Another HAMMER crash

[Matthew Dillon]

: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,
:etc.)
:
:Otherwise people will have the impression that hammer's history feature
:needs snapshots, which it does not.
:
:cheers
:  simon
    
    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).

					-Matt
					Matthew Dillon 
					<dillon at backplane.com>