diff mercurial/pathutil.py @ 33647:377e8ddaebef stable

pathauditor: disable cache of audited paths by default (issue5628)

The initial attempt was to discard cache when appropriate, but it appears
to be error prone. We had to carefully inspect all places where audit() is
called e.g. without actually updating filesystem, before removing files and
directories, etc.

So, this patch disables the cache of audited paths by default, and enables
it only for the following cases:

 - short-lived auditor objects
 - repo.vfs, repo.svfs, and repo.cachevfs, which are managed directories
   and considered sort of append-only (a file/directory would never be
   replaced with a symlink)

There would be more cacheable vfs objects (e.g. mq.queue.opener), but I
decided not to inspect all of them in this patch. We can make them cached
later.

Benchmark result:

- using old clone of http://selenic.com/repo/linux-2.6/ (38319 files)
- on tmpfs
- run HGRCPATH=/dev/null hg up -q --time tip && hg up -q null
- try 4 times and take the last three results

original:
real 7.480 secs (user 1.140+22.760 sys 0.150+1.690)
real 8.010 secs (user 1.070+22.280 sys 0.170+2.120)
real 7.470 secs (user 1.120+22.390 sys 0.120+1.910)

clearcache (the other series):
real 7.680 secs (user 1.120+23.420 sys 0.140+1.970)
real 7.670 secs (user 1.110+23.620 sys 0.130+1.810)
real 7.740 secs (user 1.090+23.510 sys 0.160+1.940)

enable cache only for vfs and svfs (this series):
real 8.730 secs (user 1.500+25.190 sys 0.260+2.260)
real 8.750 secs (user 1.490+25.170 sys 0.250+2.340)
real 9.010 secs (user 1.680+25.340 sys 0.280+2.540)

remove cache function at all (for reference):
real 9.620 secs (user 1.440+27.120 sys 0.250+2.980)
real 9.420 secs (user 1.400+26.940 sys 0.320+3.130)
real 9.760 secs (user 1.530+27.270 sys 0.250+2.970)

--- a/mercurial/pathutil.py	Tue Aug 01 21:03:25 2017 +0900
+++ b/mercurial/pathutil.py	Wed Jul 26 22:10:15 2017 +0900
@@ -33,13 +33,18 @@
     The file system checks are only done when 'realfs' is set to True (the
     default). They should be disable then we are auditing path for operation on
     stored history.
+
+    If 'cached' is set to True, audited paths and sub-directories are cached.
+    Be careful to not keep the cache of unmanaged directories for long because
+    audited paths may be replaced with symlinks.
     '''
 
-    def __init__(self, root, callback=None, realfs=True):
+    def __init__(self, root, callback=None, realfs=True, cached=False):
         self.audited = set()
         self.auditeddir = set()
         self.root = root
         self._realfs = realfs
+        self._cached = cached
         self.callback = callback
         if os.path.lexists(root) and not util.fscasesensitive(root):
             self.normcase = util.normcase
@@ -96,10 +101,11 @@
                 self._checkfs(prefix, path)
             prefixes.append(normprefix)
 
-        self.audited.add(normpath)
-        # only add prefixes to the cache after checking everything: we don't
-        # want to add "foo/bar/baz" before checking if there's a "foo/.hg"
-        self.auditeddir.update(prefixes)
+        if self._cached:
+            self.audited.add(normpath)
+            # only add prefixes to the cache after checking everything: we don't
+            # want to add "foo/bar/baz" before checking if there's a "foo/.hg"
+            self.auditeddir.update(prefixes)
 
     def _checkfs(self, prefix, path):
         """raise exception if a file system backed check fails"""