Revfile vs Atomicity & Dumbfs

[Robert Collins]

dumbfs is one of the things I believe arch got spot on : it works well
pushing to FTP/webDAV/sftp servers with no process executing on the
other side of the link.

The tradeoffs for this include a pretty low GCD - no appending to
existing files, locking by directory renames. This means that
incremental data is uploaded to a new dir, which is then renamed into
place. This is very robust, but has two rather significant costs:

* round trips for retrieval are proportional to history length, not to
the number of files under control. (This is mitigated by full-text
copies, but that only goes so far).
* many-small-files problem.

I think that the former can be mitigated much better than tla does
today, and I think that bzr should have an optional storage format that
works on a dumbfs basis - but that the default should be the much more
efficient revfile approach that is under development.

Rob

-- 
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