diff mercurial/changegroup.py @ 40432:968dd7e02ac5

changegroup: allow to force delta to be against p1

This new developer option is useful to general more "generic" bundle. Without
this option, a bundle generated from the repository use deltas similar to the
one stored in the specific repository it was generated from. This makes
performance testing a bit tricky.

Using deltas similar to the final result means all delta stored in the bundle
can be applied to the target repository without any further processing (except
for the rare case of a full snapshot). The application of such bundles
(almost) never exercises the (slower) path of searching for a new valid delta.
This result in unrealistic and too favorable timing and profile.

Instead, we introduce an option to make sure all revisions are stored as a
delta against p1. It might not be the best generation option, but it
guarantees that the content will be "generic", not favoring a specific target.

--- a/mercurial/changegroup.py	Tue Oct 09 23:26:35 2018 +0200
+++ b/mercurial/changegroup.py	Wed Oct 10 00:21:02 2018 +0200
@@ -697,9 +697,16 @@
         progress = repo.ui.makeprogress(topic, unit=_('chunks'),
                                         total=len(nodes))
 
+    configtarget = repo.ui.config('devel', 'bundle.delta')
+    if configtarget not in ('', 'p1'):
+        msg = _("""config "devel.bundle.delta" as unknown value: %s""")
+        repo.ui.warn(msg % configtarget)
+
     deltamode = repository.CG_DELTAMODE_STD
     if forcedeltaparentprev:
         deltamode = repository.CG_DELTAMODE_PREV
+    elif configtarget == 'p1':
+        deltamode = repository.CG_DELTAMODE_P1
 
     revisions = store.emitrevisions(
         nodes,