upstream/mercurial-mirror Files · mercurial/diffhelper.py

snapshot: search for unrelated but reusable full-snapshot...

snapshot: search for unrelated but reusable full-snapshot # New Strategy Step: Reusing Snapshot Outside Of Parents' Chain. If no suitable bases were found in the parent's chains, see if we could reuse a full snapshot not directly related to the current revision. Such search can be expensive, so we only search for snapshots appended to the revlog *after* the bases used by the parents of the current revision (the one we just tested). We assume the parent's bases were created because the previous snapshots were unsuitable, so there are low odds they would be useful now. This search gives a chance to reuse a delta chain unrelated to the current revision. Without this re-use, topological branches would keep reopening new full chains. Creating more and more snapshots as the repository grow. In repositories with many topological branches, the lack of delta reuse can create too many snapshots reducing overall compression to nothing. This results in a very large repository and other usability issues. For now, we still focus on creating level-1 snapshots. However, this principle will play a large part in how we avoid snapshot explosion once we have more snapshot levels. # Effects On The Test Repository In the test repository we created, we can see the beneficial effect of such reuse. We need very few level-0 snapshots and the overall revlog size has decreased. The `hg debugrevlog` call, show a "lvl-2" snapshot. It comes from the existing delta logic using the `prev` revision (revlog's tip) as the base. In this specific case, it turns out the tip was a level-1 snapshot. This is a coincidence that can be ignored. Finding and testing against all these unrelated snapshots can have a performance impact at write time. We currently focus on building good deltas chain we build. Performance concern will be dealt with later in another series.

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      # diffhelper.py - helper routines for patch

      #

      # 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

      from .i18n import _

      from . import (

          error,

          pycompat,

      )

      def addlines(fp, hunk, lena, lenb, a, b):

          """Read lines from fp into the hunk

          The hunk is parsed into two arrays, a and b. a gets the old state of

          the text, b gets the new state. The control char from the hunk is saved

          when inserting into a, but not b (for performance while deleting files.)

          """

          while True:

              todoa = lena - len(a)

              todob = lenb - len(b)

              num = max(todoa, todob)

              if num == 0:

                  break

              for i in pycompat.xrange(num):

                  s = fp.readline()

                  if not s:

                      raise error.ParseError(_('incomplete hunk'))

                  if s == "\\ No newline at end of file\n":

                      fixnewline(hunk, a, b)

                      continue

                  if s == '\n' or s == '\r\n':

                      # Some patches may be missing the control char

                      # on empty lines. Supply a leading space.

                      s = ' ' + s

                  hunk.append(s)

                  if s.startswith('+'):

                      b.append(s[1:])

                  elif s.startswith('-'):

                      a.append(s)

                  else:

                      b.append(s[1:])

                      a.append(s)

      def fixnewline(hunk, a, b):

          """Fix up the last lines of a and b when the patch has no newline at EOF"""

          l = hunk[-1]

          # tolerate CRLF in last line

          if l.endswith('\r\n'):

              hline = l[:-2]

          else:

              hline = l[:-1]

          if hline.startswith((' ', '+')):

              b[-1] = hline[1:]

          if hline.startswith((' ', '-')):

              a[-1] = hline

          hunk[-1] = hline

      def testhunk(a, b, bstart):

          """Compare the lines in a with the lines in b

          a is assumed to have a control char at the start of each line, this char

          is ignored in the compare.

          """

          alen = len(a)

          blen = len(b)

          if alen > blen - bstart or bstart < 0:

              return False

          for i in pycompat.xrange(alen):

              if a[i][1:] != b[i + bstart]:

                  return False

          return True

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				# diffhelper.py - helper routines for patch
				#
				# 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

				from .i18n import _

				from . import (
				error,
				pycompat,
				)

				def addlines(fp, hunk, lena, lenb, a, b):
				"""Read lines from fp into the hunk

				The hunk is parsed into two arrays, a and b. a gets the old state of
				the text, b gets the new state. The control char from the hunk is saved
				when inserting into a, but not b (for performance while deleting files.)
				"""
				while True:
				todoa = lena - len(a)
				todob = lenb - len(b)
				num = max(todoa, todob)
				if num == 0:
				break
				for i in pycompat.xrange(num):
				s = fp.readline()
				if not s:
				raise error.ParseError(_('incomplete hunk'))
				if s == "\\ No newline at end of file\n":
				fixnewline(hunk, a, b)
				continue
				if s == '\n' or s == '\r\n':
				# Some patches may be missing the control char
				# on empty lines. Supply a leading space.
				s = ' ' + s
				hunk.append(s)
				if s.startswith('+'):
				b.append(s[1:])
				elif s.startswith('-'):
				a.append(s)
				else:
				b.append(s[1:])
				a.append(s)

				def fixnewline(hunk, a, b):
				"""Fix up the last lines of a and b when the patch has no newline at EOF"""
				l = hunk[-1]
				# tolerate CRLF in last line
				if l.endswith('\r\n'):
				hline = l[:-2]
				else:
				hline = l[:-1]

				if hline.startswith((' ', '+')):
				b[-1] = hline[1:]
				if hline.startswith((' ', '-')):
				a[-1] = hline
				hunk[-1] = hline

				def testhunk(a, b, bstart):
				"""Compare the lines in a with the lines in b

				a is assumed to have a control char at the start of each line, this char
				is ignored in the compare.
				"""
				alen = len(a)
				blen = len(b)
				if alen > blen - bstart or bstart < 0:
				return False
				for i in pycompat.xrange(alen):
				if a[i][1:] != b[i + bstart]:
				return False
				return True