revlog: introduce an experimental flag to slice chunks reads when too sparse
Delta chains can become quite sparse if there is a lot of unrelated data between
relevant pieces. Right now, revlog always reads all the necessary data for the
delta chain in one single read. This can lead to a lot of unrelated data to be
read (see
issue5482 for more details).
One can use the `experimental.maxdeltachainspan` option with a large value
(or -1) to easily produce a very sparse delta chain.
This change introduces the ability to slice the chunks retrieval into multiple
reads, skipping large sections of unrelated data. Preliminary testing shows
interesting results. For example the peak memory consumption to read a manifest
on a large repository is reduced from 600MB to 250MB (200MB without
maxdeltachainspan). However, the slicing itself and the multiple reads can have
an negative impact on performance. This is why the new feature is hidden behind
an experimental flag.
Future changesets will add various parameters to control the slicing heuristics.
We hope to experiment a wide variety of repositories during 4.4 and hopefully
turn the feature on by default in 4.5.
As a first try, the algorithm itself is prone to deep changes. However, we wish
to define APIs and have a baseline to work on.
# fetch.py - pull and merge remote changes
#
# Copyright 2006 Vadim Gelfer <vadim.gelfer@gmail.com>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
'''pull, update and merge in one command (DEPRECATED)'''
from __future__ import absolute_import
from mercurial.i18n import _
from mercurial.node import (
short,
)
from mercurial import (
cmdutil,
error,
exchange,
hg,
lock,
registrar,
util,
)
release = lock.release
cmdtable = {}
command = registrar.command(cmdtable)
# Note for extension authors: ONLY specify testedwith = 'ships-with-hg-core' for
# extensions which SHIP WITH MERCURIAL. Non-mainline extensions should
# be specifying the version(s) of Mercurial they are tested with, or
# leave the attribute unspecified.
testedwith = 'ships-with-hg-core'
@command('fetch',
[('r', 'rev', [],
_('a specific revision you would like to pull'), _('REV')),
('', 'edit', None, _('invoke editor on commit messages')),
('', 'force-editor', None, _('edit commit message (DEPRECATED)')),
('', 'switch-parent', None, _('switch parents when merging')),
] + cmdutil.commitopts + cmdutil.commitopts2 + cmdutil.remoteopts,
_('hg fetch [SOURCE]'))
def fetch(ui, repo, source='default', **opts):
'''pull changes from a remote repository, merge new changes if needed.
This finds all changes from the repository at the specified path
or URL and adds them to the local repository.
If the pulled changes add a new branch head, the head is
automatically merged, and the result of the merge is committed.
Otherwise, the working directory is updated to include the new
changes.
When a merge is needed, the working directory is first updated to
the newly pulled changes. Local changes are then merged into the
pulled changes. To switch the merge order, use --switch-parent.
See :hg:`help dates` for a list of formats valid for -d/--date.
Returns 0 on success.
'''
date = opts.get('date')
if date:
opts['date'] = util.parsedate(date)
parent, _p2 = repo.dirstate.parents()
branch = repo.dirstate.branch()
try:
branchnode = repo.branchtip(branch)
except error.RepoLookupError:
branchnode = None
if parent != branchnode:
raise error.Abort(_('working directory not at branch tip'),
hint=_("use 'hg update' to check out branch tip"))
wlock = lock = None
try:
wlock = repo.wlock()
lock = repo.lock()
cmdutil.bailifchanged(repo)
bheads = repo.branchheads(branch)
bheads = [head for head in bheads if len(repo[head].children()) == 0]
if len(bheads) > 1:
raise error.Abort(_('multiple heads in this branch '
'(use "hg heads ." and "hg merge" to merge)'))
other = hg.peer(repo, opts, ui.expandpath(source))
ui.status(_('pulling from %s\n') %
util.hidepassword(ui.expandpath(source)))
revs = None
if opts['rev']:
try:
revs = [other.lookup(rev) for rev in opts['rev']]
except error.CapabilityError:
err = _("other repository doesn't support revision lookup, "
"so a rev cannot be specified.")
raise error.Abort(err)
# Are there any changes at all?
modheads = exchange.pull(repo, other, heads=revs).cgresult
if modheads == 0:
return 0
# Is this a simple fast-forward along the current branch?
newheads = repo.branchheads(branch)
newchildren = repo.changelog.nodesbetween([parent], newheads)[2]
if len(newheads) == 1 and len(newchildren):
if newchildren[0] != parent:
return hg.update(repo, newchildren[0])
else:
return 0
# Are there more than one additional branch heads?
newchildren = [n for n in newchildren if n != parent]
newparent = parent
if newchildren:
newparent = newchildren[0]
hg.clean(repo, newparent)
newheads = [n for n in newheads if n != newparent]
if len(newheads) > 1:
ui.status(_('not merging with %d other new branch heads '
'(use "hg heads ." and "hg merge" to merge them)\n') %
(len(newheads) - 1))
return 1
if not newheads:
return 0
# Otherwise, let's merge.
err = False
if newheads:
# By default, we consider the repository we're pulling
# *from* as authoritative, so we merge our changes into
# theirs.
if opts['switch_parent']:
firstparent, secondparent = newparent, newheads[0]
else:
firstparent, secondparent = newheads[0], newparent
ui.status(_('updating to %d:%s\n') %
(repo.changelog.rev(firstparent),
short(firstparent)))
hg.clean(repo, firstparent)
ui.status(_('merging with %d:%s\n') %
(repo.changelog.rev(secondparent), short(secondparent)))
err = hg.merge(repo, secondparent, remind=False)
if not err:
# we don't translate commit messages
message = (cmdutil.logmessage(ui, opts) or
('Automated merge with %s' %
util.removeauth(other.url())))
editopt = opts.get('edit') or opts.get('force_editor')
editor = cmdutil.getcommiteditor(edit=editopt, editform='fetch')
n = repo.commit(message, opts['user'], opts['date'], editor=editor)
ui.status(_('new changeset %d:%s merges remote changes '
'with local\n') % (repo.changelog.rev(n),
short(n)))
return err
finally:
release(lock, wlock)