view tests/test-symlink-placeholder.t @ 24461:05ccfe6763f1

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 <[e-mail]>.

[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.

#require symlink

Create extension that can disable symlink support:

  $ cat > nolink.py <<EOF
  > from mercurial import extensions, util
  > def setflags(orig, f, l, x):
  >     pass
  > def checklink(orig, path):
  >     return False
  > def extsetup(ui):
  >     extensions.wrapfunction(util, 'setflags', setflags)
  >     extensions.wrapfunction(util, 'checklink', checklink)
  > EOF

  $ hg init unix-repo
  $ cd unix-repo
  $ echo foo > a
  $ ln -s a b
  $ hg ci -Am0
  adding a
  adding b
  $ cd ..

Simulate a checkout shared on NFS/Samba:

  $ hg clone -q unix-repo shared
  $ cd shared
  $ rm b
  $ echo foo > b
  $ hg --config extensions.n=$TESTTMP/nolink.py status --debug
  ignoring suspect symlink placeholder "b"

Make a clone using placeholders:

  $ hg --config extensions.n=$TESTTMP/nolink.py clone . ../win-repo
  updating to branch default
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd ../win-repo
  $ cat b
  a (no-eol)
  $ hg --config extensions.n=$TESTTMP/nolink.py st --debug

Empty placeholder:

  $ rm b
  $ touch b
  $ hg --config extensions.n=$TESTTMP/nolink.py st --debug
  ignoring suspect symlink placeholder "b"

Write binary data to the placeholder:

  >>> open('b', 'w').write('this is a binary\0')
  $ hg --config extensions.n=$TESTTMP/nolink.py st --debug
  ignoring suspect symlink placeholder "b"

Write a long string to the placeholder:

  >>> open('b', 'w').write('this' * 1000)
  $ hg --config extensions.n=$TESTTMP/nolink.py st --debug
  ignoring suspect symlink placeholder "b"

Commit shouldn't succeed:

  $ hg --config extensions.n=$TESTTMP/nolink.py ci -m1
  nothing changed
  [1]

Write a valid string to the placeholder:

  >>> open('b', 'w').write('this')
  $ hg --config extensions.n=$TESTTMP/nolink.py st --debug
  M b
  $ hg --config extensions.n=$TESTTMP/nolink.py ci -m1
  $ hg manifest tip --verbose
  644   a
  644 @ b

  $ cd ..