view hgext/split.py @ 42743:8c9a6adec67a

rust-discovery: using the children cache in add_missing

The DAG range computation often needs to get back to very old
revisions, and turns out to be disproportionately long, given
that the end goal is to remove the descendents of the given
missing revisons from the undecided set.

The fast iteration capabilities available in the Rust case make
it possible to avoid the DAG range entirely, at the cost of
precomputing the children cache, and to simply iterate on
children of the given missing revisions.

This is a case where staying on the same side of the interface
between the two languages has clear benefits.

On discoveries with initial undecided sets
small enough to bypass sampling entirely, the total cost of
computing the children cache and the subsequent iteration
becomes better than the Python + C counterpart, which relies on
reachableroots2.

For example, on a repo with more than one million revisions with
an initial undecided set of 11 elements, we get these figures:

Rust version with simple iteration
  addcommons: 57.287us
  first undecided computation: 184.278334ms
  first children cache computation: 131.056us
  addmissings iteration: 42.766us
  first addinfo total: 185.24 ms

Python + C version
  first addcommons: 0.29 ms
  addcommons 0.21 ms
  first undecided computation 191.35 ms
  addmissings 45.75 ms
  first addinfo total: 237.77 ms

On discoveries with large undecided sets, the initial price paid
makes the first addinfo slower than the Python + C version,
but that's more than compensated by the gain in sampling and
subsequent iterations.
Here's an extreme example with an undecided set of a million revisions:

Rust version:
  first undecided computation: 293.842629ms
  first children cache computation: 407.911297ms
  addmissings iteration: 34.312869ms
  first addinfo total: 776.02 ms
  taking initial sample
  query 2: sampling time: 1318.38 ms
  query 2; still undecided: 1005013, sample size is: 200
  addmissings: 143.062us

Python + C version:
  first undecided computation 298.13 ms
  addmissings 80.13 ms
  first addinfo total: 399.62 ms
  taking initial sample
  query 2: sampling time: 3957.23 ms
  query 2; still undecided: 1005013, sample size is: 200
  addmissings 52.88 ms

Differential Revision: https://phab.mercurial-scm.org/D6428

# split.py - split a changeset into smaller ones
#
# Copyright 2015 Laurent Charignon <[e-mail]>
# Copyright 2017 Facebook, Inc.
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
"""command to split a changeset into smaller ones (EXPERIMENTAL)"""

from __future__ import absolute_import

from mercurial.i18n import _

from mercurial.node import (
    nullid,
    short,
)

from mercurial import (
    bookmarks,
    cmdutil,
    commands,
    error,
    hg,
    obsolete,
    phases,
    pycompat,
    registrar,
    revsetlang,
    scmutil,
)

# allow people to use split without explicitly enabling rebase extension
from . import (
    rebase,
)

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('split',
    [('r', 'rev', '', _("revision to split"), _('REV')),
     ('', 'rebase', True, _('rebase descendants after split')),
    ] + cmdutil.commitopts2,
    _('hg split [--no-rebase] [[-r] REV]'),
    helpcategory=command.CATEGORY_CHANGE_MANAGEMENT, helpbasic=True)
def split(ui, repo, *revs, **opts):
    """split a changeset into smaller ones

    Repeatedly prompt changes and commit message for new changesets until there
    is nothing left in the original changeset.

    If --rev was not given, split the working directory parent.

    By default, rebase connected non-obsoleted descendants onto the new
    changeset. Use --no-rebase to avoid the rebase.
    """
    opts = pycompat.byteskwargs(opts)
    revlist = []
    if opts.get('rev'):
        revlist.append(opts.get('rev'))
    revlist.extend(revs)
    with repo.wlock(), repo.lock(), repo.transaction('split') as tr:
        revs = scmutil.revrange(repo, revlist or ['.'])
        if len(revs) > 1:
            raise error.Abort(_('cannot split multiple revisions'))

        rev = revs.first()
        ctx = repo[rev]
        if rev is None or ctx.node() == nullid:
            ui.status(_('nothing to split\n'))
            return 1
        if ctx.node() is None:
            raise error.Abort(_('cannot split working directory'))

        # rewriteutil.precheck is not very useful here because:
        # 1. null check is done above and it's more friendly to return 1
        #    instead of abort
        # 2. mergestate check is done below by cmdutil.bailifchanged
        # 3. unstable check is more complex here because of --rebase
        #
        # So only "public" check is useful and it's checked directly here.
        if ctx.phase() == phases.public:
            raise error.Abort(_('cannot split public changeset'),
                              hint=_("see 'hg help phases' for details"))

        descendants = list(repo.revs('(%d::) - (%d)', rev, rev))
        alloworphaned = obsolete.isenabled(repo, obsolete.allowunstableopt)
        if opts.get('rebase'):
            # Skip obsoleted descendants and their descendants so the rebase
            # won't cause conflicts for sure.
            torebase = list(repo.revs('%ld - (%ld & obsolete())::',
                                      descendants, descendants))
            if not alloworphaned and len(torebase) != len(descendants):
                raise error.Abort(_('split would leave orphaned changesets '
                                    'behind'))
        else:
            if not alloworphaned and descendants:
                raise error.Abort(
                    _('cannot split changeset with children without rebase'))
            torebase = ()

        if len(ctx.parents()) > 1:
            raise error.Abort(_('cannot split a merge changeset'))

        cmdutil.bailifchanged(repo)

        # Deactivate bookmark temporarily so it won't get moved unintentionally
        bname = repo._activebookmark
        if bname and repo._bookmarks[bname] != ctx.node():
            bookmarks.deactivate(repo)

        wnode = repo['.'].node()
        top = None
        try:
            top = dosplit(ui, repo, tr, ctx, opts)
        finally:
            # top is None: split failed, need update --clean recovery.
            # wnode == ctx.node(): wnode split, no need to update.
            if top is None or wnode != ctx.node():
                hg.clean(repo, wnode, show_stats=False)
            if bname:
                bookmarks.activate(repo, bname)
        if torebase and top:
            dorebase(ui, repo, torebase, top)

def dosplit(ui, repo, tr, ctx, opts):
    committed = [] # [ctx]

    # Set working parent to ctx.p1(), and keep working copy as ctx's content
    if ctx.node() != repo.dirstate.p1():
        hg.clean(repo, ctx.node(), show_stats=False)
    with repo.dirstate.parentchange():
        scmutil.movedirstate(repo, ctx.p1())

    # Any modified, added, removed, deleted result means split is incomplete
    incomplete = lambda repo: any(repo.status()[:4])

    # Main split loop
    while incomplete(repo):
        if committed:
            header = (_('HG: Splitting %s. So far it has been split into:\n')
                      % short(ctx.node()))
            for c in committed:
                firstline = c.description().split('\n', 1)[0]
                header += _('HG: - %s: %s\n') % (short(c.node()), firstline)
            header += _('HG: Write commit message for the next split '
                        'changeset.\n')
        else:
            header = _('HG: Splitting %s. Write commit message for the '
                       'first split changeset.\n') % short(ctx.node())
        opts.update({
            'edit': True,
            'interactive': True,
            'message': header + ctx.description(),
        })
        commands.commit(ui, repo, **pycompat.strkwargs(opts))
        newctx = repo['.']
        committed.append(newctx)

    if not committed:
        raise error.Abort(_('cannot split an empty revision'))

    scmutil.cleanupnodes(repo, {ctx.node(): [c.node() for c in committed]},
                         operation='split', fixphase=True)

    return committed[-1]

def dorebase(ui, repo, src, destctx):
    rebase.rebase(ui, repo, rev=[revsetlang.formatspec('%ld', src)],
                  dest=revsetlang.formatspec('%d', destctx.rev()))