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note on cycles

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Joey Hess 2024-05-02 12:22:04 -04:00
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doc/design/passthrough_proxy.mdwn
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@ -187,6 +187,28 @@ implementation for this.
There's potentially a layering problem here, because exactly how encryption
(or chunking) works can vary depending on the type of special remote.
## cycles
What if repo A is a proxy and has repo B as a remote. Meanwhile, repo B is
a proxy and has repo A as a remote?
An upload to repo A will start by checkin if repo B wants the content and if so,
start an upload to repo B. Then the same happens on repo B, leading it to
start an upload to repo A.
At this point, it might be possible for git-annex to detect the cycle,
if the proxy uses a transfer lock file. If repo B or repo A had some other
remote that is not part of a cycle, they could deposit the upload there and
the upload still succeed. Otherwise the upload would fail, which is
probably the best that can be done with such a broken configuration.
So, it seems like proxies will need to take transfer locks for uploads,
even though the content is being proxied to elsewhere.
Dropping could have similar cycles with content presence locking, which
needs to be thought through as well. A cycle of the actual dropContent
operation might also be possible.
## exporttree=yes
Could the proxy be in front of a special remote that uses exporttree=yes?