Bug 618303

Description of problem:

plock_ownership is an alternative, more complex, plock protocol in
dlm_controld that optimizes for a certain pattern of locking by
applications.

In RHEL5, plock_ownership defaults to 0 (off), and in RHEL6 it defaults to
1 (on).  on is more complicated and QE is still finding problems, i.e. off
is going to result in less customer problems.

Assuming both modes work correctly, neither is always a better choice.

on optimizes the case of repetitious locking of the same mostly unshared
(across nodes) files, at the expense of complexity and extra messages when
nodes are locking the same files.

off optimizes for the case of nodes generally acquiring locks on the same
files, at the expense of extra messages when nodes repeatedly lock their
own files that other nodes don't access.

At the beginning of RHEL6 development, we switched the default to on,
assuming, I suppose, that the new optimization would be an improvement
for most people, but I don't think that has been the case.

plock_ownership is one of the settings that cannot be changed online; the cluster needs to be stopped to change it.  This means it is not as quick and simple for people to change if they have problems with it, and it also means we cannot change the default setting in an update release.

Regarding the testing of the two modes, all (or most) RHEL5 testing has been done with it off, and this is substantially more testing than RHEL6 testing thus far with it on.  (The plock code is the same in RHEL5 and RHEL6, it's just the default protocol has changed.)

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