This can reduce the size of the branch by up to 8%. My test was
running git-annex add 1000 times on one file each.
Lots of different high-resolution timestamps were recorded before
and eliminating those, after packing, the git repo was 8% smaller.
Due to the use of vector clocks, high resolution timestamps are
not necessary to make clear which information is most recent when
eg, a value is changed repeatedly in the same second. In such a
case, the vector clock will be advanced to the next second after
the last modification. For example, running
git-annex numcopies 1; git-annex numcopies 2
The first will record the current second, while the next records
the second after that even if it runs in the same second.
As for conflicting information written to two different clones of the
repository, this will make git-annex sometimes pick information that
was written earlier in a second over information written later in the
same second. Usually git-annex does not write conflicting information,
but there are some cases where it could. Eg, storing an object on a remote
can update the remote state log with some state. If two repos both store the
same object, and end up storing different remote state for some reason,
this can result in one that ran a tiny bit later winning. Such a situation
seems unlikely to be user visible. And a small amount of clock skew could
already result in such things.
The only case I can think of where this might be a user visible change
is if a configuration command like git-annex numcopies is being run
in 2 clones of a repository on the same machine at very
close to the same time. Then the user will know which they ran last,
and git-annex won't.
If that did become a problem, this could be dialed back to eg log
milliseconds with still some space saving.
Drop support for building with ghc older than 8.4.4, and with older
versions of serveral haskell libraries than will be included in Debian 10.
The only remaining version ifdefs in the entire code base are now a couple
for aws!
This commit should only be merged after the Debian 10 release.
And perhaps it will need to wait longer than that; it would make
backporting new versions of git-annex to Debian 9 (stretch) which
has been actively happening as recently as this year.
This commit was sponsored by Ilya Shlyakhter.
This is not as efficient as using ByteStrings throughout, but converting
the String to ByteString is actually significantly faster than the old
parser.
benchmarking parse/old
time 9.657 μs (9.600 μs .. 9.732 μs)
1.000 R² (0.999 R² .. 1.000 R²)
mean 9.703 μs (9.645 μs .. 9.785 μs)
std dev 231.6 ns (161.5 ns .. 323.7 ns)
variance introduced by outliers: 25% (moderately inflated)
benchmarking parse/new
time 834.6 ns (797.1 ns .. 886.9 ns)
0.987 R² (0.976 R² .. 0.999 R²)
mean 816.4 ns (802.7 ns .. 845.1 ns)
std dev 62.39 ns (37.66 ns .. 108.4 ns)
variance introduced by outliers: 82% (severely inflated)
There is a small behavior change from the old parsePOSIXTime,
which accepted any amount of trailing whitespace after the timestamp.
That behavior was not documented, and it doesn't seem anything relied on it.
Luckily, this did not affect any git-annex log files, since they all
include the trailing 's' for backwards compatability reasons.
But, if I later want to drop that, this is the first commit where
git-annex can be trusted to parse that right.
The misparse caused it to be off by up to 10 seconds.
