From patchwork Thu Jan 24 14:13:14 2019
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Subject: [STABLE] partialdiscovery: avoid `undecided` related computation
 sooner than necessary
From: Boris Feld <boris.feld@octobus.net>
X-Patchwork-Id: 37959
Message-Id: <2ac72f1b08d3394c3db2.1548339194@localhost.localdomain>
To: mercurial-devel@mercurial-scm.org
Date: Thu, 24 Jan 2019 09:13:14 -0500

# HG changeset patch
# User Boris Feld <boris.feld@octobus.net>
# Date 1548284862 18000
#      Wed Jan 23 18:07:42 2019 -0500
# Branch stable
# Node ID 2ac72f1b08d3394c3db21c1f576c189118b41eba
# Parent  c953c2a94d68b18c2f3c79262826fdfed743a839
# EXP-Topic discovery-regression
# Available At https://bitbucket.org/octobus/mercurial-devel/
#              hg pull https://bitbucket.org/octobus/mercurial-devel/ -r 2ac72f1b08d3
partialdiscovery: avoid `undecided` related computation sooner than necessary

Changeset 1d30be90c move the update of the `undecided` set within the
`partialdiscovery` object in order to clarify the API.

The update to the `undecided` set was unconditional in 1d30be90c and the first
access to the `self.undecided` property triggered the initial computation of
the set of undecided revisions. As a result, the set was computed much
earlier, at a time where less information is available, immediately followed
by an update of this set to remove common revisions.

To fix this regression, we ignore the `undecided` related logic in
`addcommons` when that `undecided` set has not been computed yet. Code that
actually needs to know the `undecided` set will trigger its computation later.
The change has no effects on semantic because the initial computation
`undecided` set takes all knowns `common` into account.

Example performance running `hg debugdiscovery` from a pypy repo missing 10
changesets:

870a89c6909d: 52.3ms (regression parent)
1d30be90c9dc: 72.0ms (regression)
5a5f504a7175: 64.8ms (this fix parent)
this fix:     52.6ms

diff --git a/mercurial/setdiscovery.py b/mercurial/setdiscovery.py
--- a/mercurial/setdiscovery.py
+++ b/mercurial/setdiscovery.py
@@ -183,7 +183,8 @@ class partialdiscovery(object):
     def addcommons(self, commons):
         """registrer nodes known as common"""
         self._common.addbases(commons)
-        self._common.removeancestorsfrom(self.undecided)
+        if self._undecided is not None:
+            self._common.removeancestorsfrom(self._undecided)
 
     def addmissings(self, missings):
         """registrer some nodes as missing"""