Re: Hammer: Transactional file updates

[Jasse Jansson <jasse@xxxxxxxxxxxxx>]

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