view mercurial/rewriteutil.py @ 40445:634b45317459 stable

changegroup: restore default node ordering (issue6001)

Changeset db5501d9 changed the default node ordering from "storage" to
"linearize".

While the new API is more explicit and cleaner, the "linearize" order is
problematic on certain repositories like netbeans where it makes bundling
slower the more nodes we bundle.

Pushing and pulling 100 changesets was ~20% slower and pushing and pulling
1000 changesets was ~600% slower.

A very quick analysis of profile traces showed that the pull operation was
taking more time creating the delta.

Putting back the old default order seems to be the safe option. With more time
during the next cycle, we can understand better the impact of sorting with the
DAG order by default, the source of the regression and how to mitigate it.

/!\ We are still waiting for the full performance impact but with this patch,
bundling and pulling locally (not on the performance workstation) 1000
changesets on the netbeans repository is as fast as before the regression.

Differential Revision: https://phab.mercurial-scm.org/D5196

# rewriteutil.py - utility functions for rewriting changesets
#
# Copyright 2017 Octobus <[e-mail]>
#
# 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

from .i18n import _

from . import (
    error,
    node,
    obsolete,
    revset,
)

def precheck(repo, revs, action='rewrite'):
    """check if revs can be rewritten
    action is used to control the error message.

    Make sure this function is called after taking the lock.
    """
    if node.nullrev in revs:
        msg = _("cannot %s null changeset") % (action)
        hint = _("no changeset checked out")
        raise error.Abort(msg, hint=hint)

    publicrevs = repo.revs('%ld and public()', revs)
    if len(repo[None].parents()) > 1:
        raise error.Abort(_("cannot %s while merging") % action)

    if publicrevs:
        msg = _("cannot %s public changesets") % (action)
        hint = _("see 'hg help phases' for details")
        raise error.Abort(msg, hint=hint)

    newunstable = disallowednewunstable(repo, revs)
    if newunstable:
        raise error.Abort(_("cannot %s changeset with children") % action)

def disallowednewunstable(repo, revs):
    """Checks whether editing the revs will create new unstable changesets and
    are we allowed to create them.

    To allow new unstable changesets, set the config:
        `experimental.evolution.allowunstable=True`
    """
    allowunstable = obsolete.isenabled(repo, obsolete.allowunstableopt)
    if allowunstable:
        return revset.baseset()
    return repo.revs("(%ld::) - %ld", revs, revs)