view mercurial/pycompat.py @ 30212:260af19891f2

changegroup: increase write buffer size to 128k

By default, Python defers to the operating system for choosing the
default buffer size on opened files. On my Linux machine, the default
is 4k, which is really small for 2016.

This patch bumps the write buffer size when writing
changegroups/bundles to 128k. This matches the 128k read buffer
we already use on revlogs.

It's worth noting that this only impacts when writing to an explicit
file (such as during `hg bundle`). Buffers when writing to bundle
files via the repo vfs or to a temporary file are not impacted.

When producing a none-v2 bundle file of the mozilla-unified repository,
this change caused the number of write() system calls to drop from
952,449 to 29,788. After this change, the most frequent system
calls are fstat(), read(), lseek(), and open(). There were
2,523,672 system calls after this patch (so a net decrease of
~950k is statistically significant).

This change shows no performance change on my system. But I have a
high-end system with a fast SSD. It is quite possible this change
will have a significant impact on network file systems, where
extra network round trips due to excessive I/O system calls could
introduce significant latency.

# pycompat.py - portability shim for python 3
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

"""Mercurial portability shim for python 3.

This contains aliases to hide python version-specific details from the core.
"""

from __future__ import absolute_import

import sys

ispy3 = (sys.version_info[0] >= 3)

if not ispy3:
    import cPickle as pickle
    import cStringIO as io
    import httplib
    import Queue as _queue
    import SocketServer as socketserver
    import urlparse
    import xmlrpclib
else:
    import http.client as httplib
    import io
    import pickle
    import queue as _queue
    import socketserver
    import urllib.parse as urlparse
    import xmlrpc.client as xmlrpclib

if ispy3:
    import builtins
    import functools
    import os
    fsencode = os.fsencode

    def sysstr(s):
        """Return a keyword str to be passed to Python functions such as
        getattr() and str.encode()

        This never raises UnicodeDecodeError. Non-ascii characters are
        considered invalid and mapped to arbitrary but unique code points
        such that 'sysstr(a) != sysstr(b)' for all 'a != b'.
        """
        if isinstance(s, builtins.str):
            return s
        return s.decode(u'latin-1')

    def _wrapattrfunc(f):
        @functools.wraps(f)
        def w(object, name, *args):
            return f(object, sysstr(name), *args)
        return w

    # these wrappers are automagically imported by hgloader
    delattr = _wrapattrfunc(builtins.delattr)
    getattr = _wrapattrfunc(builtins.getattr)
    hasattr = _wrapattrfunc(builtins.hasattr)
    setattr = _wrapattrfunc(builtins.setattr)
    xrange = builtins.range

else:
    def sysstr(s):
        return s

    # Partial backport from os.py in Python 3, which only accepts bytes.
    # In Python 2, our paths should only ever be bytes, a unicode path
    # indicates a bug.
    def fsencode(filename):
        if isinstance(filename, str):
            return filename
        else:
            raise TypeError(
                "expect str, not %s" % type(filename).__name__)

stringio = io.StringIO
empty = _queue.Empty
queue = _queue.Queue

class _pycompatstub(object):
    def __init__(self):
        self._aliases = {}

    def _registeraliases(self, origin, items):
        """Add items that will be populated at the first access"""
        items = map(sysstr, items)
        self._aliases.update(
            (item.replace(sysstr('_'), sysstr('')).lower(), (origin, item))
            for item in items)

    def __getattr__(self, name):
        try:
            origin, item = self._aliases[name]
        except KeyError:
            raise AttributeError(name)
        self.__dict__[name] = obj = getattr(origin, item)
        return obj

httpserver = _pycompatstub()
urlreq = _pycompatstub()
urlerr = _pycompatstub()
if not ispy3:
    import BaseHTTPServer
    import CGIHTTPServer
    import SimpleHTTPServer
    import urllib2
    import urllib
    urlreq._registeraliases(urllib, (
        "addclosehook",
        "addinfourl",
        "ftpwrapper",
        "pathname2url",
        "quote",
        "splitattr",
        "splitpasswd",
        "splitport",
        "splituser",
        "unquote",
        "url2pathname",
        "urlencode",
    ))
    urlreq._registeraliases(urllib2, (
        "AbstractHTTPHandler",
        "BaseHandler",
        "build_opener",
        "FileHandler",
        "FTPHandler",
        "HTTPBasicAuthHandler",
        "HTTPDigestAuthHandler",
        "HTTPHandler",
        "HTTPPasswordMgrWithDefaultRealm",
        "HTTPSHandler",
        "install_opener",
        "ProxyHandler",
        "Request",
        "urlopen",
    ))
    urlerr._registeraliases(urllib2, (
        "HTTPError",
        "URLError",
    ))
    httpserver._registeraliases(BaseHTTPServer, (
        "HTTPServer",
        "BaseHTTPRequestHandler",
    ))
    httpserver._registeraliases(SimpleHTTPServer, (
        "SimpleHTTPRequestHandler",
    ))
    httpserver._registeraliases(CGIHTTPServer, (
        "CGIHTTPRequestHandler",
    ))

else:
    import urllib.request
    urlreq._registeraliases(urllib.request, (
        "AbstractHTTPHandler",
        "addclosehook",
        "addinfourl",
        "BaseHandler",
        "build_opener",
        "FileHandler",
        "FTPHandler",
        "ftpwrapper",
        "HTTPHandler",
        "HTTPSHandler",
        "install_opener",
        "pathname2url",
        "HTTPBasicAuthHandler",
        "HTTPDigestAuthHandler",
        "HTTPPasswordMgrWithDefaultRealm",
        "ProxyHandler",
        "quote",
        "Request",
        "splitattr",
        "splitpasswd",
        "splitport",
        "splituser",
        "unquote",
        "url2pathname",
        "urlopen",
    ))
    import urllib.error
    urlerr._registeraliases(urllib.error, (
        "HTTPError",
        "URLError",
    ))
    import http.server
    httpserver._registeraliases(http.server, (
        "HTTPServer",
        "BaseHTTPRequestHandler",
        "SimpleHTTPRequestHandler",
        "CGIHTTPRequestHandler",
    ))