diff -r ffcc649a4e8f -r 445a25bb70be mercurial/repair.py
--- a/mercurial/repair.py	Tue Apr 12 03:40:53 2016 -0700
+++ b/mercurial/repair.py	Tue Apr 12 04:06:50 2016 -0700
@@ -17,6 +17,7 @@
     changegroup,
     error,
     exchange,
+    obsolete,
     util,
 )
 
@@ -313,3 +314,32 @@
                      "ancestors(head() and not bookmark(%s)) - "
                      "ancestors(bookmark() and not bookmark(%s))",
                      mark, mark, mark)
+
+def deleteobsmarkers(obsstore, indices):
+    """Delete some obsmarkers from obsstore and return how many were deleted
+
+    'indices' is a list of ints which are the indices
+    of the markers to be deleted.
+
+    Every invocation of this function completely rewrites the obsstore file,
+    skipping the markers we want to be removed. The new temporary file is
+    created, remaining markers are written there and on .close() this file
+    gets atomically renamed to obsstore, thus guaranteeing consistency."""
+    if not indices:
+        # we don't want to rewrite the obsstore with the same content
+        return
+
+    left = []
+    current = obsstore._all
+    n = 0
+    for i, m in enumerate(current):
+        if i in indices:
+            n += 1
+            continue
+        left.append(m)
+
+    newobsstorefile = obsstore.svfs('obsstore', 'w', atomictemp=True)
+    for bytes in obsolete.encodemarkers(left, True, obsstore._version):
+        newobsstorefile.write(bytes)
+    newobsstorefile.close()
+    return n