On Mon, Nov 29, 2010 at 02:49:26PM -0500, David Teigland wrote:
On Wed, Nov 24, 2010 at 03:08:41PM -0500, David Teigland wrote:
> LOCK_MODE_NONE - the lock manager is unused, and it's up to the
> application to do its own locking or coordination when accessing the
> resource, e.g. if there's a clustered db or fs on the device that does its
> own coordination. You seem to be calling this SHARED, but there's
> actually no lock or exclusion that a lock manager would implement for this
> kind of usage.
I failed to mention that with a more elaborate set of lock modes like a
dlm uses, the CW "concurrent write" mode fits the use case of leaving the
coordination to the application. Simpler lock managers only support
Shared or Exclusive, of course, in which case "None" would apply.
This kind of difference in capabilities between lock managers is a good
example of why I only provide the disk sharing mode to the plugin API,
and leave choice of locking mode to the plugin.
Daniel