bisect: avoid copying ancestor list for non-merge commits
During a bisection, hg needs to compute a list of all ancestors for every
candidate commit. This is accomplished via a bottom-up traversal of the set of
candidates, during which each revision's ancestor list is populated using the
ancestor list of its parent(s). Previously, this involved copying the entire
list, which could be very long in if the bisection range was large.
To help improve this, we can observe that each candidate commit is visited
exactly once, at which point its ancestor list is copied into its children's
lists and then dropped. In the case of non-merge commits, a commit's ancestor
list consists exactly of its parent's list plus itself. This means that we can
trivially reuse the parent's existing list for one of its non-merge children,
which avoids copying entirely if that commit is the parent's only child. This
makes bisections over linear ranges of commits much faster.
During some informal testing in the large publicly-available `mozilla-central`
repository, this noticeably sped up bisections over large ranges of history:
Setup:
$ cd mozilla-central
$ hg bisect --reset
$ hg bisect --good 0
$ hg log -r tip -T '{rev}\n'
628417
Test:
$ time hg bisect --bad tip --noupdate
Before:
real 3m35.927s
user 3m35.553s
sys 0m0.319s
After:
real 1m41.142s
user 1m40.810s
sys 0m0.285s
# changelog bisection for mercurial
#
# Copyright 2007 Olivia Mackall
# Copyright 2005, 2006 Benoit Boissinot <benoit.boissinot@ens-lyon.org>
#
# Inspired by git bisect, extension skeleton taken from mq.py.
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
import collections
import contextlib
from .i18n import _
from .node import (
hex,
short,
)
from . import error
def bisect(repo, state):
"""find the next node (if any) for testing during a bisect search.
returns a (nodes, number, good) tuple.
'nodes' is the final result of the bisect if 'number' is 0.
Otherwise 'number' indicates the remaining possible candidates for
the search and 'nodes' contains the next bisect target.
'good' is True if bisect is searching for a first good changeset, False
if searching for a first bad one.
"""
repo = repo.unfiltered()
changelog = repo.changelog
clparents = changelog.parentrevs
skip = {changelog.rev(n) for n in state[b'skip']}
def buildancestors(bad, good):
badrev = min([changelog.rev(n) for n in bad])
ancestors = collections.defaultdict(lambda: None)
for rev in repo.revs(b"(%ln::%d) - (::%ln)", good, badrev, good):
ancestors[rev] = []
if ancestors[badrev] is None:
return badrev, None
return badrev, ancestors
good = False
badrev, ancestors = buildancestors(state[b'bad'], state[b'good'])
if not ancestors: # looking for bad to good transition?
good = True
badrev, ancestors = buildancestors(state[b'good'], state[b'bad'])
bad = changelog.node(badrev)
if not ancestors: # now we're confused
if (
len(state[b'bad']) == 1
and len(state[b'good']) == 1
and state[b'bad'] != state[b'good']
):
raise error.Abort(_(b"starting revisions are not directly related"))
raise error.Abort(
_(b"inconsistent state, %d:%s is good and bad")
% (badrev, short(bad))
)
# build children dict
children = {}
visit = collections.deque([badrev])
candidates = []
while visit:
rev = visit.popleft()
if ancestors[rev] == []:
candidates.append(rev)
for prev in clparents(rev):
if prev != -1:
if prev in children:
children[prev].append(rev)
else:
children[prev] = [rev]
visit.append(prev)
candidates.sort()
# have we narrowed it down to one entry?
# or have all other possible candidates besides 'bad' have been skipped?
tot = len(candidates)
unskipped = [c for c in candidates if (c not in skip) and (c != badrev)]
if tot == 1 or not unskipped:
return ([changelog.node(c) for c in candidates], 0, good)
perfect = tot // 2
# find the best node to test
best_rev = None
best_len = -1
poison = set()
for rev in candidates:
if rev in poison:
# poison children
poison.update(children.get(rev, []))
continue
a = ancestors[rev] or [rev]
ancestors[rev] = None
x = len(a) # number of ancestors
y = tot - x # number of non-ancestors
value = min(x, y) # how good is this test?
if value > best_len and rev not in skip:
best_len = value
best_rev = rev
if value == perfect: # found a perfect candidate? quit early
break
if y < perfect and rev not in skip: # all downhill from here?
# poison children
poison.update(children.get(rev, []))
continue
unvisited = []
for c in children.get(rev, []):
if ancestors[c]:
ancestors[c] = list(set(ancestors[c] + a))
else:
unvisited.append(c)
# Reuse existing ancestor list for the first unvisited child to avoid
# excessive copying for linear portions of history.
if unvisited:
first = unvisited.pop(0)
for c in unvisited:
ancestors[c] = a + [c]
a.append(first)
ancestors[first] = a
assert best_rev is not None
best_node = changelog.node(best_rev)
return ([best_node], tot, good)
def extendrange(repo, state, nodes, good):
# bisect is incomplete when it ends on a merge node and
# one of the parent was not checked.
parents = repo[nodes[0]].parents()
if len(parents) > 1:
if good:
side = state[b'bad']
else:
side = state[b'good']
num = len({i.node() for i in parents} & set(side))
if num == 1:
return parents[0].ancestor(parents[1])
return None
def load_state(repo):
state = {b'current': [], b'good': [], b'bad': [], b'skip': []}
for l in repo.vfs.tryreadlines(b"bisect.state"):
kind, node = l[:-1].split()
node = repo.unfiltered().lookup(node)
if kind not in state:
raise error.Abort(_(b"unknown bisect kind %s") % kind)
state[kind].append(node)
return state
def save_state(repo, state):
f = repo.vfs(b"bisect.state", b"w", atomictemp=True)
with repo.wlock():
for kind in sorted(state):
for node in state[kind]:
f.write(b"%s %s\n" % (kind, hex(node)))
f.close()
def resetstate(repo):
"""remove any bisect state from the repository"""
if repo.vfs.exists(b"bisect.state"):
repo.vfs.unlink(b"bisect.state")
def checkstate(state):
"""check we have both 'good' and 'bad' to define a range
Raise StateError exception otherwise."""
if state[b'good'] and state[b'bad']:
return True
if not state[b'good']:
raise error.StateError(_(b'cannot bisect (no known good revisions)'))
else:
raise error.StateError(_(b'cannot bisect (no known bad revisions)'))
@contextlib.contextmanager
def restore_state(repo, state, node):
try:
yield
finally:
state[b'current'] = [node]
save_state(repo, state)
def get(repo, status):
"""
Return a list of revision(s) that match the given status:
- ``good``, ``bad``, ``skip``: csets explicitly marked as good/bad/skip
- ``goods``, ``bads`` : csets topologically good/bad
- ``range`` : csets taking part in the bisection
- ``pruned`` : csets that are goods, bads or skipped
- ``untested`` : csets whose fate is yet unknown
- ``ignored`` : csets ignored due to DAG topology
- ``current`` : the cset currently being bisected
"""
state = load_state(repo)
if status in (b'good', b'bad', b'skip', b'current'):
return map(repo.unfiltered().changelog.rev, state[status])
else:
# In the following sets, we do *not* call 'bisect()' with more
# than one level of recursion, because that can be very, very
# time consuming. Instead, we always develop the expression as
# much as possible.
# 'range' is all csets that make the bisection:
# - have a good ancestor and a bad descendant, or conversely
# that's because the bisection can go either way
range = b'( bisect(bad)::bisect(good) | bisect(good)::bisect(bad) )'
_t = repo.revs(b'bisect(good)::bisect(bad)')
# The sets of topologically good or bad csets
if len(_t) == 0:
# Goods are topologically after bads
goods = b'bisect(good)::' # Pruned good csets
bads = b'::bisect(bad)' # Pruned bad csets
else:
# Goods are topologically before bads
goods = b'::bisect(good)' # Pruned good csets
bads = b'bisect(bad)::' # Pruned bad csets
# 'pruned' is all csets whose fate is already known: good, bad, skip
skips = b'bisect(skip)' # Pruned skipped csets
pruned = b'( (%s) | (%s) | (%s) )' % (goods, bads, skips)
# 'untested' is all cset that are- in 'range', but not in 'pruned'
untested = b'( (%s) - (%s) )' % (range, pruned)
# 'ignored' is all csets that were not used during the bisection
# due to DAG topology, but may however have had an impact.
# E.g., a branch merged between bads and goods, but whose branch-
# point is out-side of the range.
iba = b'::bisect(bad) - ::bisect(good)' # Ignored bads' ancestors
iga = b'::bisect(good) - ::bisect(bad)' # Ignored goods' ancestors
ignored = b'( ( (%s) | (%s) ) - (%s) )' % (iba, iga, range)
if status == b'range':
return repo.revs(range)
elif status == b'pruned':
return repo.revs(pruned)
elif status == b'untested':
return repo.revs(untested)
elif status == b'ignored':
return repo.revs(ignored)
elif status == b"goods":
return repo.revs(goods)
elif status == b"bads":
return repo.revs(bads)
else:
raise error.ParseError(_(b'invalid bisect state'))
def label(repo, node):
rev = repo.changelog.rev(node)
# Try explicit sets
if rev in get(repo, b'good'):
# i18n: bisect changeset status
return _(b'good')
if rev in get(repo, b'bad'):
# i18n: bisect changeset status
return _(b'bad')
if rev in get(repo, b'skip'):
# i18n: bisect changeset status
return _(b'skipped')
if rev in get(repo, b'untested') or rev in get(repo, b'current'):
# i18n: bisect changeset status
return _(b'untested')
if rev in get(repo, b'ignored'):
# i18n: bisect changeset status
return _(b'ignored')
# Try implicit sets
if rev in get(repo, b'goods'):
# i18n: bisect changeset status
return _(b'good (implicit)')
if rev in get(repo, b'bads'):
# i18n: bisect changeset status
return _(b'bad (implicit)')
return None
def printresult(ui, repo, state, displayer, nodes, good):
repo = repo.unfiltered()
if len(nodes) == 1:
# narrowed it down to a single revision
if good:
ui.write(_(b"The first good revision is:\n"))
else:
ui.write(_(b"The first bad revision is:\n"))
displayer.show(repo[nodes[0]])
extendnode = extendrange(repo, state, nodes, good)
if extendnode is not None:
ui.write(
_(
b'Not all ancestors of this changeset have been'
b' checked.\nUse bisect --extend to continue the '
b'bisection from\nthe common ancestor, %s.\n'
)
% extendnode
)
else:
# multiple possible revisions
if good:
ui.write(
_(
b"Due to skipped revisions, the first "
b"good revision could be any of:\n"
)
)
else:
ui.write(
_(
b"Due to skipped revisions, the first "
b"bad revision could be any of:\n"
)
)
for n in nodes:
displayer.show(repo[n])
displayer.close()