osutil: use getdirentriesattr on OS X if possible
This is a significant win for large repositories on OS X, especially with a
cold cache. Unfortunately we need to keep the lstat-based implementation around
for two reasons:
- Not all filesystems support this call.
- There's an edge case in which it's best to fall back to avoid a retry loop.
More about this in the comments.
The below tests are all performed on a Mac with an SSD running OS X 10.9, on a
repository with over 200k files. The results are best of 5 with simulated
best-effort conditions.
The gains with a hot cache are pretty impressive: 'hg status' goes from 5.18
seconds to 3.79 seconds.
However, a repository that large will probably already be using something like
hgwatchman [1], which helps much more (for this repo, 'hg status' with
hgwatchman is approximately 1 second). Where this really helps is when the
cache is cold [2]: hg status goes from 31.0 seconds to 9.66.
See http://lists.apple.com/archives/filesystem-dev/2014/Dec/msg00002.html for
some more discussion about this function.
This is based on a patch by Sean Farley <sean@farley.io>.
[1] https://bitbucket.org/facebook/hgwatchman
[2] There appears to be no easy way to clear the file cache (aka "vnodes") on
OS X short of rebooting. purge(8) purportedly does that but in my testing had
little effect. The workaround I came up with was to assume that vnode eviction
was LRU, make sure the kern.maxvnodes sysctl is smaller than the size of the
repository, then make sure we'd always miss the cache by running 'hg status' in
another clone of the repository before running it in the test repository.
Mercurial
=========
Mercurial is a fast, easy to use, distributed revision control tool
for software developers.
Basic install:
$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
Running without installing:
$ make local # build for inplace usage
$ ./hg --version # should show the latest version
See http://mercurial.selenic.com/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.