Note that this fix only solves the statistics problem, if
all duplicates are marked for repacking.
If not all duplicates are marked for repacking, we lack the
information which
The situation that not all duplicates are marked for repacking can occur
when using the `max-repack-size` option
Add a callback to the PruneOptions struct which calculates the number of
bytes allowed to be unused after prune is done. This way, the logic is
closer to the option parsing code.
Also, add an explicit option `unlimited` for the use case when storage
does not matter but bandwidth and time do. Internally, this sets the
maximum number of unused bytes to MaxUint64.
Rework the documentation slightly so that no more "packs" are
mentioned and it talks about "files" instead.
Make it clear in the documentation that the percentage given to
`--max-unused` is relative to the whole repository size after pruning is
done. If specified, it must be below 100%, otherwise the repository
would contain 100% of unused data, which is pointless.
I had a hard time coming up with the correct formula to calculate the
maximum number of unused bytes based on the number of used bytes. For a
fraction `p` (0 ≤ p < 1), a repo with `u` bytes used, and the number of
unused bytes `x` the following holds:
x ≤ p * (u+x)
⇔ x ≤ p*u + p*x
⇔ x - p*x ≤ p*u
⇔ x * (1-p) ≤ p*u
⇔ x ≤ p/(1-p) * u
The previous check only approximately verified whether all required
blobs were found. However, after forgetting a few snapshots the
repository contains lots of unused blobs whose number can be sufficient
to make up for missing packs.
When coupled with a malfunctioning backend that temporarily returns broken
data this could cause restic to regard the corresponding packs as
invalid and thereby delete data that's still in use. This change lets
restic play it safe and refuse to delete anything if data is missing.
The seen BlobSet always contained a subset of the entries in blobs.
Thus use blobs instead and avoid the memory overhead of the second set.
Suggested-by: Alexander Weiss <alex@weissfam.de>
