Re: precise characterization of ext3 atomicity

[Antonio Vargas]

On Thu, Sep 04, 2003 at 11:15:40AM -0700, Mike Fedyk wrote:
> On Thu, Sep 04, 2003 at 08:25:18PM +0400, Hans Reiser wrote:
> > In data=journal and data=ordered modes ext3 also guarantees that the 
> > metadata will be committed atomically with the data they point to.  However 
> > ext3 does not provide user data atomicity guarantees beyond the scope of a 
> > single filesystem disk block (usually 4 kilobytes).  If a single write() 
> > spans two disk blocks it is possible that a crash partway through the write 
> > will result in only one of those blocks appearing in the file after 
> > recovery.
> 
> And how does reiser4 do this without changing the userspace apps?

It won't.


[ snip ] 
> Most files are written with several write() calls, so even if each call is
> atomic, your entire file will not be there.
> 
> Also, ext3 could claim the same atomicity if it only updated meta-data on
> write() call boundaries, instead of block boundaries.

There will be a new API to support userspace-controlled
multifile transactions.

At first stab, multifile transactions will be used internally to
implement extended attributes.

Now, another question is.. will the transaction API support commit() and
rollback()? *grin*

(wonder about coding a simple transactional database with
 shell scripts ;)

-- 
winden/network

1. Dado un programa, siempre tiene al menos un fallo.
2. Dadas varias lineas de codigo, siempre se pueden acortar a menos lineas.
3. Por induccion, todos los programas se pueden
   reducir a una linea que no funciona.
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