My worry was that a preferred content expression that matches on metadata
would have removed the location log from cache, causing an expensive
re-read when a Seek action later checked the location log.
Especially when the --all optimisation in the previous commit
pre-cached the location log.
This also means that the --all optimisation could cache the metadata log
too, if it wanted too, but not currently done.
The cache is a list, with the most recently accessed file first. That
optimises it for the common case of reading the same file twice, eg a
get, examine, followed by set reads it twice. And sync --content reads the
location log 3 times in a row commonly.
But, as a list, it should not be made to be too long. I thought about
expanding it to 5 items, but that seemed unlikely to be a win commonly
enough to outweigh the extra time spent checking the cache.
Clearly there could be some further benchmarking and tuning here.
This assumes that no location log files will have a newline or carriage
return in their name. catObjectStream skips any such files due to
cat-file not supporting them.
Keys have been prevented from containing newlines since 2011,
commit 480495beb4. If some old repo
had a key with a newline in it, --all will just skip processing that key.
Other things, like .git/annex/unused files certianly assume no newlines in
keys too, and AFAICR, such keys never actually worked.
Carriage return is escaped by preSanitizeKeyName since 2013. WORM keys
generated before that point could perhaps contain a CR. (URL probably not,
http probably doesn't support an URL with a raw CR in it.) So, added
a warning in fsck about such keys. Although, fsck --all will naturally
skip them, so won't be able to warn about them. Not entirely
satisfactory, but I'll bet there are not really any such keys in
existence.
Thanks to Lukey for finding this optimisation.
The cache was removed way back in 2012,
commit 3417c55189
Then I forgot I had removed it! I remember clearly multiple times when I
thought, "this reads the same data twice, but the cache will avoid that
being very expensive".
The reason it was removed was it messed up the assistant noticing when
other processes made changes. That same kind of problem has recently
been addressed when adding the optimisation to avoid reading the journal
unnecessarily.
Indeed, enableInteractiveJournalAccess is run in just the
right places, so can just piggyback on it to know when it's not safe
to use the cache.
adb shell has sha256sum sha1sum and some others, so they could be used.
They're provided by toybox, so seem about as likely to keep
working as find and stat, which it already depends on.
Or to not add a dep, could use stat the same as getExportContentIdentifier
to get a mtime, and make a WORM key. But do I really want this to
default to WORM?
Unsure what's the best path, so punting for now.
Only supported by some special remotes: directory
I need to check the rest and they're currently missing methods until I do.
git-annex sync --no-content does not yet use this to do imports
