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I can see how this would be theoretically possible in the same way I could see using `git filter-branch` to remove one or more commits from a code repository. But as it requires walking back up the tree to recalculate all of the commit hashes based on the new state of your files, I suspect it would be an extremely slow/expensive operation in bup's case. Someone who knows more about bup's internals can correct me if I'm wrong.

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true. and actually bup can't use git's tooling directly because of the different use cases it's optimized for. git won't make any use of bup's optimizations: midx (combination of multiple .idx files into a handful of bigger ones to reduce page faults during binary searches) and bloom filter.

git's tools, namely filter-branch and gc have been reported to work on limited-size bup repositories, but it very quickly eats up all ram and cpu and never finishes because of the sheer amount of objects that are usually stored in a bup repository

Isn't this exactly what Obnam does?

I suspect that Obnam doesn't cause all of the de-duplicated chunks to get so "entagled" (as bup puts it, in their readme).

There are existing discussions about the way bup pruning would have to work:

https://groups.google.com/forum/#!searchin/bup-list/prune/bu...

Sounds like they are actually making progress on it.

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