setdiscovery: add a discovery.grow-sample.dynamic option

The current discovery dynamically adapt to complex situations. This
makes it quick and effective, but also harder so study the effects of
other improvements in such complex situation.

So we add a new option to control this too.

Differential Revision: https://phab.mercurial-scm.org/D10233

mercurial/configitems.py

@@ -737,6 +737,14 b' coreconfigitem('
     b'discovery.grow-sample',
     default=True,
 )
+# When discovery.grow-sample.dynamic is True, the default, the sample size is
+# adapted to the shape of the undecided set (it is set to the max of:
+# <target-size>, len(roots(undecided)), len(heads(undecided)
+coreconfigitem(
+    b'devel',
+    b'discovery.grow-sample.dynamic',
+    default=True,
+)
 # discovery.grow-sample.rate control the rate at which the sample grow
 coreconfigitem(
     b'devel',

mercurial/debugcommands.py

@@ -1024,6 +1024,12 b' def debugdiscovery(ui, repo, remoteurl=b'
       If False, the sample size used in set discovery will not be increased
       through the process
 
+    * devel.discovery.grow-sample.dynamic=True
+
+      When discovery.grow-sample.dynamic is True, the default, the sample size is
+      adapted to the shape of the undecided set (it is set to the max of:
+      <target-size>, len(roots(undecided)), len(heads(undecided)
+
     * devel.discovery.grow-sample.rate=1.05
 
       the rate at which the sample grow

mercurial/setdiscovery.py

@@ -429,12 +429,16 b' def findcommonheads('
     # full blown discovery
 
     # if the server has a limit to its arguments size, we can't grow the sample.
-    grow_sample = local.ui.configbool(b'devel', b'discovery.grow-sample')
+    configbool = local.ui.configbool
+    grow_sample = configbool(b'devel', b'discovery.grow-sample')
     grow_sample = grow_sample and not remote.limitedarguments
 
+    dynamic_sample = configbool(b'devel', b'discovery.grow-sample.dynamic')
+    hard_limit_sample = not (dynamic_sample or remote.limitedarguments)
+
     randomize = ui.configbool(b'devel', b'discovery.randomize')
     disco = partialdiscovery(
-        local, ownheads, not grow_sample, randomize=randomize
+        local, ownheads, hard_limit_sample, randomize=randomize
     )
     if initial_head_exchange:
         # treat remote heads (and maybe own heads) as a first implicit sample