branchcache: lazily validate nodes from the branchmap

On my personal hg-repository with 365 entries in .hg/cache/branch2, following
are the numbers for perfbranchmapload.

Before this patch:

! wall 0.000866 comb 0.000000 user 0.000000 sys 0.000000 (best of 2680)
! wall 0.001525 comb 0.000000 user 0.000000 sys 0.000000 (max of 2680)
! wall 0.001107 comb 0.001097 user 0.001086 sys 0.000011 (avg of 2680)
! wall 0.001104 comb 0.000000 user 0.000000 sys 0.000000 (median of 2680)

With this patch:

! wall 0.000530 comb 0.000000 user 0.000000 sys 0.000000 (best of 4240)
! wall 0.001078 comb 0.000000 user 0.000000 sys 0.000000 (max of 4240)
! wall 0.000696 comb 0.000693 user 0.000677 sys 0.000017 (avg of 4240)
! wall 0.000690 comb 0.000000 user 0.000000 sys 0.000000 (median of 4240)

On our internal repository with ~20k entries in branchcache, I see improvement
from 0.125 sec to 0.066 sec which is 47% speed up.

The above are the numbers of perfbranchmapload which shows how much time we
saved by not validating the nodes. But we need to validate some nodes. Following
are timings of some mercurial operations which have speed up because of this
lazy validation of nodes:

No-op `hg update` on our internal repository (Avg on 4 runs):

Before: 0.540 secs
After: 0.430 secs

Setting a branch name which already exists without --force (Avg of 4 runs):

Before: 0.510 secs
After: 0.250 secs

I ran the ASV performance suite and was unable to see any improvements except
there was improvement of perfdirstatewrite() on netbeans which I think was not
related.

I looked into the commit code, the command which I am trying to speedup, it
looks like it uses revbranchcache to update the branchcache.

Differential Revision: https://phab.mercurial-scm.org/D6208

mercurial/branchmap.py

@@ -210,16 +210,20 b' class branchcache(object):'
         self._entries[key] = value
 
     def __getitem__(self, key):
+        self._verifybranch(key)
         return self._entries[key]
 
     def __contains__(self, key):
+        self._verifybranch(key)
         return key in self._entries
 
     def iteritems(self):
+        self._verifyall()
         return self._entries.iteritems()
 
     def hasbranch(self, label):
         """ checks whether a branch of this name exists or not """
+        self._verifybranch(label)
         return label in self._entries
 
     @classmethod
@@ -262,7 +266,6 b' class branchcache(object):'
     def load(self, repo, lineiter):
         """ fully loads the branchcache by reading from the file using the line
         iterator passed"""
-        cl = repo.changelog
         for line in lineiter:
             line = line.rstrip('\n')
             if not line:
@@ -272,14 +275,9 b' class branchcache(object):'
                 raise ValueError(r'invalid branch state')
             label = encoding.tolocal(label.strip())
             node = bin(node)
-            if not cl.hasnode(node):
-                raise ValueError(
-                    r'node %s does not exist' % pycompat.sysstr(hex(node)))
             self._entries.setdefault(label, []).append(node)
-            self._verifiedbranches.add(label)
             if state == 'c':
                 self._closednodes.add(node)
-        self._closedverified = True
 
     @staticmethod
     def _filename(repo):
@@ -306,6 +304,7 b' class branchcache(object):'
         otherwise return last closed head and true.'''
         tip = heads[-1]
         closed = True
+        self._verifyclosed()
         for h in reversed(heads):
             if h not in self._closednodes:
                 tip = h
@@ -320,9 +319,11 b' class branchcache(object):'
         return self._branchtip(self[branch])[0]
 
     def iteropen(self, nodes):
+        self._verifyclosed()
         return (n for n in nodes if n not in self._closednodes)
 
     def branchheads(self, branch, closed=False):
+        self._verifybranch(branch)
         heads = self._entries[branch]
         if not closed:
             heads = list(self.iteropen(heads))
@@ -334,10 +335,12 b' class branchcache(object):'
 
     def iterheads(self):
         """ returns all the heads """
+        self._verifyall()
         return self._entries.itervalues()
 
     def copy(self):
         """return an deep copy of the branchcache object"""
+        self._verifyall()
         return type(self)(
             self._entries, self.tipnode, self.tiprev, self.filteredhash,
             self._closednodes)