diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -235,8 +235,7 @@ class localrepository(object):
         if os.path.exists(self.join("journal")):
             self.ui.status(_("rolling back interrupted transaction\n"))
             transaction.rollback(self.opener, self.join("journal"))
-            self.manifest = manifest.manifest(self.opener)
-            self.changelog = changelog.changelog(self.opener)
+            self.reload()
             return True
         else:
             self.ui.warn(_("no interrupted transaction available\n"))
@@ -250,10 +249,20 @@ class localrepository(object):
             self.ui.status(_("rolling back last transaction\n"))
             transaction.rollback(self.opener, self.join("undo"))
             util.rename(self.join("undo.dirstate"), self.join("dirstate"))
-            self.dirstate.read()
+            self.reload()
+            self.wreload()
         else:
             self.ui.warn(_("no undo information available\n"))
 
+    def wreload(self):
+        self.dirstate.read()
+
+    def reload(self):
+        self.changelog.load()
+        self.manifest.load()
+        self.tagscache = None
+        self.nodetagscache = None
+
     def do_lock(self, lockname, wait, releasefn=None, acquirefn=None):
         try:
             l = lock.lock(self.join(lockname), 0, releasefn)
@@ -267,12 +276,12 @@ class localrepository(object):
         return l
 
     def lock(self, wait=1):
-        return self.do_lock("lock", wait)
+        return self.do_lock("lock", wait, acquirefn=self.reload)
 
     def wlock(self, wait=1):
         return self.do_lock("wlock", wait,
                             self.dirstate.write,
-                            self.dirstate.read)
+                            self.wreload)
 
     def checkfilemerge(self, filename, text, filelog, manifest1, manifest2):
         "determine whether a new filenode is needed"
diff --git a/mercurial/revlog.py b/mercurial/revlog.py
--- a/mercurial/revlog.py
+++ b/mercurial/revlog.py
@@ -13,7 +13,7 @@ of the GNU General Public License, incor
 from node import *
 from i18n import gettext as _
 from demandload import demandload
-demandload(globals(), "binascii errno heapq mdiff sha struct zlib")
+demandload(globals(), "binascii errno heapq mdiff os sha struct zlib")
 
 def hash(text, p1, p2):
     """generate a hash from the given text and its parent hashes
@@ -187,15 +187,33 @@ class revlog(object):
         self.indexfile = indexfile
         self.datafile = datafile
         self.opener = opener
+
+        self.indexstat = None
         self.cache = None
         self.chunkcache = None
+        self.load()
 
+    def load(self):
         try:
-            i = self.opener(self.indexfile).read()
+            f = self.opener(self.indexfile)
         except IOError, inst:
             if inst.errno != errno.ENOENT:
                 raise
             i = ""
+        else:
+            try:
+                st = os.fstat(f.fileno())
+            except AttributeError, inst:
+                st = None
+            else:
+                oldst = self.indexstat
+                if (oldst and st.st_dev == oldst.st_dev
+                    and st.st_ino == oldst.st_ino
+                    and st.st_mtime == oldst.st_mtime
+                    and st.st_ctime == oldst.st_ctime):
+                    return
+            self.indexstat = st
+            i = f.read()
 
         if i and i[:4] != "\0\0\0\0":
             raise RevlogError(_("incompatible revlog signature on %s") %