[tahoe-dev] Tahoe Lock Files vs. K = 1
zooko at zooko.com
Wed Mar 5 12:36:21 PST 2008
Yesterday Brian came up with an excellent hack to solve the problem
of mutable files being destroyed -- all of their old and new versions
destroyed -- by uncoordinated writes. The solution is simply: set K
The problem with uncoordinated writes is that some storage servers
can end up with one version of the file and other storage servers can
end up with another version. This isn't fatal -- you can always
retrieve at least one, if not both, version later. But what is fatal
is if no version has enough shares in existence to be reconstructed.
For example, suppose K = 3, and there are six servers, and two
servers have shares from version 1, two servers have version 2, and
two servers have version 3. This is the case where all versions of
the file can be permanently lost.
So, yesterday, Brian said "How about just setting K = 1 for small
distributed mutable files?", and solved the problem at a stroke.
It does mean that mutable files take up a bit more space that
immutable ones do, but mutable files are intended to be used only for
relatively small things anyway.
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