Mercurial > hg
view mercurial/httppeer.py @ 26623:5a95fe44121d
clonebundles: support for seeding clones from pre-generated bundles
Cloning can be an expensive operation for servers because the server
generates a bundle from existing repository data at request time. For
a large repository like mozilla-central, this consumes 4+ minutes
of CPU time on the server. It also results in significant network
utilization. Multiplied by hundreds or even thousands of clients and
the ensuing load can result in difficulties scaling the Mercurial server.
Despite generation of bundles being deterministic until the next
changeset is added, the generation of bundles to service a clone request
is not cached. Each clone thus performs redundant work. This is
wasteful.
This patch introduces the "clonebundles" extension and related
client-side functionality to help alleviate this deficiency. The
client-side feature is behind an experimental flag and is not enabled by
default.
It works as follows:
1) Server operator generates a bundle and makes it available on a
server (likely HTTP).
2) Server operator defines the URL of a bundle file in a
.hg/clonebundles.manifest file.
3) Client `hg clone`ing sees the server is advertising bundle URLs.
4) Client fetches and applies the advertised bundle.
5) Client performs equivalent of `hg pull` to fetch changes made since
the bundle was created.
Essentially, the server performs the expensive work of generating a
bundle once and all subsequent clones fetch a static file from
somewhere. Scaling static file serving is a much more manageable
problem than scaling a Python application like Mercurial. Assuming your
repository grows less than 1% per day, the end result is 99+% of CPU
and network load from clones is eliminated, allowing Mercurial servers
to scale more easily. Serving static files also means data can be
transferred to clients as fast as they can consume it, rather than as
fast as servers can generate it. This makes clones faster.
Mozilla has implemented similar functionality of this patch on
hg.mozilla.org using a custom extension. We are hosting bundle files in
Amazon S3 and CloudFront (a CDN) and have successfully offloaded
>1 TB/day in data transfer from hg.mozilla.org, freeing up significant
bandwidth and CPU resources. The positive impact has been stellar and
I believe it has proved its value to be included in Mercurial core. I
feel it is important for the client-side support to be enabled in core
by default because it means that clients will get faster, more reliable
clones and will enable server operators to reduce load without
requiring any client-side configuration changes (assuming clients are
up to date, of course).
The scope of this feature is narrowly and specifically tailored to
cloning, despite "serve pulls from pre-generated bundles" being a valid
and useful feature. I would eventually like for Mercurial servers to
support transferring *all* repository data via statically hosted files.
You could imagine a server that siphons all pushed data to bundle files
and instructs clients to apply a stream of bundles to reconstruct all
repository data. This feature, while useful and powerful, is
significantly more work to implement because it requires the server
component have awareness of discovery and a mapping of which changesets
are in which files. Full, clone bundles, by contrast, are much simpler.
The wire protocol command is named "clonebundles" instead of something
more generic like "staticbundles" to leave the door open for a new, more
powerful and more generic server-side component with minimal backwards
compatibility implications. The name "bundleclone" is used by Mozilla's
extension and would cause problems since there are subtle differences
in Mozilla's extension.
Mozilla's experience with this idea has taught us that some form of
"content negotiation" is required. Not all clients will support all
bundle formats or even URLs (advanced TLS requirements, etc). To ensure
the highest uptake possible, a server needs to advertise multiple
versions of bundles and clients need to be able to choose the most
appropriate from that list one. The "attributes" in each
server-advertised entry facilitate this filtering and sorting. Their
use will become apparent in subsequent patches.
Initial inspiration and credit for the idea of cloning from static files
belongs to Augie Fackler and his "lookaside clone" extension proof of
concept.
author | Gregory Szorc <gregory.szorc@gmail.com> |
---|---|
date | Fri, 09 Oct 2015 11:22:01 -0700 |
parents | 56b2bcea2529 |
children | b502138f5faa |
line wrap: on
line source
# httppeer.py - HTTP repository proxy classes for mercurial # # Copyright 2005, 2006 Matt Mackall <mpm@selenic.com> # Copyright 2006 Vadim Gelfer <vadim.gelfer@gmail.com> # # 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 errno import httplib import os import socket import tempfile import urllib import urllib2 import zlib from .i18n import _ from .node import nullid from . import ( changegroup, error, httpconnection, statichttprepo, url, util, wireproto, ) def zgenerator(f): zd = zlib.decompressobj() try: for chunk in util.filechunkiter(f): while chunk: yield zd.decompress(chunk, 2**18) chunk = zd.unconsumed_tail except httplib.HTTPException: raise IOError(None, _('connection ended unexpectedly')) yield zd.flush() class httppeer(wireproto.wirepeer): def __init__(self, ui, path): self.path = path self.caps = None self.handler = None self.urlopener = None self.requestbuilder = None u = util.url(path) if u.query or u.fragment: raise error.Abort(_('unsupported URL component: "%s"') % (u.query or u.fragment)) # urllib cannot handle URLs with embedded user or passwd self._url, authinfo = u.authinfo() self.ui = ui self.ui.debug('using %s\n' % self._url) self.urlopener = url.opener(ui, authinfo) self.requestbuilder = urllib2.Request def __del__(self): if self.urlopener: for h in self.urlopener.handlers: h.close() getattr(h, "close_all", lambda : None)() def url(self): return self.path # look up capabilities only when needed def _fetchcaps(self): self.caps = set(self._call('capabilities').split()) def _capabilities(self): if self.caps is None: try: self._fetchcaps() except error.RepoError: self.caps = set() self.ui.debug('capabilities: %s\n' % (' '.join(self.caps or ['none']))) return self.caps def lock(self): raise error.Abort(_('operation not supported over http')) def _callstream(self, cmd, **args): if cmd == 'pushkey': args['data'] = '' data = args.pop('data', None) size = 0 if util.safehasattr(data, 'length'): size = data.length elif data is not None: size = len(data) headers = args.pop('headers', {}) if data is not None and 'Content-Type' not in headers: headers['Content-Type'] = 'application/mercurial-0.1' if size and self.ui.configbool('ui', 'usehttp2', False): headers['Expect'] = '100-Continue' headers['X-HgHttp2'] = '1' self.ui.debug("sending %s command\n" % cmd) q = [('cmd', cmd)] headersize = 0 if len(args) > 0: httpheader = self.capable('httpheader') if httpheader: headersize = int(httpheader.split(',')[0]) if headersize > 0: # The headers can typically carry more data than the URL. encargs = urllib.urlencode(sorted(args.items())) headerfmt = 'X-HgArg-%s' contentlen = headersize - len(headerfmt % '000' + ': \r\n') headernum = 0 for i in xrange(0, len(encargs), contentlen): headernum += 1 header = headerfmt % str(headernum) headers[header] = encargs[i:i + contentlen] varyheaders = [headerfmt % str(h) for h in range(1, headernum + 1)] headers['Vary'] = ','.join(varyheaders) else: q += sorted(args.items()) qs = '?%s' % urllib.urlencode(q) cu = "%s%s" % (self._url, qs) req = self.requestbuilder(cu, data, headers) if data is not None: self.ui.debug("sending %s bytes\n" % size) req.add_unredirected_header('Content-Length', '%d' % size) try: resp = self.urlopener.open(req) except urllib2.HTTPError as inst: if inst.code == 401: raise error.Abort(_('authorization failed')) raise except httplib.HTTPException as inst: self.ui.debug('http error while sending %s command\n' % cmd) self.ui.traceback() raise IOError(None, inst) except IndexError: # this only happens with Python 2.3, later versions raise URLError raise error.Abort(_('http error, possibly caused by proxy setting')) # record the url we got redirected to resp_url = resp.geturl() if resp_url.endswith(qs): resp_url = resp_url[:-len(qs)] if self._url.rstrip('/') != resp_url.rstrip('/'): if not self.ui.quiet: self.ui.warn(_('real URL is %s\n') % resp_url) self._url = resp_url try: proto = resp.getheader('content-type') except AttributeError: proto = resp.headers.get('content-type', '') safeurl = util.hidepassword(self._url) if proto.startswith('application/hg-error'): raise error.OutOfBandError(resp.read()) # accept old "text/plain" and "application/hg-changegroup" for now if not (proto.startswith('application/mercurial-') or (proto.startswith('text/plain') and not resp.headers.get('content-length')) or proto.startswith('application/hg-changegroup')): self.ui.debug("requested URL: '%s'\n" % util.hidepassword(cu)) raise error.RepoError( _("'%s' does not appear to be an hg repository:\n" "---%%<--- (%s)\n%s\n---%%<---\n") % (safeurl, proto or 'no content-type', resp.read(1024))) if proto.startswith('application/mercurial-'): try: version = proto.split('-', 1)[1] version_info = tuple([int(n) for n in version.split('.')]) except ValueError: raise error.RepoError(_("'%s' sent a broken Content-Type " "header (%s)") % (safeurl, proto)) if version_info > (0, 1): raise error.RepoError(_("'%s' uses newer protocol %s") % (safeurl, version)) return resp def _call(self, cmd, **args): fp = self._callstream(cmd, **args) try: return fp.read() finally: # if using keepalive, allow connection to be reused fp.close() def _callpush(self, cmd, cg, **args): # have to stream bundle to a temp file because we do not have # http 1.1 chunked transfer. types = self.capable('unbundle') try: types = types.split(',') except AttributeError: # servers older than d1b16a746db6 will send 'unbundle' as a # boolean capability. They only support headerless/uncompressed # bundles. types = [""] for x in types: if x in changegroup.bundletypes: type = x break tempname = changegroup.writebundle(self.ui, cg, None, type) fp = httpconnection.httpsendfile(self.ui, tempname, "rb") headers = {'Content-Type': 'application/mercurial-0.1'} try: r = self._call(cmd, data=fp, headers=headers, **args) vals = r.split('\n', 1) if len(vals) < 2: raise error.ResponseError(_("unexpected response:"), r) return vals except socket.error as err: if err.args[0] in (errno.ECONNRESET, errno.EPIPE): raise error.Abort(_('push failed: %s') % err.args[1]) raise error.Abort(err.args[1]) finally: fp.close() os.unlink(tempname) def _calltwowaystream(self, cmd, fp, **args): fh = None fp_ = None filename = None try: # dump bundle to disk fd, filename = tempfile.mkstemp(prefix="hg-bundle-", suffix=".hg") fh = os.fdopen(fd, "wb") d = fp.read(4096) while d: fh.write(d) d = fp.read(4096) fh.close() # start http push fp_ = httpconnection.httpsendfile(self.ui, filename, "rb") headers = {'Content-Type': 'application/mercurial-0.1'} return self._callstream(cmd, data=fp_, headers=headers, **args) finally: if fp_ is not None: fp_.close() if fh is not None: fh.close() os.unlink(filename) def _callcompressable(self, cmd, **args): stream = self._callstream(cmd, **args) return util.chunkbuffer(zgenerator(stream)) def _abort(self, exception): raise exception class httpspeer(httppeer): def __init__(self, ui, path): if not url.has_https: raise error.Abort(_('Python support for SSL and HTTPS ' 'is not installed')) httppeer.__init__(self, ui, path) def instance(ui, path, create): if create: raise error.Abort(_('cannot create new http repository')) try: if path.startswith('https:'): inst = httpspeer(ui, path) else: inst = httppeer(ui, path) try: # Try to do useful work when checking compatibility. # Usually saves a roundtrip since we want the caps anyway. inst._fetchcaps() except error.RepoError: # No luck, try older compatibility check. inst.between([(nullid, nullid)]) return inst except error.RepoError as httpexception: try: r = statichttprepo.instance(ui, "static-" + path, create) ui.note('(falling back to static-http)\n') return r except error.RepoError: raise httpexception # use the original http RepoError instead