Mercurial > hgsubversion
view README @ 1233:0d0132cba155
editor: fix edge case with in memory file-store size limit
There are a few cases where we will set a single file into to the
editor's FileStore object more than once. Notably, for copied and
then modified files, we will set it at least twice. Three times if
editing fails (which it can for symlinks).
If we pass the in-memory storage limit in between the first (or second
if editing fails) time we set the file and the last time we set the
file, we will write the data to the in memory store the first time and
the file store the last time. We didn't remove it form the in-memory
store though, and we always prefer reading from the in-memory store.
This means we can sometimes end up with the wrong version of a file.
This is fairly unlikely to happen in normal use since you need to hit
the memory limit between two writes to the store for the same file.
We only write a file multiple times if a) the file (and not one of
it's parent directories) is copied and then modified or b) editing
fails. From what I can tell, it's only common for editing to fail for
symlinks, and they ten to be relatively small data that is unlikely to
push over the limit. Finally, the default limit is 100MB which I
would expect to be most often either well over (source code) or well
under (binaries or automated changes) the size of the changes files in
a single commit.
The easiest way to reproduce this is to set the in-memory cache size
to 0 and then commit a copied and modified symlink. The empty-string
version from the failed editing will be the one that persists. I
happened to stumble upon this while trying (and failing) to test a
bug-fix for a related bug with identical symptoms (empty simlink). I
have seen this in the wild, once, but couldn't reproduce it at the
time. The repo in question is quite large and quite active, so I am
quite confident in my estimation that this is a real, but very rare,
problem.
The test changes attached to this was mneant to test a related bug,
but turned out not to actually cover the bug in question. They did
trigger this bug though, and are worthwhile to test, so I kept them.
| author | David Schleimer <dschleimer@fb.com> |
|---|---|
| date | Mon, 07 Apr 2014 17:51:59 -0700 |
| parents | 3df6ed4e7561 |
| children | b06be5815692 |
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.. -*-restructuredtext-*- ============ hgsubversion ============ hgsubversion is an extension for Mercurial that allows using Mercurial as a Subversion client. At this point, hgsubversion is usable by users reasonably familiar with Mercurial as a VCS. It's not recommended to dive into hgsubversion as an introduction to Mercurial, since hgsubversion "bends the rules" a little and violates some of the typical assumptions of early Mercurial users. Installation ------------ You need to have either have Subversion 1.5 (or later) installed along with either Subvertpy 0.7.4 (or later) or the Subversion SWIG Python bindings. You need Mercurial 2.0 or later. .. _mercurial: http://selenic.com/repo/hg .. _mercurial-stable: http://selenic.com/repo/hg-stable .. _crew: http://hg.intevation.org/mercurial/crew .. _crew-stable: http://hg.intevation.org/mercurial/crew-stable If you are unfamiliar with installing Mercurial extensions, please see the UsingExtensions_ page in the Mercurial wiki. Look at the example for specifying an absolute path near the bottom of the page. You want to give the path to the top level of your clone of this repository. .. _UsingExtensions: http://mercurial.selenic.com/wiki/UsingExtensions Before using hgsubversion, I *strongly* encourage you to run the automated tests. Just use nose_ if you have it (or ``easy_install nose`` if you want it), or use ``python tests/run.py`` to run the suite with the conventional test runner. Note that because I use nose, there's a lot of stdout spew in the tests right now. The important part is that all the tests pass. .. _nose: http://code.google.com/p/python-nose/ You can check that hgsubversion is installed and properly activated using the following command:: $ hg version --svn Mercurial Distributed SCM (version ...) Copyright (C) 2005-2010 Matt Mackall <mpm@selenic.com> and others This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. hgsubversion: ... Subversion: ... bindings: Subvertpy ... If your bindings are listed as `SWIG`, please consider installing Subvertpy_. .. _Subvertpy: http://pypi.python.org/pypi/subvertpy Further Reading --------------- More information on how to use hgsubversion is available from within Mercurial in the `subversion` help topic. To view it, use:: $ hg help subversion The Restructured Text source for this topic is also available in the file ``hgsubverson/help/subversion.rst``.