sparse-read: move from a recursive-based approach to a heap-based one
The previous recursive approach was trying to optimise each read slice to have
a good density. It had the tendency to over-optimize smaller slices while
leaving larger hole in others.
The new approach focuses on improving the combined density of all the reads,
instead of the individual slices. It slices at the largest gaps first, as they
reduce the total amount of read data the most efficiently.
Another benefit of this approach is that we iterate over the delta chain only
once, reducing the overhead of slicing long delta chains.
On the repository we use for tests, the new approach shows similar or faster
performance than the current default linear full read.
The repository contains about 450,000 revisions with many concurrent
topological branches. Tests have been run on two versions of the repository:
one built with the current delta constraint, and the other with an unlimited
delta span (using 'experimental.maxdeltachainspan=0')
Below are timings for building 1% of all the revision in the manifest log using
'hg perfrevlogrevisions -m'. Times are given in seconds. They include the new
couple of follow-up changeset in this series.
delta-span standard unlimited
linear-read 922s 632s
sparse-read 814s 566s
# changelog bisection for mercurial
#
# Copyright 2007 Matt 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.
from __future__ import absolute_import
import collections
from .i18n import _
from .node import (
hex,
short,
)
from . import (
error,
)
def bisect(changelog, 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.
"""
clparents = changelog.parentrevs
skip = set([changelog.rev(n) for n in state['skip']])
def buildancestors(bad, good):
# only the earliest bad revision matters
badrev = min([changelog.rev(n) for n in bad])
goodrevs = [changelog.rev(n) for n in good]
goodrev = min(goodrevs)
# build visit array
ancestors = [None] * (len(changelog) + 1) # an extra for [-1]
# set nodes descended from goodrevs
for rev in goodrevs:
ancestors[rev] = []
for rev in changelog.revs(goodrev + 1):
for prev in clparents(rev):
if ancestors[prev] == []:
ancestors[rev] = []
# clear good revs from array
for rev in goodrevs:
ancestors[rev] = None
for rev in changelog.revs(len(changelog), goodrev):
if ancestors[rev] is None:
for prev in clparents(rev):
ancestors[prev] = None
if ancestors[badrev] is None:
return badrev, None
return badrev, ancestors
good = False
badrev, ancestors = buildancestors(state['bad'], state['good'])
if not ancestors: # looking for bad to good transition?
good = True
badrev, ancestors = buildancestors(state['good'], state['bad'])
bad = changelog.node(badrev)
if not ancestors: # now we're confused
if (len(state['bad']) == 1 and len(state['good']) == 1 and
state['bad'] != state['good']):
raise error.Abort(_("starting revisions are not directly related"))
raise error.Abort(_("inconsistent state, %s:%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
for c in children.get(rev, []):
if ancestors[c]:
ancestors[c] = list(set(ancestors[c] + a))
else:
ancestors[c] = a + [c]
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['bad']
else:
side = state['good']
num = len(set(i.node() for i in parents) & set(side))
if num == 1:
return parents[0].ancestor(parents[1])
return None
def load_state(repo):
state = {'current': [], 'good': [], 'bad': [], 'skip': []}
for l in repo.vfs.tryreadlines("bisect.state"):
kind, node = l[:-1].split()
node = repo.lookup(node)
if kind not in state:
raise error.Abort(_("unknown bisect kind %s") % kind)
state[kind].append(node)
return state
def save_state(repo, state):
f = repo.vfs("bisect.state", "w", atomictemp=True)
with repo.wlock():
for kind in sorted(state):
for node in state[kind]:
f.write("%s %s\n" % (kind, hex(node)))
f.close()
def resetstate(repo):
"""remove any bisect state from the repository"""
if repo.vfs.exists("bisect.state"):
repo.vfs.unlink("bisect.state")
def checkstate(state):
"""check we have both 'good' and 'bad' to define a range
Raise Abort exception otherwise."""
if state['good'] and state['bad']:
return True
if not state['good']:
raise error.Abort(_('cannot bisect (no known good revisions)'))
else:
raise error.Abort(_('cannot bisect (no known bad revisions)'))
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 ('good', 'bad', 'skip', 'current'):
return map(repo.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 = '( bisect(bad)::bisect(good) | bisect(good)::bisect(bad) )'
_t = repo.revs('bisect(good)::bisect(bad)')
# The sets of topologically good or bad csets
if len(_t) == 0:
# Goods are topologically after bads
goods = 'bisect(good)::' # Pruned good csets
bads = '::bisect(bad)' # Pruned bad csets
else:
# Goods are topologically before bads
goods = '::bisect(good)' # Pruned good csets
bads = 'bisect(bad)::' # Pruned bad csets
# 'pruned' is all csets whose fate is already known: good, bad, skip
skips = 'bisect(skip)' # Pruned skipped csets
pruned = '( (%s) | (%s) | (%s) )' % (goods, bads, skips)
# 'untested' is all cset that are- in 'range', but not in 'pruned'
untested = '( (%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 = '::bisect(bad) - ::bisect(good)' # Ignored bads' ancestors
iga = '::bisect(good) - ::bisect(bad)' # Ignored goods' ancestors
ignored = '( ( (%s) | (%s) ) - (%s) )' % (iba, iga, range)
if status == 'range':
return repo.revs(range)
elif status == 'pruned':
return repo.revs(pruned)
elif status == 'untested':
return repo.revs(untested)
elif status == 'ignored':
return repo.revs(ignored)
elif status == "goods":
return repo.revs(goods)
elif status == "bads":
return repo.revs(bads)
else:
raise error.ParseError(_('invalid bisect state'))
def label(repo, node):
rev = repo.changelog.rev(node)
# Try explicit sets
if rev in get(repo, 'good'):
# i18n: bisect changeset status
return _('good')
if rev in get(repo, 'bad'):
# i18n: bisect changeset status
return _('bad')
if rev in get(repo, 'skip'):
# i18n: bisect changeset status
return _('skipped')
if rev in get(repo, 'untested') or rev in get(repo, 'current'):
# i18n: bisect changeset status
return _('untested')
if rev in get(repo, 'ignored'):
# i18n: bisect changeset status
return _('ignored')
# Try implicit sets
if rev in get(repo, 'goods'):
# i18n: bisect changeset status
return _('good (implicit)')
if rev in get(repo, 'bads'):
# i18n: bisect changeset status
return _('bad (implicit)')
return None
def shortlabel(label):
if label:
return label[0].upper()
return None
def printresult(ui, repo, state, displayer, nodes, good):
if len(nodes) == 1:
# narrowed it down to a single revision
if good:
ui.write(_("The first good revision is:\n"))
else:
ui.write(_("The first bad revision is:\n"))
displayer.show(repo[nodes[0]])
extendnode = extendrange(repo, state, nodes, good)
if extendnode is not None:
ui.write(_('Not all ancestors of this changeset have been'
' checked.\nUse bisect --extend to continue the '
'bisection from\nthe common ancestor, %s.\n')
% extendnode)
else:
# multiple possible revisions
if good:
ui.write(_("Due to skipped revisions, the first "
"good revision could be any of:\n"))
else:
ui.write(_("Due to skipped revisions, the first "
"bad revision could be any of:\n"))
for n in nodes:
displayer.show(repo[n])
displayer.close()