[Linux-cluster] DLM

[Daniel Phillips]

Hi Patricio,

I'll take a run at answering this, since the DLM engineers are in far 
away timezones.

On Thursday 17 March 2005 16:39, Patricio Bruna V wrote:
> how does dlm comunicates with the other nodes?

It uses a custom-made network protocol called PF_CLUSTER, which is 
nominally part of cman.  This protocol is similar to UDP but with 
delivery (and ordering?) guarantees. 

> how dlm ask for a lock?

The short answer: DLM does not ask for locks.  DLM is the boss and takes 
locks as it sees fit.

Perhaps you meant, how does your program ask for a lock?  Or how does 
DLM get a lock from a nonlocal machine?  From userspace, you go through 
a library that presents an interface similar to ancient Vaxcluster, and 
later, IBM's OpenDLM.  (But somewhat more complex because of the 
hierarchical locks feature and a few other wrinkles.)  These API calls 
are translated into socket messages to and from the in-kernel DLM.  The 
local DLM consults its lock directory to find out which machine masters 
the lock and requests the lock from that machine, which then tries to 
get the lock based on its knowledge of current holders, if any.

Does that answer your question?

> im asking this because i want to know what happens if dlm comunicates
> trough the LAN (or crossover) and need to ask for a stupid amount of
> locks (like 10000000) and the lan (or crossover ) its fully loaded
> with other kind of traffic

Try it and see what breaks :-)

Regards,

Daniel