This is only implemented for git-annex get so far. It makes git-annex
get nearly twice as fast in a repo with 10k files, all of them present!
But, see the TODO for some caveats.
The catObjectStream' is generic enough to let it be nicely used from
inside Annex monad.
Chan will be faster than DList here. Bearing in mind, it is unbounded,
but in reality will be bounded by the size of the stdio buffer through
git cat-file.
This speeds up --all by about 10% although I think only getting back to
the previous performance before I introduced that DList.
planned to use for an optimisation
most things using stagedDetails were not expecting to get dup files in a
conflicted merge and deal with them, so converted them to use
inRepoDetails.
And convert parser to attoparsec, probably faster.
Before, a parse failure threw the whole --stage output line in to the
filename, which was certianly a bad idea, so fixed that.
Turns out the %(rest) trick was not needed. Instead, just maintain a
list of files we've asked for, and each cat-file response is for the
next file in the list.
This actually benchmarks 25% faster than before! Very surprising, but it
must be due to needing to shove less data through the pipe, and parse
less.
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.
