Xapian discuss - Nov 2009 - Questions about the "Atomic modifications" of xapian

Hi, all:

    I read the "Xapian Administrator's Guide" and it says in the
"Atomic
modifications" section:

    """
    If the system is interrupted during a modification, the database should
always be left in a valid state. This applies even if the power is cut
unexpectedly, as long as the disk does not become corrupted due to hardware
failure.
    """

    I want to know how xapian could guarantee this. I cannot found answer on
the web.
    Could anyone can give some explaination?

-- 
Best wishes from Ray ...

On Thu, Nov 12, 2009 at 06:03:38PM +0800, ?????????
wrote:
>     """
>     If the system is interrupted during a modification, the database should
> always be left in a valid state. This applies even if the power is cut
> unexpectedly, as long as the disk does not become corrupted due to hardware
> failure.
>     """
> 
>     I want to know how xapian could guarantee this. I cannot found answer
on
> the web.
The B-tree manager supports versioning, so updates are made to a new version of
the tree which isn't made "current" until we want to commit it.

See http://xapian.org/docs/internals.html for some more information, and the
source code in backends/flint (or backends/chert for trunk, though it is pretty
similar in this regard) for the gory details.

Cheers,
    Olly