xdiff: add a preprocessing step that trims files
xdiff has a `xdl_trim_ends` step that removes common lines, unmatchable
lines. That is in theory good, but happens too late - after splitting,
hashing, and adjusting the hash values so they are unique. Those splitting,
hashing and adjusting hash values steps could have noticeable overhead.
Diffing two large files with minor (one-line-ish) changes are not uncommon.
In that case, the raw performance of those preparation steps seriously
matter. Even allocating an O(N) array and storing line offsets to it is
expensive. Therefore my previous attempts [1] [2] cannot be good enough
since they do not remove the O(N) array assignment.
This patch adds a preprocessing step - `xdl_trim_files` that runs before
other preprocessing steps. It counts common prefix and suffix and lines in
them (needed for displaying line number), without doing anything else.
Testing with a crafted large (169MB) file, with minor change:
```
open('a','w').write(''.join('%s\n' % (i % 100000) for i in xrange(
30000000) if i != 6000000))
open('b','w').write(''.join('%s\n' % (i % 100000) for i in xrange(
30000000) if i != 6003000))
```
Running xdiff by a simple binary [3], this patch improves the xdiff perf by
more than 10x for the above case:
```
# xdiff before this patch
2.41s user 1.13s system 98% cpu 3.592 total
# xdiff after this patch
0.14s user 0.16s system 98% cpu 0.309 total
# gnu diffutils
0.12s user 0.15s system 98% cpu 0.272 total
# (best of 20 runs)
```
It's still slightly slower than GNU diffutils. But it's pretty close now.
Testing with real repo data:
For the whole repo, this patch makes xdiff 25% faster:
```
# hg perfbdiff --count 100 --alldata -c
d334afc585e2 --blocks [--xdiff]
# xdiff, after
! wall 0.058861 comb 0.050000 user 0.050000 sys 0.000000 (best of 100)
# xdiff, before
! wall 0.077816 comb 0.080000 user 0.080000 sys 0.000000 (best of 91)
# bdiff
! wall 0.117473 comb 0.120000 user 0.120000 sys 0.000000 (best of 67)
```
For files that are long (ex. commands.py), the speedup is more than 3x, very
significant:
```
# hg perfbdiff --count 3000 --blocks commands.py.i 1 [--xdiff]
# xdiff, after
! wall 0.690583 comb 0.690000 user 0.690000 sys 0.000000 (best of 12)
# xdiff, before
! wall 2.240361 comb 2.210000 user 2.210000 sys 0.000000 (best of 4)
# bdiff
! wall 2.469852 comb 2.440000 user 2.440000 sys 0.000000 (best of 4)
```
[1]: https://phab.mercurial-scm.org/D2631
[2]: https://phab.mercurial-scm.org/D2634
[3]:
```
// Code to run xdiff from command line. No proper error handling.
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include "mercurial/thirdparty/xdiff/xdiff.h"
#define ensure(x) if (!(x)) exit(255);
mmfile_t readfile(const char *path) {
struct stat st; int fd = open(path, O_RDONLY);
fstat(fd, &st); mmfile_t file = { malloc(st.st_size), st.st_size };
ensure(read(fd, file.ptr, st.st_size) == st.st_size); close(fd);
return file;
}
int main(int argc, char const *argv[]) {
mmfile_t a = readfile(argv[1]), b = readfile(argv[2]);
xpparam_t xpp = {0}; xdemitconf_t xecfg = {0}; xdemitcb_t ecb = {0};
xdl_diff(&a, &b, &xpp, &xecfg, &ecb);
return 0;
}
```
Differential Revision: https://phab.mercurial-scm.org/D2686
# Copyright 2006, 2007 Matt Mackall <mpm@selenic.com>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
'''share a common history between several working directories
Automatic Pooled Storage for Clones
-----------------------------------
When this extension is active, :hg:`clone` can be configured to
automatically share/pool storage across multiple clones. This
mode effectively converts :hg:`clone` to :hg:`clone` + :hg:`share`.
The benefit of using this mode is the automatic management of
store paths and intelligent pooling of related repositories.
The following ``share.`` config options influence this feature:
``share.pool``
Filesystem path where shared repository data will be stored. When
defined, :hg:`clone` will automatically use shared repository
storage instead of creating a store inside each clone.
``share.poolnaming``
How directory names in ``share.pool`` are constructed.
"identity" means the name is derived from the first changeset in the
repository. In this mode, different remotes share storage if their
root/initial changeset is identical. In this mode, the local shared
repository is an aggregate of all encountered remote repositories.
"remote" means the name is derived from the source repository's
path or URL. In this mode, storage is only shared if the path or URL
requested in the :hg:`clone` command matches exactly to a repository
that was cloned before.
The default naming mode is "identity".
'''
from __future__ import absolute_import
import errno
from mercurial.i18n import _
from mercurial import (
bookmarks,
commands,
error,
extensions,
hg,
registrar,
txnutil,
util,
)
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('share',
[('U', 'noupdate', None, _('do not create a working directory')),
('B', 'bookmarks', None, _('also share bookmarks')),
('', 'relative', None, _('point to source using a relative path '
'(EXPERIMENTAL)')),
],
_('[-U] [-B] SOURCE [DEST]'),
norepo=True)
def share(ui, source, dest=None, noupdate=False, bookmarks=False,
relative=False):
"""create a new shared repository
Initialize a new repository and working directory that shares its
history (and optionally bookmarks) with another repository.
.. note::
using rollback or extensions that destroy/modify history (mq,
rebase, etc.) can cause considerable confusion with shared
clones. In particular, if two shared clones are both updated to
the same changeset, and one of them destroys that changeset
with rollback, the other clone will suddenly stop working: all
operations will fail with "abort: working directory has unknown
parent". The only known workaround is to use debugsetparents on
the broken clone to reset it to a changeset that still exists.
"""
hg.share(ui, source, dest=dest, update=not noupdate,
bookmarks=bookmarks, relative=relative)
return 0
@command('unshare', [], '')
def unshare(ui, repo):
"""convert a shared repository to a normal one
Copy the store data to the repo and remove the sharedpath data.
"""
if not repo.shared():
raise error.Abort(_("this is not a shared repo"))
hg.unshare(ui, repo)
# Wrap clone command to pass auto share options.
def clone(orig, ui, source, *args, **opts):
pool = ui.config('share', 'pool')
if pool:
pool = util.expandpath(pool)
opts[r'shareopts'] = {
'pool': pool,
'mode': ui.config('share', 'poolnaming'),
}
return orig(ui, source, *args, **opts)
def extsetup(ui):
extensions.wrapfunction(bookmarks, '_getbkfile', getbkfile)
extensions.wrapfunction(bookmarks.bmstore, '_recordchange', recordchange)
extensions.wrapfunction(bookmarks.bmstore, '_writerepo', writerepo)
extensions.wrapcommand(commands.table, 'clone', clone)
def _hassharedbookmarks(repo):
"""Returns whether this repo has shared bookmarks"""
try:
shared = repo.vfs.read('shared').splitlines()
except IOError as inst:
if inst.errno != errno.ENOENT:
raise
return False
return hg.sharedbookmarks in shared
def getbkfile(orig, repo):
if _hassharedbookmarks(repo):
srcrepo = hg.sharedreposource(repo)
if srcrepo is not None:
# just orig(srcrepo) doesn't work as expected, because
# HG_PENDING refers repo.root.
try:
fp, pending = txnutil.trypending(repo.root, repo.vfs,
'bookmarks')
if pending:
# only in this case, bookmark information in repo
# is up-to-date.
return fp
fp.close()
except IOError as inst:
if inst.errno != errno.ENOENT:
raise
# otherwise, we should read bookmarks from srcrepo,
# because .hg/bookmarks in srcrepo might be already
# changed via another sharing repo
repo = srcrepo
# TODO: Pending changes in repo are still invisible in
# srcrepo, because bookmarks.pending is written only into repo.
# See also https://www.mercurial-scm.org/wiki/SharedRepository
return orig(repo)
def recordchange(orig, self, tr):
# Continue with write to local bookmarks file as usual
orig(self, tr)
if _hassharedbookmarks(self._repo):
srcrepo = hg.sharedreposource(self._repo)
if srcrepo is not None:
category = 'share-bookmarks'
tr.addpostclose(category, lambda tr: self._writerepo(srcrepo))
def writerepo(orig, self, repo):
# First write local bookmarks file in case we ever unshare
orig(self, repo)
if _hassharedbookmarks(self._repo):
srcrepo = hg.sharedreposource(self._repo)
if srcrepo is not None:
orig(self, srcrepo)