##// END OF EJS Templates
revlog: add a mechanism to verify expected file position before appending...
revlog: add a mechanism to verify expected file position before appending If someone uses `hg debuglocks`, or some non-hg process writes to the .hg directory without respecting the locks, or if the repo's on a networked filesystem, it's possible for the revlog code to write out corrupted data. The form of this corruption can vary depending on what data was written and how that happened. We are in the "networked filesystem" case (though I've had users also do this to themselves with the "`hg debuglocks`" scenario), and most often see this with the changelog. What ends up happening is we produce two items (let's call them rev1 and rev2) in the .i file that have the same linkrev, baserev, and offset into the .d file, while the data in the .d file is appended properly. rev2's compressed_size is accurate for rev2, but when we go to decompress the data in the .d file, we use the offset that's recorded in the index file, which is the same as rev1, and attempt to decompress rev2.compressed_size bytes of rev1's data. This usually does not succeed. :) When using inline data, this also fails, though I haven't investigated why too closely. This shows up as a "patch decode" error. I believe what's happening there is that we're basically ignoring the offset field, getting the data properly, but since baserev != rev, it thinks this is a delta based on rev (instead of a full text) and can't actually apply it as such. For now, I'm going to make this an optional component and default it to entirely off. I may increase the default severity of this in the future, once I've enabled it for my users and we gain more experience with it. Luckily, most of my users have a versioned filesystem and can roll back to before the corruption has been written, it's just a hassle to do so and not everyone knows how (so it's a support burden). Users on other filesystems will not have that luxury, and this can cause them to have a corrupted repository that they are unlikely to know how to resolve, and they'll see this as a data-loss event. Refusing to create the corruption is a much better user experience. This mechanism is not perfect. There may be false-negatives (racy writes that are not detected). There should not be any false-positives (non-racy writes that are detected as such). This is not a mechanism that makes putting a repo on a networked filesystem "safe" or "supported", just *less* likely to cause corruption. Differential Revision: https://phab.mercurial-scm.org/D9952

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__init__.py
78 lines | 2.4 KiB | text/x-python | PythonLexer
# __init__.py - narrowhg extension
#
# Copyright 2017 Google, Inc.
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
'''create clones which fetch history data for subset of files (EXPERIMENTAL)'''
from __future__ import absolute_import
from mercurial import (
localrepo,
registrar,
requirements,
)
from . import (
narrowbundle2,
narrowcommands,
narrowrepo,
narrowtemplates,
narrowwirepeer,
)
# 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 = b'ships-with-hg-core'
configtable = {}
configitem = registrar.configitem(configtable)
# Narrowhg *has* support for serving ellipsis nodes (which are used at
# least by Google's internal server), but that support is pretty
# fragile and has a lot of problems on real-world repositories that
# have complex graph topologies. This could probably be corrected, but
# absent someone needing the full support for ellipsis nodes in
# repositories with merges, it's unlikely this work will get done. As
# of this writining in late 2017, all repositories large enough for
# ellipsis nodes to be a hard requirement also enforce strictly linear
# history for other scaling reasons.
configitem(
b'experimental',
b'narrowservebrokenellipses',
default=False,
alias=[(b'narrow', b'serveellipses')],
)
# Export the commands table for Mercurial to see.
cmdtable = narrowcommands.table
def featuresetup(ui, features):
features.add(requirements.NARROW_REQUIREMENT)
def uisetup(ui):
"""Wraps user-facing mercurial commands with narrow-aware versions."""
localrepo.featuresetupfuncs.add(featuresetup)
narrowbundle2.setup()
narrowcommands.setup()
narrowwirepeer.uisetup()
def reposetup(ui, repo):
"""Wraps local repositories with narrow repo support."""
if not repo.local():
return
repo.ui.setconfig(b'experimental', b'narrow', True, b'narrow-ext')
if requirements.NARROW_REQUIREMENT in repo.requirements:
narrowrepo.wraprepo(repo)
narrowwirepeer.reposetup(repo)
templatekeyword = narrowtemplates.templatekeyword
revsetpredicate = narrowtemplates.revsetpredicate