changeset 18275:9818f22785b7

performance: speedup computation of unstable revisions

In their current state, revset calls can be very costly, as we test
predicates on the entire repository.

This change drops revset call in favor of direct testing of the
phase of changesets.

Performance test on my Mercurial checkout
- 19857 total changesets,
- 1584 obsolete changesets,
- 13310 obsolescence markers.

Before:
  ! unstable
  ! wall 0.017366

After this changes:
  ! unstable
  ! wall 0.008093

Performance test on a Mozilla central checkout:
- 117293 total changesets,
- 1 obsolete changeset,
- 1 obsolescence marker.

Before:
  ! unstable
  ! wall 0.045190

After:
  ! unstable
  ! wall 0.000032

--- a/mercurial/obsolete.py	Mon Jan 07 15:50:25 2013 +0100
+++ b/mercurial/obsolete.py	Fri Jan 04 03:15:21 2013 +0100
@@ -660,7 +660,13 @@
 @cachefor('unstable')
 def _computeunstableset(repo):
     """the set of non obsolete revisions with obsolete parents"""
-    return set(repo.revs('(obsolete()::) - obsolete()'))
+    # revset is not efficient enough here
+    # we do (obsolete()::) - obsolete() by hand
+    obs = getrevs(repo, 'obsolete')
+    if not obs:
+        return set()
+    cl = repo.changelog
+    return set(r for r in cl.descendants(obs) if r not in obs)
 
 @cachefor('suspended')
 def _computesuspendedset(repo):