When using git annex unlock, followed by git annex add, it currently checksums files, even if the file has not changed.
Direct mode has a better approach for this: The inode cache can pretty
reliably detect if a file has been modified. So,
unlock could note
a file's inode cache info, and then
add could check if a file's inode
cache is unchanged, and rather than re-checksum it, just perform a fast
Question: How would
add know what key's inode cache to look at? Seems it
would need to either check the git branch (as direct mode does, but this is
rather slow and would slow down
add in the more common case of adding
lots of new files), or use a yet-unimplemented caching database.
Or, the inode cache could be stored in a map with the work tree filename,
but that diverges from how direct mode uses inode caches.
Observation: Using the inode cache info to detect changes is not perfect; if a file is modified without changing its size or mtime, the inode cache won't be able to tell it's changed. This is unlikely, but possible. In direct mode, the worst that can happen in this case is probably that a modified file doesn't get added and committed. But, using the inode cache for unlocked files would result in any such modified versions being thrown away when the file is added, which is much more data lossy..
This bug was regarding v5 unlock/lock. In v6 mode, locking a file doesn't need to rechecksum it; the key is pulled out of the associated files database, and the inode cache is used to detect if the unlocked file has been modified and so avoid data loss.
So, this is done but only for v6 mode. I don't think I want to backport it to v5 mode though; it fell out naturally as a consequence of v6 mode, but to support it in v5 mode would be a lot more work. --Joey