[Gluster-users] [Gluster-devel] Re: AFR documentation

[Martin Fick]

--- On Thu, 12/18/08, Amar S. Tumballi <amar at zresearch.com> wrote:

> This was put on
> http://ftp.zresearch.com/pub/gluster/glusterfs/doc/ sometime
> back.


Wow, that is some really neat/impressive functionality that has been added to AFR!  That document was very useful in explaining much of the new functionality, thank you.

I have some questions about things that were perhaps implied in the document, but not really discussed.  It sounds like the 5 step write process lays the foundations for transaction based writes and efficient self healing?  I am curious how many of the failures cases are currently dealt with besides the mentioned split brain problems.  Are there any rollback procedures implemented?  It seems likely the intent, I am just trying to clarify the current functionality.  

For example:  what happens if the client dies between step 2 and 3?  The client has 1. locked file (or directory) on all of the lock servers and
2. written the change log entries on all servers, and then dies.  Will the lock timeout?  If so, does another client then know how to (is it capable of) either complete the write or roll it back at this point?  What if the client failure occurs after or during any of the other steps, can the entire process be either moved forward or rolled back (yet)?  With this 5 step process, it seems like a guaranteed rollback should be possible anytime before step 3 and a commit should be possible anytime after step 2 (even if only completed on one server).  Is that correct?

Thanks,

-Martin