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util: implement zstd compression engine...
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.

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hgclient.py
123 lines | 3.3 KiB | text/x-python | PythonLexer
Yuya Nishihara
test-commandserver: split helper functions to new hgclient module...
r22566 # A minimal client for Mercurial's command server
Pulkit Goyal
hgclient: use absolute_import and print_function
r28355 from __future__ import absolute_import, print_function
import os
import signal
import socket
import struct
import subprocess
import sys
import time
Yuya Nishihara
test-commandserver: split helper functions to new hgclient module...
r22566
timeless
test-commandserver: handle cStringIO.StringIO/io.StringIO divergence
r28836 try:
import cStringIO as io
stringio = io.StringIO
except ImportError:
import io
stringio = io.StringIO
Yuya Nishihara
test-commandserver: allow check() to make connection in different way...
r22992 def connectpipe(path=None):
Yuya Nishihara
test-commandserver: split helper functions to new hgclient module...
r22566 cmdline = ['hg', 'serve', '--cmdserver', 'pipe']
if path:
cmdline += ['-R', path]
server = subprocess.Popen(cmdline, stdin=subprocess.PIPE,
stdout=subprocess.PIPE)
return server
Yuya Nishihara
test-commandserver: add connector for unix domain socket server...
r22993 class unixconnection(object):
def __init__(self, sockpath):
self.sock = sock = socket.socket(socket.AF_UNIX)
sock.connect(sockpath)
self.stdin = sock.makefile('wb')
self.stdout = sock.makefile('rb')
def wait(self):
self.stdin.close()
self.stdout.close()
self.sock.close()
class unixserver(object):
def __init__(self, sockpath, logpath=None, repopath=None):
self.sockpath = sockpath
cmdline = ['hg', 'serve', '--cmdserver', 'unix', '-a', sockpath]
if repopath:
cmdline += ['-R', repopath]
if logpath:
stdout = open(logpath, 'a')
stderr = subprocess.STDOUT
else:
stdout = stderr = None
self.server = subprocess.Popen(cmdline, stdout=stdout, stderr=stderr)
# wait for listen()
while self.server.poll() is None:
if os.path.exists(sockpath):
break
time.sleep(0.1)
def connect(self):
return unixconnection(self.sockpath)
def shutdown(self):
os.kill(self.server.pid, signal.SIGTERM)
self.server.wait()
Yuya Nishihara
test-commandserver: split helper functions to new hgclient module...
r22566 def writeblock(server, data):
server.stdin.write(struct.pack('>I', len(data)))
server.stdin.write(data)
server.stdin.flush()
def readchannel(server):
data = server.stdout.read(5)
if not data:
raise EOFError
channel, length = struct.unpack('>cI', data)
if channel in 'IL':
return channel, length
else:
return channel, server.stdout.read(length)
def sep(text):
return text.replace('\\', '/')
def runcommand(server, args, output=sys.stdout, error=sys.stderr, input=None,
outfilter=lambda x: x):
Pulkit Goyal
hgclient: use absolute_import and print_function
r28355 print('*** runcommand', ' '.join(args))
Yuya Nishihara
test-commandserver: split helper functions to new hgclient module...
r22566 sys.stdout.flush()
server.stdin.write('runcommand\n')
writeblock(server, '\0'.join(args))
if not input:
timeless
test-commandserver: handle cStringIO.StringIO/io.StringIO divergence
r28836 input = stringio()
Yuya Nishihara
test-commandserver: split helper functions to new hgclient module...
r22566
while True:
ch, data = readchannel(server)
if ch == 'o':
output.write(outfilter(data))
output.flush()
elif ch == 'e':
error.write(data)
error.flush()
elif ch == 'I':
writeblock(server, input.read(data))
elif ch == 'L':
writeblock(server, input.readline(data))
elif ch == 'r':
ret, = struct.unpack('>i', data)
if ret != 0:
Pulkit Goyal
hgclient: use absolute_import and print_function
r28355 print(' [%d]' % ret)
Yuya Nishihara
test-commandserver: split helper functions to new hgclient module...
r22566 return ret
else:
Pulkit Goyal
hgclient: use absolute_import and print_function
r28355 print("unexpected channel %c: %r" % (ch, data))
Yuya Nishihara
test-commandserver: split helper functions to new hgclient module...
r22566 if ch.isupper():
return
Yuya Nishihara
test-commandserver: allow check() to make connection in different way...
r22992 def check(func, connect=connectpipe):
Yuya Nishihara
test-commandserver: split helper functions to new hgclient module...
r22566 sys.stdout.flush()
Yuya Nishihara
test-commandserver: remove unused repopath argument from check()...
r22991 server = connect()
Yuya Nishihara
test-commandserver: split helper functions to new hgclient module...
r22566 try:
return func(server)
finally:
server.stdin.close()
server.wait()