[Xapian-discuss] backing up a database by locking while backup program runs

[James Aylett]

On Thu, Dec 13, 2007 at 05:52:44PM +0000, Ronan wrote:

> I want to back up a Xapian database.  If I copy the database directory
> and its contents using (for instance) rsync, and I know that throughout
> the duration of the rsync process another process has had the database
> open for writing, but has not actually made any modifications, can I
> be sure that, on completion of the rsync process, I have a copy of the
> database which is consistent and fully up-to-date?

Providing all changes were flushed before you started the rsync, and
no changes have happened since then, you're fine.

> The document at [1] makes it fairly clear that the answer is "Yes",
> but I'm a little doubtful about the status of that document, since there
> seem to be no links to it from the Xapian website.  (The following Google
> query finds nothing: "link:www.xapian.org/docs/admin_notes.html".)
> 
> [1] http://www.xapian.org/docs/admin_notes.html

We should link that in somewhere, but all those docs are distributed
as part of the core library, so it's an official document you can
depend on. (And similarly, if you find a problem, please let us know! :-)

> I propose to use a simple PHP script like the following in order to
> obtain the write lock:
> 
>   <?php 
>   $h = new XapianWritableDatabase("/my/Xapian/database", DB_OPEN);
>   sleep(99999);

Better would be to spawn the rsync from within the PHP script, if you
can manage it (might require some ssh funkiness). That way you can't
eg background the rsync and have the lock released while it's still
running.

J

-- 
/--------------------------------------------------------------------------\
  James Aylett                                                  xapian.org
  james at tartarus.org                               uncertaintydivision.org