[Gluster-devel] Proposal to change locking in data-self-heal

[Stephan von Krawczynski]

On Tue, 21 May 2013 09:10:18 -0400 (EDT)
Pranith Kumar Karampuri <pkarampu at redhat.com> wrote:

> [...]
> Solution:
> Since we want to prevent two parallel self-heals. We let them compete in a separate "domain". Lets call the domain on which the locks have been taken on in previous approach as "data-domain".
> 
> In the new approach When a self-heal is triggered it
> acquires a full lock in the new domain "self-heal-domain".
>     After this it performs data-self-heal using the locks in "data-domain" in the following manner:
>     Acquire full file lock and get xattrs on file and decide source/sinks unlock full file lock.
>     acquire lock with range 0 - 128k, sync the data from source to sinks in range 0 - 128k unlock 0 - 128k lock.
>     acquire lock with range 128k+1 - 256k, sync the data from source to sinks in range 128k+1 - 256k, unlock 128k+1 - 256k lock.
>     .....
>     until the end of file is reached do this.
>     acquire full file lock and decrement the pending counts then unlock the full file lock.
> unlock the full file lock in "self-heal-domain"
> 
> scenario-1 won't happen because there exists a chance for it to acquire truncate's full file lock after any 128k range sync happens.
> Scenario-2 won't happen because extra self-heals that are launched on the same file will be blocked in self-heal-domain so the data-path's locks are not affected by this.
> 
> Let me know if you see any problems/suggestions with this approach.
> 
> Pranith.

I am not quite sure if I understood the issue in full detail. But are you
saying that you "split up" the current self-healing file in 128K chunks with
locking/unlocking (over the network)?
It sounds a bit like the locking takes more (cpu) time than the self-healing
of the data itself. I mean this can be a 10 G link where a complete file could
be healed in almost no time, even if the file is quite big.
Sure WAN is different, but I really would like to have at least an option to
drop the partial locking completely and lock the full file instead.

-- 
Regards,
Stephan