On Tue, 2004-11-30 at 14:16 -0600, Chris Adams wrote: > Once upon a time, Neal D. Becker <ndbecker2@xxxxxxxxxxx> said: > > Are you sure? What if you: > > 1) duplicate the directory (using hardlinks to files) > > 2) atomic rename directory > > You can't do step #2. You can only rename over an existing directory if > the directory is already empty. > > The only way you can do something like what you say is if you create the > directories under a different name and use symlinks to point to them > (you can replace a symlink atomically by creating a new symlink under a > new name and then renaming the symlink over the old one). Would this actually be atomic? What if two apps tried doing this at once? One makes db-1 as the temp work directory, another makes db-2 as the temp dir, and then whoever makes the symlink last gets the symlink pointing to their data, resulting in the previous process' changes being silently lost. You'd have to do locking, which I noted the problems with (NFS in particular) in my other mail. Or, if Elektra were to use a daemon that centralizes access, you wouldn't need the locking (only one process doing this at a time), but Elektra won't do that for several sort-of-almost good reasons of early bootup. (I suppose if the DB is read-only you can do without the daemon, and early bootup probably would be read-only, so you can have Elektra start the daemon later on, but I'm not sure how well that would work either - yet more race conditions between apps reading something when the daemon starts and potentially starts changing stuff.) > > If you go that way, you have to have a clean-up program. Otherwise, > unclean shutdowns (either of the management program(s) or of the system) > will leave stuff all over the place. You could use a log to make the > clean-up faster, and rotate the log out when it is processed (i.e. along > the lines of db_checkpoint and db_archive from BDB). > > -- > Chris Adams <cmadams@xxxxxxxxxx> > Systems and Network Administrator - HiWAAY Internet Services > I don't speak for anybody but myself - that's enough trouble. > -- Sean Middleditch <elanthis@xxxxxxxxxxxxxxx> AwesomePlay Productions, Inc.
