# HG changeset patch
# User Sune Foldager <cryo@cyanite.org>
# Date 1305206673 -7200
# Node ID f94993769c87cd1c56509560fc213cd1da406b44
# Parent  1b8e421d8e424d2c910689f9c19a5fe738ce7be4
revlog: improve delta generation heuristics for generaldelta

Without this change, pulls (and clones) into a generaldelta repository could
generate very inefficient revlogs, the size of which could be at least twice
the original size.

This was caused by the generated delta chains covering too large distances,
causing new chains to be built far too often. This change addresses the
problem by forcing a delta against second parent or against the previous
revision, when the first parent delta is in danger of creating a long chain.

diff -r 1b8e421d8e42 -r f94993769c87 mercurial/revlog.py
--- a/mercurial/revlog.py	Thu May 12 14:31:07 2011 +0200
+++ b/mercurial/revlog.py	Thu May 12 15:24:33 2011 +0200
@@ -1033,7 +1033,12 @@
         # should we try to build a delta?
         if prev != nullrev:
             if self._generaldelta:
-                d = builddelta(p1r)
+                if p1r >= basecache[1]:
+                    d = builddelta(p1r)
+                elif p2r >= basecache[1]:
+                    d = builddelta(p2r)
+                else:
+                    d = builddelta(prev)
             else:
                 d = builddelta(prev)
             dist, l, data, base, chainbase = d