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Joey Hess 2025-01-28 11:12:02 -04:00
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[[!comment format=mdwn
username="joey"
subject="""comment 10"""
date="2025-01-28T14:06:41Z"
content="""
Using metadata to store the inputs of computations like I did in my example
above also seems that it would allow the metadata to be changed, which
would change the output when a key gets recomputed.
It might be possible for git-annex to pin down the current state of
metadata (or the whole git-annex branch) and provide the same input to the
computation when it's run again. (Unless `git-annex forget` has caused
that old branch state to be lost..) But it can't fully isolate the program
from all unpinned inputs without using some form of containerization,
which feels out of scope for git-annex.
Instead of using metadata, the input values could be stored in the
per-special-remote state of the generated key. Or the input values could be
encoded in the key itself, but then two computations that generate the same
output would have two different keys, rather than hashing to the same key.
And using a key with a regular hash backend lets the user find out if the
computation turns out to not be reproducible later for whatever reason;
getting the file from the compute special remote will fail at hash
verification time. Something like a VURL key could still alternatively be
used in cases where reproducibility is not important.
To add a computed file, the interface would look close to the same,
but now the --value options are setting fields in the compute special
remote's state:
git-annex addcomputed foo --to ffmpeg-cut
--input source=input.mov
--value starttime=15:00
--value endtime=30:00
The values could be provided to the "git-annex-compute-" program with
environment variables.
"""]]

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doc/todo/compute_special_remote/comment_9_2e10caa2ecbba0f53a3ab031a94c9907._comment
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@ -43,7 +43,8 @@ it depends on. Eg, `git-annex-compute-ffmpeg-cut` could run:
git-annex examinekey --format='${objectpath}' $source
It might be worth formalizing that a given computed key can depend on other
keys, and have git-annex always get/compute those keys first.
keys, and have git-annex always get/compute those keys first. And provide
them to the program in a worktree?
When asked to store a key in the compute special remote, it would verify
that the key can be generated by it. Using the same interface as used to