Re: Beagle and logging inotify events

["Jon Smirl" <jonsmirl@gmail.com>]

On 11/14/07, J. Bruce Fields <bfields@fieldses.org> wrote:
> On Wed, Nov 14, 2007 at 04:30:16PM +0100, Andi Kleen wrote:
> > "Jon Smirl" <jonsmirl@gmail.com> writes:
> >
> > > On 11/14/07, Chuck Lever <chuck.lever@oracle.com> wrote:
> > >> On Nov 13, 2007, at 7:04 PM, Jon Smirl wrote:
> > >> > Is it feasible to do something like this in the linux file system
> > >> > architecture?
> > >> >
> > >> > Beagle beats on my disk for an hour when I reboot. Of course I don't
> > >> > like that and I shut Beagle off.
> > >>
> > >> Leopard, by the way, does exactly this: it has a daemon that starts
> > >> at boot time and taps FSEvents then journals file system changes to a
> > >> well-known file on local disk.
> > >
> > > Logging file systems have all of the needed info.
> >
> > Actually most journaling file systems in Linux use block logging and
> > it would be probably hard to get specific file names out of a random
> > collection of logged blocks. And even if you could they would
> > hit a lot of false positives since everything is rounded up
> > to block level.
> >
> > With intent logging like in XFS/JFS it would be easier, but even
> > then costly :- e.g. they might log changes to the inode but
> > there is no back pointer to the file name short of searching the
> > whole directory tree.
>
> So it seems the best approach given the current api's would be just to
> cache all the stat data, and stat every file on reboot.
>
> I don't understand why beagle is reading the entire filesystem data.  I
> understand why even just doing the stat's could be prohibitive, though.

I believe Beagle is looking at the mtimes on the files. It uses xattrs
to store the last mtime it checked and then compares it to the current
mtime. It also stores a hash of the file in an xattr. So even if the
mtimes don't match it recomputes the hash and only if the hashes
differ do it update its free text search index.

>
> --b.
>


-- 
Jon Smirl
jonsmirl@gmail.com