mercurial/changelog.py

revlog: add option to mmap revlog index

Following on from Jun Wu's patch last October[1], we have found that using mmap
for the revlog index in repos with large revlogs gives a noticable performance
improvment (~110ms on each hg invocation), particularly for commands that don't
touch the index very much.

This changeset adds this as an option, activated by a new experimental config
option so that it can be enabled on a per-repo basis. The configuration option
specifies an index size threshold at which Mercurial will switch to using mmap
to access the index.

If the configuration option is not specified, the default remains to load the
full file, which seems to be the best option for smaller repos.

Some initial performance numbers for average of 5 invocations of `hg log -l 5`
for different cache states:

| Repo: | HG | FB |
|---|---|---|
| Index size: | 2.3MB | much bigger |
| read (warm): | 237ms | 432ms |
| mmap (warm): | 227ms | 321ms |
|   | (-3%) | (-26%) |
| read (cold): | 397ms | 696ms |
| mmap (cold): | 410ms | 888ms |
|   | (+3%) | (+28%) |

[1] https://www.mercurial-scm.org/pipermail/mercurial-devel/2016-October/088737.html

Test Plan:
`hg log --config experimental.mmapindex=true`

Differential Revision: https://phab.mercurial-scm.org/D477

# changelog.py - changelog class for mercurial
#
# Copyright 2005-2007 Matt Mackall <[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.

from __future__ import absolute_import

import collections

from .i18n import _
from .node import (
    bin,
    hex,
    nullid,
)

from . import (
    encoding,
    error,
    revlog,
    util,
)

_defaultextra = {'branch': 'default'}

def _string_escape(text):
    """
    >>> from .pycompat import bytechr as chr
    >>> d = {b'nl': chr(10), b'bs': chr(92), b'cr': chr(13), b'nul': chr(0)}
    >>> s = b"ab%(nl)scd%(bs)s%(bs)sn%(nul)sab%(cr)scd%(bs)s%(nl)s" % d
    >>> s
    'ab\\ncd\\\\\\\\n\\x00ab\\rcd\\\\\\n'
    >>> res = _string_escape(s)
    >>> s == util.unescapestr(res)
    True
    """
    # subset of the string_escape codec
    text = text.replace('\\', '\\\\').replace('\n', '\\n').replace('\r', '\\r')
    return text.replace('\0', '\\0')

def decodeextra(text):
    """
    >>> from .pycompat import bytechr as chr
    >>> sorted(decodeextra(encodeextra({b'foo': b'bar', b'baz': chr(0) + b'2'})
    ...                    ).items())
    [('baz', '\\x002'), ('branch', 'default'), ('foo', 'bar')]
    >>> sorted(decodeextra(encodeextra({b'foo': b'bar',
    ...                                 b'baz': chr(92) + chr(0) + b'2'})
    ...                    ).items())
    [('baz', '\\\\\\x002'), ('branch', 'default'), ('foo', 'bar')]
    """
    extra = _defaultextra.copy()
    for l in text.split('\0'):
        if l:
            if '\\0' in l:
                # fix up \0 without getting into trouble with \\0
                l = l.replace('\\\\', '\\\\\n')
                l = l.replace('\\0', '\0')
                l = l.replace('\n', '')
            k, v = util.unescapestr(l).split(':', 1)
            extra[k] = v
    return extra

def encodeextra(d):
    # keys must be sorted to produce a deterministic changelog entry
    items = [_string_escape('%s:%s' % (k, d[k])) for k in sorted(d)]
    return "\0".join(items)

def stripdesc(desc):
    """strip trailing whitespace and leading and trailing empty lines"""
    return '\n'.join([l.rstrip() for l in desc.splitlines()]).strip('\n')

class appender(object):
    '''the changelog index must be updated last on disk, so we use this class
    to delay writes to it'''
    def __init__(self, vfs, name, mode, buf):
        self.data = buf
        fp = vfs(name, mode)
        self.fp = fp
        self.offset = fp.tell()
        self.size = vfs.fstat(fp).st_size
        self._end = self.size

    def end(self):
        return self._end
    def tell(self):
        return self.offset
    def flush(self):
        pass
    def close(self):
        self.fp.close()

    def seek(self, offset, whence=0):
        '''virtual file offset spans real file and data'''
        if whence == 0:
            self.offset = offset
        elif whence == 1:
            self.offset += offset
        elif whence == 2:
            self.offset = self.end() + offset
        if self.offset < self.size:
            self.fp.seek(self.offset)

    def read(self, count=-1):
        '''only trick here is reads that span real file and data'''
        ret = ""
        if self.offset < self.size:
            s = self.fp.read(count)
            ret = s
            self.offset += len(s)
            if count > 0:
                count -= len(s)
        if count != 0:
            doff = self.offset - self.size
            self.data.insert(0, "".join(self.data))
            del self.data[1:]
            s = self.data[0][doff:doff + count]
            self.offset += len(s)
            ret += s
        return ret

    def write(self, s):
        self.data.append(bytes(s))
        self.offset += len(s)
        self._end += len(s)

def _divertopener(opener, target):
    """build an opener that writes in 'target.a' instead of 'target'"""
    def _divert(name, mode='r', checkambig=False):
        if name != target:
            return opener(name, mode)
        return opener(name + ".a", mode)
    return _divert

def _delayopener(opener, target, buf):
    """build an opener that stores chunks in 'buf' instead of 'target'"""
    def _delay(name, mode='r', checkambig=False):
        if name != target:
            return opener(name, mode)
        return appender(opener, name, mode, buf)
    return _delay

_changelogrevision = collections.namedtuple(u'changelogrevision',
                                            (u'manifest', u'user', u'date',
                                             u'files', u'description',
                                             u'extra'))

class changelogrevision(object):
    """Holds results of a parsed changelog revision.

    Changelog revisions consist of multiple pieces of data, including
    the manifest node, user, and date. This object exposes a view into
    the parsed object.
    """

    __slots__ = (
        u'_offsets',
        u'_text',
    )

    def __new__(cls, text):
        if not text:
            return _changelogrevision(
                manifest=nullid,
                user='',
                date=(0, 0),
                files=[],
                description='',
                extra=_defaultextra,
            )

        self = super(changelogrevision, cls).__new__(cls)
        # We could return here and implement the following as an __init__.
        # But doing it here is equivalent and saves an extra function call.

        # format used:
        # nodeid\n        : manifest node in ascii
        # user\n          : user, no \n or \r allowed
        # time tz extra\n : date (time is int or float, timezone is int)
        #                 : extra is metadata, encoded and separated by '\0'
        #                 : older versions ignore it
        # files\n\n       : files modified by the cset, no \n or \r allowed
        # (.*)            : comment (free text, ideally utf-8)
        #
        # changelog v0 doesn't use extra

        nl1 = text.index('\n')
        nl2 = text.index('\n', nl1 + 1)
        nl3 = text.index('\n', nl2 + 1)

        # The list of files may be empty. Which means nl3 is the first of the
        # double newline that precedes the description.
        if text[nl3 + 1:nl3 + 2] == '\n':
            doublenl = nl3
        else:
            doublenl = text.index('\n\n', nl3 + 1)

        self._offsets = (nl1, nl2, nl3, doublenl)
        self._text = text

        return self

    @property
    def manifest(self):
        return bin(self._text[0:self._offsets[0]])

    @property
    def user(self):
        off = self._offsets
        return encoding.tolocal(self._text[off[0] + 1:off[1]])

    @property
    def _rawdate(self):
        off = self._offsets
        dateextra = self._text[off[1] + 1:off[2]]
        return dateextra.split(' ', 2)[0:2]

    @property
    def _rawextra(self):
        off = self._offsets
        dateextra = self._text[off[1] + 1:off[2]]
        fields = dateextra.split(' ', 2)
        if len(fields) != 3:
            return None

        return fields[2]

    @property
    def date(self):
        raw = self._rawdate
        time = float(raw[0])
        # Various tools did silly things with the timezone.
        try:
            timezone = int(raw[1])
        except ValueError:
            timezone = 0

        return time, timezone

    @property
    def extra(self):
        raw = self._rawextra
        if raw is None:
            return _defaultextra

        return decodeextra(raw)

    @property
    def files(self):
        off = self._offsets
        if off[2] == off[3]:
            return []

        return self._text[off[2] + 1:off[3]].split('\n')

    @property
    def description(self):
        return encoding.tolocal(self._text[self._offsets[3] + 2:])

class changelog(revlog.revlog):
    def __init__(self, opener, trypending=False):
        """Load a changelog revlog using an opener.

        If ``trypending`` is true, we attempt to load the index from a
        ``00changelog.i.a`` file instead of the default ``00changelog.i``.
        The ``00changelog.i.a`` file contains index (and possibly inline
        revision) data for a transaction that hasn't been finalized yet.
        It exists in a separate file to facilitate readers (such as
        hooks processes) accessing data before a transaction is finalized.
        """
        if trypending and opener.exists('00changelog.i.a'):
            indexfile = '00changelog.i.a'
        else:
            indexfile = '00changelog.i'

        datafile = '00changelog.d'
        revlog.revlog.__init__(self, opener, indexfile, datafile=datafile,
                               checkambig=True, mmaplargeindex=True)

        if self._initempty:
            # changelogs don't benefit from generaldelta
            self.version &= ~revlog.FLAG_GENERALDELTA
            self._generaldelta = False

        # Delta chains for changelogs tend to be very small because entries
        # tend to be small and don't delta well with each. So disable delta
        # chains.
        self.storedeltachains = False

        self._realopener = opener
        self._delayed = False
        self._delaybuf = None
        self._divert = False
        self.filteredrevs = frozenset()

    def tip(self):
        """filtered version of revlog.tip"""
        for i in xrange(len(self) -1, -2, -1):
            if i not in self.filteredrevs:
                return self.node(i)

    def __contains__(self, rev):
        """filtered version of revlog.__contains__"""
        return (0 <= rev < len(self)
                and rev not in self.filteredrevs)

    def __iter__(self):
        """filtered version of revlog.__iter__"""
        if len(self.filteredrevs) == 0:
            return revlog.revlog.__iter__(self)

        def filterediter():
            for i in xrange(len(self)):
                if i not in self.filteredrevs:
                    yield i

        return filterediter()

    def revs(self, start=0, stop=None):
        """filtered version of revlog.revs"""
        for i in super(changelog, self).revs(start, stop):
            if i not in self.filteredrevs:
                yield i

    @util.propertycache
    def nodemap(self):
        # XXX need filtering too
        self.rev(self.node(0))
        return self._nodecache

    def reachableroots(self, minroot, heads, roots, includepath=False):
        return self.index.reachableroots2(minroot, heads, roots, includepath)

    def headrevs(self):
        if self.filteredrevs:
            try:
                return self.index.headrevsfiltered(self.filteredrevs)
            # AttributeError covers non-c-extension environments and
            # old c extensions without filter handling.
            except AttributeError:
                return self._headrevs()

        return super(changelog, self).headrevs()

    def strip(self, *args, **kwargs):
        # XXX make something better than assert
        # We can't expect proper strip behavior if we are filtered.
        assert not self.filteredrevs
        super(changelog, self).strip(*args, **kwargs)

    def rev(self, node):
        """filtered version of revlog.rev"""
        r = super(changelog, self).rev(node)
        if r in self.filteredrevs:
            raise error.FilteredLookupError(hex(node), self.indexfile,
                                            _('filtered node'))
        return r

    def node(self, rev):
        """filtered version of revlog.node"""
        if rev in self.filteredrevs:
            raise error.FilteredIndexError(rev)
        return super(changelog, self).node(rev)

    def linkrev(self, rev):
        """filtered version of revlog.linkrev"""
        if rev in self.filteredrevs:
            raise error.FilteredIndexError(rev)
        return super(changelog, self).linkrev(rev)

    def parentrevs(self, rev):
        """filtered version of revlog.parentrevs"""
        if rev in self.filteredrevs:
            raise error.FilteredIndexError(rev)
        return super(changelog, self).parentrevs(rev)

    def flags(self, rev):
        """filtered version of revlog.flags"""
        if rev in self.filteredrevs:
            raise error.FilteredIndexError(rev)
        return super(changelog, self).flags(rev)

    def delayupdate(self, tr):
        "delay visibility of index updates to other readers"

        if not self._delayed:
            if len(self) == 0:
                self._divert = True
                if self._realopener.exists(self.indexfile + '.a'):
                    self._realopener.unlink(self.indexfile + '.a')
                self.opener = _divertopener(self._realopener, self.indexfile)
            else:
                self._delaybuf = []
                self.opener = _delayopener(self._realopener, self.indexfile,
                                           self._delaybuf)
        self._delayed = True
        tr.addpending('cl-%i' % id(self), self._writepending)
        tr.addfinalize('cl-%i' % id(self), self._finalize)

    def _finalize(self, tr):
        "finalize index updates"
        self._delayed = False
        self.opener = self._realopener
        # move redirected index data back into place
        if self._divert:
            assert not self._delaybuf
            tmpname = self.indexfile + ".a"
            nfile = self.opener.open(tmpname)
            nfile.close()
            self.opener.rename(tmpname, self.indexfile, checkambig=True)
        elif self._delaybuf:
            fp = self.opener(self.indexfile, 'a', checkambig=True)
            fp.write("".join(self._delaybuf))
            fp.close()
            self._delaybuf = None
        self._divert = False
        # split when we're done
        self.checkinlinesize(tr)

    def _writepending(self, tr):
        "create a file containing the unfinalized state for pretxnchangegroup"
        if self._delaybuf:
            # make a temporary copy of the index
            fp1 = self._realopener(self.indexfile)
            pendingfilename = self.indexfile + ".a"
            # register as a temp file to ensure cleanup on failure
            tr.registertmp(pendingfilename)
            # write existing data
            fp2 = self._realopener(pendingfilename, "w")
            fp2.write(fp1.read())
            # add pending data
            fp2.write("".join(self._delaybuf))
            fp2.close()
            # switch modes so finalize can simply rename
            self._delaybuf = None
            self._divert = True
            self.opener = _divertopener(self._realopener, self.indexfile)

        if self._divert:
            return True

        return False

    def checkinlinesize(self, tr, fp=None):
        if not self._delayed:
            revlog.revlog.checkinlinesize(self, tr, fp)

    def read(self, node):
        """Obtain data from a parsed changelog revision.

        Returns a 6-tuple of:

           - manifest node in binary
           - author/user as a localstr
           - date as a 2-tuple of (time, timezone)
           - list of files
           - commit message as a localstr
           - dict of extra metadata

        Unless you need to access all fields, consider calling
        ``changelogrevision`` instead, as it is faster for partial object
        access.
        """
        c = changelogrevision(self.revision(node))
        return (
            c.manifest,
            c.user,
            c.date,
            c.files,
            c.description,
            c.extra
        )

    def changelogrevision(self, nodeorrev):
        """Obtain a ``changelogrevision`` for a node or revision."""
        return changelogrevision(self.revision(nodeorrev))

    def readfiles(self, node):
        """
        short version of read that only returns the files modified by the cset
        """
        text = self.revision(node)
        if not text:
            return []
        last = text.index("\n\n")
        l = text[:last].split('\n')
        return l[3:]

    def add(self, manifest, files, desc, transaction, p1, p2,
                  user, date=None, extra=None):
        # Convert to UTF-8 encoded bytestrings as the very first
        # thing: calling any method on a localstr object will turn it
        # into a str object and the cached UTF-8 string is thus lost.
        user, desc = encoding.fromlocal(user), encoding.fromlocal(desc)

        user = user.strip()
        # An empty username or a username with a "\n" will make the
        # revision text contain two "\n\n" sequences -> corrupt
        # repository since read cannot unpack the revision.
        if not user:
            raise error.RevlogError(_("empty username"))
        if "\n" in user:
            raise error.RevlogError(_("username %s contains a newline")
                                    % repr(user))

        desc = stripdesc(desc)

        if date:
            parseddate = "%d %d" % util.parsedate(date)
        else:
            parseddate = "%d %d" % util.makedate()
        if extra:
            branch = extra.get("branch")
            if branch in ("default", ""):
                del extra["branch"]
            elif branch in (".", "null", "tip"):
                raise error.RevlogError(_('the name \'%s\' is reserved')
                                        % branch)
        if extra:
            extra = encodeextra(extra)
            parseddate = "%s %s" % (parseddate, extra)
        l = [hex(manifest), user, parseddate] + sorted(files) + ["", desc]
        text = "\n".join(l)
        return self.addrevision(text, transaction, len(self), p1, p2)

    def branchinfo(self, rev):
        """return the branch name and open/close state of a revision

        This function exists because creating a changectx object
        just to access this is costly."""
        extra = self.read(rev)[5]
        return encoding.tolocal(extra.get("branch")), 'close' in extra

    def _addrevision(self, node, rawtext, transaction, *args, **kwargs):
        # overlay over the standard revlog._addrevision to track the new
        # revision on the transaction.
        rev = len(self)
        node = super(changelog, self)._addrevision(node, rawtext, transaction,
                                                   *args, **kwargs)
        revs = transaction.changes.get('revs')
        if revs is not None:
            revs.add(rev)
        return node