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Thanks a lot for your help!This is the same question I had many years ago when I first heard about persistent locking. As I have said before, a particular implementation of persistent locking was used to implement a cluster file system.
From what I remember (It has been more than 4 years since I workedon this). As it was explained to me, the whole point of persistent locks was that the application did not want to keep a bunch of locks open to be able to find out that some event has occurred which would require an application recovery before using the lock. Previously, the application would keep the locks open and if it got a invalid value block back, it would know that a recovery is required. With "persistent" locks, the application did not have to keep the lock open, but would still get the invalid value block if process holding the lock died or a node died.
Re-reading the trucluster man pages I pointed to before (like this one): http://h30097.www3.hp.com/docs/cluster_doc/cluster_16/MAN/MAN3/0021____.HTM
This implementation seems much more complicated than what I remember. This looks like this DLM does keep persistent locks around if they are invalid after the process closes them (and they get marked invalid if a node dies). Thus, a new lock request will see the invalid lock even when all previous users have gone away. I'm guessing that is what is meant by persistent.
The more simple implementation approach I remember (as best as I can -- at least for the node death case anyway -- and it really isn't that simple). If a node dies, then all new persistent locks would return invalid until the dlm_rd_validate() is made. Also, existing dlm locks could get marked invalid during dlm recovery.
This implementation was then used to implement CFS. Recovery went
something like:
running nomally
node dies
DLM recovery runs - non-persistent locks recover
persistent locks return invalid
deadman locks from dead node(s) for each file system are granted
start file system recovery:
surviving nodes pick one to run log replay
id = dlm_attach()
replay file system log
if validate(id) == MORE_RECOVERY
re-start file system recovery
since there's been another death
dlm_validate(id) - persistent locks valid now
other surviving nodes wait for replay
file system recovery complete
if another node dies in the middle of file system recovery
abort current recovery and start over
This is simpler because persistent locks returned invalid based on whether a node died until the validate call was made. Every node in the cluster did not have to replicated each lock information.
The use of persistent locks prevented surviving nodes from accessing metadata BEFORE file system log replay had finished. We used separate lock domains for each file system, so file system recovery happened in parallel.
Sorry for rambling, but I think I answered the question in there
somewhere.
Best Reagrds, Stan
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{E1390A7F:3AD1 1B0C 2019 E183 0CFF 55E8 369A 8B75 E139 0A7F}