view mercurial/hgweb/protocol.py @ 30451:41a8106789ca

util: implement zstd compression engine Now that zstd is vendored and being built (in some configurations), we can implement a compression engine for zstd! The zstd engine is a little different from existing engines. Because it may not always be present, we have to defer load the module in case importing it fails. We facilitate this via a cached property that holds a reference to the module or None. The "available" method is implemented to reflect reality. The zstd engine declares its ability to handle bundles using the "zstd" human name and the "ZS" internal name. The latter was chosen because internal names are 2 characters (by only convention I think) and "ZS" seems reasonable. The engine, like others, supports specifying the compression level. However, there are no consumers of this API that yet pass in that argument. I have plans to change that, so stay tuned. Since all we need to do to support bundle generation with a new compression engine is implement and register the compression engine, bundle generation with zstd "just works!" Tests demonstrating this have been added. How does performance of zstd for bundle generation compare? On the mozilla-unified repo, `hg bundle --all -t <engine>-v2` yields the following on my i7-6700K on Linux: engine CPU time bundle size vs orig size throughput none 97.0s 4,054,405,584 100.0% 41.8 MB/s bzip2 (l=9) 393.6s 975,343,098 24.0% 10.3 MB/s gzip (l=6) 184.0s 1,140,533,074 28.1% 22.0 MB/s zstd (l=1) 108.2s 1,119,434,718 27.6% 37.5 MB/s zstd (l=2) 111.3s 1,078,328,002 26.6% 36.4 MB/s zstd (l=3) 113.7s 1,011,823,727 25.0% 35.7 MB/s zstd (l=4) 116.0s 1,008,965,888 24.9% 35.0 MB/s zstd (l=5) 121.0s 977,203,148 24.1% 33.5 MB/s zstd (l=6) 131.7s 927,360,198 22.9% 30.8 MB/s zstd (l=7) 139.0s 912,808,505 22.5% 29.2 MB/s zstd (l=12) 198.1s 854,527,714 21.1% 20.5 MB/s zstd (l=18) 681.6s 789,750,690 19.5% 5.9 MB/s On compression, zstd for bundle generation delivers: * better compression than gzip with significantly less CPU utilization * better than bzip2 compression ratios while still being significantly faster than gzip * ability to aggressively tune compression level to achieve significantly smaller bundles That last point is important. With clone bundles, a server can pre-generate a bundle file, upload it to a static file server, and redirect clients to transparently download it during clone. The server could choose to produce a zstd bundle with the highest compression settings possible. This would take a very long time - a magnitude longer than a typical zstd bundle generation - but the result would be hundreds of megabytes smaller! For the clone volume we do at Mozilla, this could translate to petabytes of bandwidth savings per year and faster clones (due to smaller transfer size). I don't have detailed numbers to report on decompression. However, zstd decompression is fast: >1 GB/s output throughput on this machine, even through the Python bindings. And it can do that regardless of the compression level of the input. By the time you have enough data to worry about overhead of decompression, you have plenty of other things to worry about performance wise. zstd is wins all around. I can't wait to implement support for it on the wire protocol and in revlogs.
author Gregory Szorc <gregory.szorc@gmail.com>
date Fri, 11 Nov 2016 01:10:07 -0800
parents 038547a14d85
children 2add671bf55b
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#
# Copyright 21 May 2005 - (c) 2005 Jake Edge <jake@edge2.net>
# Copyright 2005-2007 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.

from __future__ import absolute_import

import cgi

from .common import (
    HTTP_OK,
)

from .. import (
    util,
    wireproto,
)
stringio = util.stringio

urlerr = util.urlerr
urlreq = util.urlreq

HGTYPE = 'application/mercurial-0.1'
HGERRTYPE = 'application/hg-error'

class webproto(wireproto.abstractserverproto):
    def __init__(self, req, ui):
        self.req = req
        self.response = ''
        self.ui = ui
    def getargs(self, args):
        knownargs = self._args()
        data = {}
        keys = args.split()
        for k in keys:
            if k == '*':
                star = {}
                for key in knownargs.keys():
                    if key != 'cmd' and key not in keys:
                        star[key] = knownargs[key][0]
                data['*'] = star
            else:
                data[k] = knownargs[k][0]
        return [data[k] for k in keys]
    def _args(self):
        args = self.req.form.copy()
        postlen = int(self.req.env.get('HTTP_X_HGARGS_POST', 0))
        if postlen:
            args.update(cgi.parse_qs(
                self.req.read(postlen), keep_blank_values=True))
            return args
        chunks = []
        i = 1
        while True:
            h = self.req.env.get('HTTP_X_HGARG_' + str(i))
            if h is None:
                break
            chunks += [h]
            i += 1
        args.update(cgi.parse_qs(''.join(chunks), keep_blank_values=True))
        return args
    def getfile(self, fp):
        length = int(self.req.env['CONTENT_LENGTH'])
        for s in util.filechunkiter(self.req, limit=length):
            fp.write(s)
    def redirect(self):
        self.oldio = self.ui.fout, self.ui.ferr
        self.ui.ferr = self.ui.fout = stringio()
    def restore(self):
        val = self.ui.fout.getvalue()
        self.ui.ferr, self.ui.fout = self.oldio
        return val

    def groupchunks(self, fh):
        def getchunks():
            while True:
                chunk = fh.read(32768)
                if not chunk:
                    break
                yield chunk

        return self.compresschunks(getchunks())

    def compresschunks(self, chunks):
        # Don't allow untrusted settings because disabling compression or
        # setting a very high compression level could lead to flooding
        # the server's network or CPU.
        opts = {'level': self.ui.configint('server', 'zliblevel', -1)}
        return util.compengines['zlib'].compressstream(chunks, opts)

    def _client(self):
        return 'remote:%s:%s:%s' % (
            self.req.env.get('wsgi.url_scheme') or 'http',
            urlreq.quote(self.req.env.get('REMOTE_HOST', '')),
            urlreq.quote(self.req.env.get('REMOTE_USER', '')))

def iscmd(cmd):
    return cmd in wireproto.commands

def call(repo, req, cmd):
    p = webproto(req, repo.ui)
    rsp = wireproto.dispatch(repo, p, cmd)
    if isinstance(rsp, str):
        req.respond(HTTP_OK, HGTYPE, body=rsp)
        return []
    elif isinstance(rsp, wireproto.streamres):
        req.respond(HTTP_OK, HGTYPE)
        return rsp.gen
    elif isinstance(rsp, wireproto.pushres):
        val = p.restore()
        rsp = '%d\n%s' % (rsp.res, val)
        req.respond(HTTP_OK, HGTYPE, body=rsp)
        return []
    elif isinstance(rsp, wireproto.pusherr):
        # drain the incoming bundle
        req.drain()
        p.restore()
        rsp = '0\n%s\n' % rsp.res
        req.respond(HTTP_OK, HGTYPE, body=rsp)
        return []
    elif isinstance(rsp, wireproto.ooberror):
        rsp = rsp.message
        req.respond(HTTP_OK, HGERRTYPE, body=rsp)
        return []