On Tue, Jul 15, 2008 at 01:41:25PM -0700, Sage Weil wrote: > On Tue, 15 Jul 2008, J. Bruce Fields wrote: > > > - There is some built-in delay before statistics fully propagate up > > > toward the root of the hierarchy. Changes are propagated > > > opportunistically when lock/lease state allows, with an upper bound of (by > > > default) ~30 seconds for each level of directory nesting. > > > > That makes it less useful, e.g., for somebody with cached data trying to > > validate their cache, or for something like git trying to check a > > directory tree for changes. > > Having fully up to date values would definitely be nice, but unfortunately > doesn't play nice with the fact that different parts of the directory > hierarchy may be managed by different metadata servers. A primary goal in > implementing this was to minimize any impact on performance. The uses I > had I mind were more in line with quota-based accounting than cache > validation. Fair enough. > I think I can adjust the propagation heuristics/timeouts to make updates > seem more or less immediate to a user in most cases, but that won't be > sufficient for a tool like git that needs to reliably identify very recent > updates. For backup software wanting a consistent file system image, it > should really be operating on a snapshot as well, in which case a delay > between taking the snapshot and starting the scan for changes would allow > those values to propagate. > > > > - Ceph internally distinguishes between multiple links to the same file > > > (there is a single 'primary' link, and then zero or more 'remote' links). > > > Only the primary link contributes toward the 'rbytes' total. > > > > Is that only true for 'rbytes'? > > The same goes for rctime. As far as the recursive stats go, the other > stats (file/directory counts) aren't affected. The primary/remote > hard link distinction is fundamental to the way metadata is internally > managed and stored by the MDS, though, if that's what you mean (inode > content is embedded with the primary link's directory metadata). I just wonder how one would explain to users (or application writers) why changes to a file are reflected in the parent's rctime in one case, and not in another, especially if the primary link is otherwise indistinguishable from the others. The symptoms could be a bit mysterious from their point of view. --b. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
