Re: Beagle and logging inotify events

["J. Bruce Fields" <bfields@fieldses.org>]

On Wed, Nov 14, 2007 at 12:32:45PM -0700, Andreas Dilger wrote:
> On Nov 14, 2007  11:32 -0500, Chuck Lever wrote:
> > I disagree: we don't need a "bullet-proof" log.  We can get a significant 
> > performance improvement even with a permanent dnotify log implemented in 
> > user-space.  We already have well-defined fallback behavior if such a log 
> > is missing or incomplete.
> >
> > The problem with a permanent inotify log is that it can become unmanageably 
> > enormous, and a performance problem to boot.  Recording at that level of 
> > detail makes it more likely that the logger won't be able to keep up with 
> > file system activity.
> >
> > A lightweight solution gets us most of the way there, is simple to 
> > implement, and doesn't introduce many new issues.  As long as it can tell 
> > us precisely where the holes are, it shouldn't be a problem.
> 
> Jan Kara is working on a patch for ext4 which would store a recursive
> timestamp for each directory that gives the latest time that a file in
> that directory was modified.  ZFS has a similar mechanism by virtue of
> doing full-tree updates during COW of all the metadata blocks and storing
> the most recent transaction number in each block.  I suspect btrfs could
> do the same thing easily.
> 
> That would allow recursive-descent filesystem traversal to be much more
> efficient because whole chunks of the filesystem tree can be ignored during
> scans.

The problem is that people may not be happy with the random behavior of
hardlinks, right?

--b.