changeset 38513:6db38c9d7e00

revlog: efficient implementation of 'descendant' Iterating over descendants is costly, because there are no "parent -> children" pointers. Walking the other way around is much more efficient, especially on large repositories, where descendant walks can cost seconds. And the other hand, common ancestors code follows links in the right direction and has a compiled implementation. In real life usage, this saved up to 80s during some pull operations, where descendant test happens in extension code.
author Boris Feld <boris.feld@octobus.net>
date Fri, 22 Jun 2018 00:05:20 +0100
parents 99f864b34451
children cc3543c87de5
files mercurial/revlog.py
diffstat 1 files changed, 4 insertions(+), 6 deletions(-) [+]
line wrap: on
line diff
--- a/mercurial/revlog.py	Thu Jun 21 23:56:51 2018 +0100
+++ b/mercurial/revlog.py	Fri Jun 22 00:05:20 2018 +0100
@@ -1376,16 +1376,14 @@
         return c
 
     def descendant(self, start, end):
+        """True if revision 'end' is an descendant of revision 'start'
+
+        A revision is considered as a descendant of itself."""
         if start == nullrev:
             return True
         elif start == end:
             return True
-        for i in self.descendants([start]):
-            if i == end:
-                return True
-            elif i > end:
-                break
-        return False
+        return start in self._commonancestorsheads(start, end)
 
     def commonancestorsheads(self, a, b):
         """calculate all the heads of the common ancestors of nodes a and b"""