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Re: [Linux-cluster] Lock Resources



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

> Ja S wrote:
> > --- Ja S <jas199931 yahoo com> wrote:
> > 
> >>>> A couple of further questions about the master
> >>> copy of
> >>>> lock resources.
> >>>>
> >>>> The first one:
> >>>> =============
> >>>>
> >>>> Again, assume:
> >>>> 1) Node A is extremely too busy and handle all
> >>>> requests
> >>>> 2) other nodes are just idle and have never
> >>> handled
> >>>> any requests
> >>>>
> >>>> According to the documents, Node A will hold
> all
> >>>> master copies initially. The thing I am not
> >> aware
> >>> of
> >>>> and unclear is whether the lock manager will
> >>> evenly
> >>>> distribute the master copies on Node A to other
> >>> nodes
> >>>> when it thinks the number of master copies on
> >> Node
> >>> A
> >>>> is too many?
> >>> Locks are only remastered when a node leaves the
> >>> cluster. In that case
> >>> all of its nodes will be moved to another node.
> We
> >>> do not do dynamic
> >>> remastering - a resource that is mastered on one
> >>> node will stay mastered
> >>> on that node regardless of traffic or load,
> until
> >>> all users of the
> >>> resource have been freed.
> >>
> >> Thank you very much.
> >>
> >>
> >>>> The second one:
> >>>> ==============
> >>>>
> >>>> Assume a master copy of lock resource is on
> Node
> >>> A.
> >>>> Now Node B holds a local copy of the lock
> >>> resource.
> >>>> When the lock queues changed on the local copy
> >> on
> >>> Node
> >>>> B, will the master copy on Node A be updated
> >>>> simultaneously? If so, when more than one nodes
> >>> have
> >>>> the local copy of the same lock resource, how
> >> the
> >>> lock
> >>>> manager to handle the update of the master
> copy?
> >>> Using
> >>>> another lock mechanism to prevent the
> corruption
> >>> of
> >>>> the master copy?
> >>>>
> >>> All locking happens on the master node. The
> local
> >>> copy is just that, a
> >>> copy. It is updated when the master confirms
> what
> >>> has happened. The
> >>> local copy is there mainly for rebuilding the
> >>> resource table when a
> >>> master leaves the cluster, and to keep a track
> of
> >>> locks that exist on
> >>> the local node. The local copy is NOT complete.
> it
> >>> only contains local
> >>> users of a resource.
> >>>
> >> Thanks again for the kind and detailed
> explanation. 
> >>
> >>
> >> I am sorry I have to bother you again as I am
> having
> >> more questions. I analysed /proc/cluster/dlm_dir
> and
> >> dlm_locks and found some strange things. Please
> see
> >> below:
> >>
> >>
> >> >From /proc/cluster/dlm_dir:
> >>
> >> In lock space [ABC]:
> >> This node (node 2) has 445 lock resources in
> total
> >> where
> >> --328   master lock resources
> >> --117   local copies of lock resources mastered
> on
> >> other nodes.
> >>
> >> ===============================
> >> ===============================
> >>
> >>
> >> >From /proc/cluster/dlm_locks:
> >>
> >> In lock space [ABC]:
> >> There are 1678 lock resouces in use where
> >> --1674  lock resources are mastered by this node
> >> (node
> >> 2)
> >> --4     lock resources are mastered by other
> nodes,
> >> within which:
> >> ----1 lock resource mastered on node 1
> >> ----1 lock resource mastered on node 3
> >> ----1 lock resource mastered on node 4
> >> ----1 lock resource mastered on node 5
> >>
> >> A typical master lock resource in
> >> /proc/cluster/dlm_locks is:
> >> Resource 000001000de4fd88 (parent
> 0000000000000000).
> >> Name (len=24) "       3         5fafc85"
> >> Master Copy
> >> LVB: 01 16 19 70 00 00 ff f8 00 00 00 00 00 00 00
> 00
> >>      00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 00
> >> Granted Queue
> >> 1ff5036d NL Remote:   4 000603e8
> >> 80d2013f NL Remote:   5 00040214
> >> 00240209 NL Remote:   3 0001031d
> >> 00080095 NL Remote:   1 00040197
> >> 00010304 NL
> >> Conversion Queue
> >> Waiting Queue
> >>
> >>
> >> After search for local copy in
> >> /proc/cluster/dlm_locks, I got:
> >> Resource 000001002a273618 (parent
> 0000000000000000).
> >> Name (len=16) "withdraw 3......"
> >> Local Copy, Master is node 3
> >> Granted Queue
> >> 0004008d PR Master:     0001008c
> >> Conversion Queue
> >> Waiting Queue
> >>
> >> --
> >> Resource 000001003fe69b68 (parent
> 0000000000000000).
> >> Name (len=16) "withdraw 5......"
> >> Local Copy, Master is node 5
> >> Granted Queue
> >> 819402ef PR Master:     00010317
> >> Conversion Queue
> >> Waiting Queue
> >>
> >> --
> >> Resource 000001002a2732e8 (parent
> 0000000000000000).
> >> Name (len=16) "withdraw 1......"
> >> Local Copy, Master is node 1
> >> Granted Queue
> >> 000401e9 PR Master:     00010074
> >> Conversion Queue
> >> Waiting Queue
> >>
> >> --
> >> Resource 000001004a32e598 (parent
> 0000000000000000).
> >> Name (len=16) "withdraw 4......"
> >> Local Copy, Master is node 4
> >> Granted Queue
> >> 1f5b0317 PR Master:     00010203
> >> Conversion Queue
> >> Waiting Queue
> >>
> >> These four local copy of lock resources have been
> >> staying in /proc/cluster/dlm_locks for several
> days.
> >>
> >> Now my questions:
> >> 1. In my case, for the same lock space, the
> number
> >> of
> >> master lock resources reported by dlm_dir is much
> >> SMALLER than that reported in dlm_locks. My
> >> understanding is that master lock resources
> listed
> >> in
> >> dlm_dir must be larger than or at least the same
> as
> >> that reported in dlm_locks. The situation I
> >> discovered
> >> on the node does not make any sense to me. Am I
> >> missing anything? Can you help me to clarify the
> >> case?
> > 
> > I have found the answer. Yes, I did miss
> something. I
> > need to sum all lock resources mastered by the
> node on
> > all cluster members. In this case, the total
> number of
> > lock resources mastered by the node is just 1674,
> > which matches the number reported from dlm_locks.
> > Sorry for asking the question without careful
> > thinking.
> > 
> > 
> >> 2. What can cause "withdraw ...." to be the lock
> >> resource name? 
> > 
> > After read the gfs source code, it seems that this
> is
> > caused by issuing a command like "gfs_tool
> withdraw
> > <mountpoint>". However, I checked all command
> > histroies on all nodes in the cluster, but did not
> > find any command like this. This question and the
> next
> > question remain open. Please help.
> 
> 
> You might like to ask GFS-specific questions on a
> new thread. I don't
> know about GFS and the people who do are probable
> not reading this one
> by now ;-)
> 
> 
> >> 3. These four local copy of lock resources have
> not
> >> been released for at least serveral days as I
> knew.
> >> How can I find out whether they are in a strange
> >> dead
> >> situation or are still waiting for the lock
> manager
> >> to release them? How to change the timeout?
> 
> There is no lock timeout for local copies. If a lock
> is shown in
> dlm_locks then either the lock is active somewhere
> or you have found a bug!
> 
> Bear in mind that this is a DLM response, GFS does
> cache locks but don't
> know the details.
> 


Thank you for the information.

Best,

Jas


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