Hammer: Transactional file updates

[Jasse Jansson]

On Aug 1, 2008, at 1:09 PM, Michael Neumann wrote:

Hi,

So Hammer does not guarantee "transctional consistency" of data in  
case
of a crash, only that of meta-data, right?

Is there a method to guarantee the write to be transactional, so that
I either have the previous "version" of the file or the version that I
wrote? Like this:
  fd = open(file);  // behaves like START TRANSACTION
  read(fd, ...);
  write(fd, ...);
  close(fd);        // behaves like COMMIT
That would be incredible cool (and very useful!) and could play  
well due
to Hammers historical nature.
You are talking about COW (copy on write), right.
It slows things down, but it's cool.
BTW, I think Netapp sued Sun for implementing that in ZFS,
but I don't know the end of that story.




Kaiser Jasse -- Authorized Stealth Oracle

The axioms of wisdom:
1. Go the SPARC way of life
2. You can't conquer the universe without the knowledge of FORTRAN
3. In the Unix realm, 10% of work fixes 90% of the problems