view hgext/graphlog.py @ 42354:dbd0fcca6dfc

discovery: slowly increase sampling size

Some pathological discovery runs can requires many roundtrip. When this happens
things can get very slow.

To make the algorithm more resilience again such pathological case. We slowly
increase the sample size with each roundtrip (+5%). This will have a negligible
impact on "normal" discovery with few roundtrips, but a large positive impact of
case with many roundtrips. Asking more question per roundtrip helps to reduce
the undecided set faster. Instead of reducing the undecided set a linear speed
(in the worst case), we reduce it as a guaranteed (small) exponential rate. The
data below show this slow ramp up in sample size:

round trip    |    1 |     5 |    10 |    20 |     50 |     100 |       130 |
sample size   |  200 |   254 |   321 |   517 |  2 199 |  25 123 |   108 549 |
covered nodes |  200 | 1 357 | 2 821 | 7 031 | 42 658 | 524 530 | 2 276 755 |

To be a bit more concrete, lets take a very pathological case as an example. We
are doing discovery from a copy of Mozilla-try to a more recent version of
mozilla-unified. Mozilla-unified heads are unknown to the mozilla-try repo and
there are over 1 million "missing" changesets. (the discovery is "local" to
avoid network interference)

Without this change, the discovery:
- last 1858 seconds (31 minutes),
- does 1700 round trip,
- asking about 340 000 nodes.

With this change, the discovery:
- last 218 seconds (3 minutes, 38 seconds a -88% improvement),
- does 94 round trip (-94%),
- asking about 344 211 nodes (+1%).

Of course, this is an extreme case (and 3 minutes is still slow). However this
give a good example of how this sample size increase act as a safety net
catching any bad situations.

We could image a steeper increase than 5%. For example 10% would give the
following number:

round trip    |    1 |     5 |    10 |     20 |     50  |        75 |        100 |
sample size   |  200 |   321 |   514 |  1 326 |  23 060 |   249 812 |  2 706 594 |
covered nodes |  200 | 1 541 | 3 690 | 12 671 | 251 871 | 2 746 254 | 29 770 966 |

In parallel, it is useful to understand these pathological cases and improve
them. However the current change provides a general purpose safety net to smooth
the impact of pathological cases.

To avoid issue with older http server, the increase in sample size only occurs
if the protocol has not limit on command argument size.

# ASCII graph log extension for Mercurial
#
# Copyright 2007 Joel Rosdahl <[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.

'''command to view revision graphs from a shell (DEPRECATED)

The functionality of this extension has been include in core Mercurial
since version 2.3. Please use :hg:`log -G ...` instead.

This extension adds a --graph option to the incoming, outgoing and log
commands. When this options is given, an ASCII representation of the
revision graph is also shown.
'''

from __future__ import absolute_import

from mercurial.i18n import _
from mercurial import (
    cmdutil,
    commands,
    registrar,
)

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('glog',
    [('f', 'follow', None,
     _('follow changeset history, or file history across copies and renames')),
    ('', 'follow-first', None,
     _('only follow the first parent of merge changesets (DEPRECATED)')),
    ('d', 'date', '', _('show revisions matching date spec'), _('DATE')),
    ('C', 'copies', None, _('show copied files')),
    ('k', 'keyword', [],
     _('do case-insensitive search for a given text'), _('TEXT')),
    ('r', 'rev', [], _('show the specified revision or revset'), _('REV')),
    ('', 'removed', None, _('include revisions where files were removed')),
    ('m', 'only-merges', None, _('show only merges (DEPRECATED)')),
    ('u', 'user', [], _('revisions committed by user'), _('USER')),
    ('', 'only-branch', [],
     _('show only changesets within the given named branch (DEPRECATED)'),
     _('BRANCH')),
    ('b', 'branch', [],
     _('show changesets within the given named branch'), _('BRANCH')),
    ('P', 'prune', [],
     _('do not display revision or any of its ancestors'), _('REV')),
    ] + cmdutil.logopts + cmdutil.walkopts,
    _('[OPTION]... [FILE]'),
    helpcategory=command.CATEGORY_CHANGE_NAVIGATION,
    inferrepo=True)
def glog(ui, repo, *pats, **opts):
    """show revision history alongside an ASCII revision graph

    Print a revision history alongside a revision graph drawn with
    ASCII characters.

    Nodes printed as an @ character are parents of the working
    directory.

    This is an alias to :hg:`log -G`.
    """
    opts[r'graph'] = True
    return commands.log(ui, repo, *pats, **opts)