on the node A to
> find
> >> out
> >>> whether a master lock resource assosicated with
> >> the
> >>> file exists on another node, 4) sending messages
> >> to
> >>> other nodes in the cluster for the location of
> the
> >>> master lock resource? 
> >>>
> >>> I ask this question because from some online
> >> articles,
> >>> it seems that DLM will always search the
> >> cluster-wide
> >>> lock directory across the whole cluster first 
> to
> >> find
> >>> the location of the master lock resource. 
> >>>
> >>> Can anyone kindly confirm the order of processes
> >> that
> >>> DLM does?
> >>>
> >>
> >> This should be very well documented, as it's
> common
> >> amongst DLM
> >> implementations.
> >>
> > 
> > I think I may be blind. I have not yet found a
> > document which describes the sequence of processes
> in
> > a precise way. I tried to read the source code but
> I
> > gave up due to lack of comments.
> > 
> > 
> >> If a node needs to lock a resource that it
> doesn't
> >> know about then it
> >> hashes the name to get a directory node ID, than
> >> asks that node for the
> >> master node. if there is no master node (the
> >> resource is not active)
> >> then the requesting node is made master
> >>
> >> if the node does know the master, (other locks on
> >> the resource exist)
> >> then it will go straight to that master node.
> > 
> > 
> > Thanks for the description. 
> > 
> > However, one point is still not clear to me is how
> a
> > node can conclude whether it __knows__ the lock
> > resource or not?
> 
> A node knows the resource if it has a local copy.
> It's as simple as that.
> 

If the node is a human and has a brain, it can
"immediately" recall that it knows the lock resouce.
However, for a computer program, it does not "know"
anything until it search the target in what it has on
hand.

Therefore, the point here is the __search__. What
should the node search and in which order, and how it
searches?

If I missed anything, please kindly point out so that
I can clarify my question as clear as possible.


Thanks again for your time and kind reply.

Jas
> 
> 
> -- 
> 
> Chrissie
> 
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