##// END OF EJS Templates
snapshot: search for unrelated but reusable full-snapshot...
snapshot: search for unrelated but reusable full-snapshot # New Strategy Step: Reusing Snapshot Outside Of Parents' Chain. If no suitable bases were found in the parent's chains, see if we could reuse a full snapshot not directly related to the current revision. Such search can be expensive, so we only search for snapshots appended to the revlog *after* the bases used by the parents of the current revision (the one we just tested). We assume the parent's bases were created because the previous snapshots were unsuitable, so there are low odds they would be useful now. This search gives a chance to reuse a delta chain unrelated to the current revision. Without this re-use, topological branches would keep reopening new full chains. Creating more and more snapshots as the repository grow. In repositories with many topological branches, the lack of delta reuse can create too many snapshots reducing overall compression to nothing. This results in a very large repository and other usability issues. For now, we still focus on creating level-1 snapshots. However, this principle will play a large part in how we avoid snapshot explosion once we have more snapshot levels. # Effects On The Test Repository In the test repository we created, we can see the beneficial effect of such reuse. We need very few level-0 snapshots and the overall revlog size has decreased. The `hg debugrevlog` call, show a "lvl-2" snapshot. It comes from the existing delta logic using the `prev` revision (revlog's tip) as the base. In this specific case, it turns out the tip was a level-1 snapshot. This is a coincidence that can be ignored. Finding and testing against all these unrelated snapshots can have a performance impact at write time. We currently focus on building good deltas chain we build. Performance concern will be dealt with later in another series.

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rcutil.py
98 lines | 3.1 KiB | text/x-python | PythonLexer
# rcutil.py - utilities about config paths, special config sections etc.
#
# Copyright Mercurial Contributors
#
# 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 os
from . import (
encoding,
pycompat,
util,
)
if pycompat.iswindows:
from . import scmwindows as scmplatform
else:
from . import scmposix as scmplatform
fallbackpager = scmplatform.fallbackpager
systemrcpath = scmplatform.systemrcpath
userrcpath = scmplatform.userrcpath
def _expandrcpath(path):
'''path could be a file or a directory. return a list of file paths'''
p = util.expandpath(path)
if os.path.isdir(p):
join = os.path.join
return [join(p, f) for f, k in util.listdir(p) if f.endswith('.rc')]
return [p]
def envrcitems(env=None):
'''Return [(section, name, value, source)] config items.
The config items are extracted from environment variables specified by env,
used to override systemrc, but not userrc.
If env is not provided, encoding.environ will be used.
'''
if env is None:
env = encoding.environ
checklist = [
('EDITOR', 'ui', 'editor'),
('VISUAL', 'ui', 'editor'),
('PAGER', 'pager', 'pager'),
]
result = []
for envname, section, configname in checklist:
if envname not in env:
continue
result.append((section, configname, env[envname], '$%s' % envname))
return result
def defaultrcpath():
'''return rc paths in default.d'''
path = []
defaultpath = os.path.join(util.datapath, 'default.d')
if os.path.isdir(defaultpath):
path = _expandrcpath(defaultpath)
return path
def rccomponents():
'''return an ordered [(type, obj)] about where to load configs.
respect $HGRCPATH. if $HGRCPATH is empty, only .hg/hgrc of current repo is
used. if $HGRCPATH is not set, the platform default will be used.
if a directory is provided, *.rc files under it will be used.
type could be either 'path' or 'items', if type is 'path', obj is a string,
and is the config file path. if type is 'items', obj is a list of (section,
name, value, source) that should fill the config directly.
'''
envrc = ('items', envrcitems())
if 'HGRCPATH' in encoding.environ:
# assume HGRCPATH is all about user configs so environments can be
# overridden.
_rccomponents = [envrc]
for p in encoding.environ['HGRCPATH'].split(pycompat.ospathsep):
if not p:
continue
_rccomponents.extend(('path', p) for p in _expandrcpath(p))
else:
normpaths = lambda paths: [('path', os.path.normpath(p)) for p in paths]
_rccomponents = normpaths(defaultrcpath() + systemrcpath())
_rccomponents.append(envrc)
_rccomponents.extend(normpaths(userrcpath()))
return _rccomponents
def defaultpagerenv():
'''return a dict of default environment variables and their values,
intended to be set before starting a pager.
'''
return {'LESS': 'FRX', 'LV': '-c'}