DragonFly bugs List (threaded) for 2008-07
Re: Another HAMMER crash
:I think we should have a way to specify fuzzy values like "yesterday", "10
:minutes ago" or even "previous" (call it "-1", "-2" for the one before,
:Otherwise people will have the impression that hammer's history feature
:needs snapshots, which it does not.
I originally had that sort of feature but I ripped it out because
the moving target got really confusing.
There is another issue here and that is the filesystem is only
guaranteed to be consistent on snapshot boundaries. This will be
true for all fine-grained history, but once you prune the filesystem
anything older then the most recent snapshot softlink really has to
be accessed via a softlink, or at least a transaction id that exists
in a softlink (one of the softlinks that the prune code was told to
retain). If you use a random transaction id you will get an
inconsistent version of the filesytem.
The reason is that pruning operations create holes in the history in
those areas it was told to prune. If you try to access the filesystem
in those areas you will get a combination of records and holes.
Originally the pruning code fixed up the B-Tree records to cover the
holes but I decided that was too dangerous to do, and it also made
mirroring impossible (becaused fixed historical records were being
modified by the pruning code).