Mercurial > hg
view mercurial/pure/bdiff.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.
author | Gregory Szorc <gregory.szorc@gmail.com> |
---|---|
date | Sun, 16 Oct 2016 13:35:23 -0700 |
parents | d24e03da24b5 |
children | 6d30699729dd |
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# bdiff.py - Python implementation of bdiff.c # # Copyright 2009 Matt Mackall <mpm@selenic.com> and others # # 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 array import difflib import re import struct from . import policy policynocffi = policy.policynocffi modulepolicy = policy.policy def splitnewlines(text): '''like str.splitlines, but only split on newlines.''' lines = [l + '\n' for l in text.split('\n')] if lines: if lines[-1] == '\n': lines.pop() else: lines[-1] = lines[-1][:-1] return lines def _normalizeblocks(a, b, blocks): prev = None r = [] for curr in blocks: if prev is None: prev = curr continue shift = 0 a1, b1, l1 = prev a1end = a1 + l1 b1end = b1 + l1 a2, b2, l2 = curr a2end = a2 + l2 b2end = b2 + l2 if a1end == a2: while (a1end + shift < a2end and a[a1end + shift] == b[b1end + shift]): shift += 1 elif b1end == b2: while (b1end + shift < b2end and a[a1end + shift] == b[b1end + shift]): shift += 1 r.append((a1, b1, l1 + shift)) prev = a2 + shift, b2 + shift, l2 - shift r.append(prev) return r def _tostring(c): if type(c) is array.array: # this copy overhead isn't ideal return c.tostring() return str(c) def bdiff(a, b): a = _tostring(a).splitlines(True) b = _tostring(b).splitlines(True) if not a: s = "".join(b) return s and (struct.pack(">lll", 0, 0, len(s)) + s) bin = [] p = [0] for i in a: p.append(p[-1] + len(i)) d = difflib.SequenceMatcher(None, a, b).get_matching_blocks() d = _normalizeblocks(a, b, d) la = 0 lb = 0 for am, bm, size in d: s = "".join(b[lb:bm]) if am > la or s: bin.append(struct.pack(">lll", p[la], p[am], len(s)) + s) la = am + size lb = bm + size return "".join(bin) def blocks(a, b): an = splitnewlines(a) bn = splitnewlines(b) d = difflib.SequenceMatcher(None, an, bn).get_matching_blocks() d = _normalizeblocks(an, bn, d) return [(i, i + n, j, j + n) for (i, j, n) in d] def fixws(text, allws): if allws: text = re.sub('[ \t\r]+', '', text) else: text = re.sub('[ \t\r]+', ' ', text) text = text.replace(' \n', '\n') return text if modulepolicy not in policynocffi: try: from _bdiff_cffi import ffi, lib except ImportError: if modulepolicy == 'cffi': # strict cffi import raise else: def blocks(sa, sb): a = ffi.new("struct bdiff_line**") b = ffi.new("struct bdiff_line**") ac = ffi.new("char[]", str(sa)) bc = ffi.new("char[]", str(sb)) l = ffi.new("struct bdiff_hunk*") try: an = lib.bdiff_splitlines(ac, len(sa), a) bn = lib.bdiff_splitlines(bc, len(sb), b) if not a[0] or not b[0]: raise MemoryError count = lib.bdiff_diff(a[0], an, b[0], bn, l) if count < 0: raise MemoryError rl = [None] * count h = l.next i = 0 while h: rl[i] = (h.a1, h.a2, h.b1, h.b2) h = h.next i += 1 finally: lib.free(a[0]) lib.free(b[0]) lib.bdiff_freehunks(l.next) return rl def bdiff(sa, sb): a = ffi.new("struct bdiff_line**") b = ffi.new("struct bdiff_line**") ac = ffi.new("char[]", str(sa)) bc = ffi.new("char[]", str(sb)) l = ffi.new("struct bdiff_hunk*") try: an = lib.bdiff_splitlines(ac, len(sa), a) bn = lib.bdiff_splitlines(bc, len(sb), b) if not a[0] or not b[0]: raise MemoryError count = lib.bdiff_diff(a[0], an, b[0], bn, l) if count < 0: raise MemoryError rl = [] h = l.next la = lb = 0 while h: if h.a1 != la or h.b1 != lb: lgt = (b[0] + h.b1).l - (b[0] + lb).l rl.append(struct.pack(">lll", (a[0] + la).l - a[0].l, (a[0] + h.a1).l - a[0].l, lgt)) rl.append(str(ffi.buffer((b[0] + lb).l, lgt))) la = h.a2 lb = h.b2 h = h.next finally: lib.free(a[0]) lib.free(b[0]) lib.bdiff_freehunks(l.next) return "".join(rl)